[AssumeBundles] Dereferenceable used in bundle only applies at assume.

[fhahn]

Update LangRef and code using Dereferenceable in assume bundles to only use the information if it is safe at the point of use.

Dereferenceable in an assume bundle is only guaranteed at the point of the assumption, but may not be guaranteed at later points, because the pointer may have been freed.

Update code using Dereferenceable to only use it if the pointer cannot be freed. This can further be refined to check if the pointer could be freed between assume and use.

This follows up on #123196.

With that change, it should be safe to expose dereferenceable assumptions more widely as in
#121789

[llvmbot]

@llvm/pr-subscribers-llvm-transforms

@llvm/pr-subscribers-llvm-analysis

Author: Florian Hahn (fhahn)

Changes

Update LangRef and code using Dereferenceable in assume bundles to only use the information if it is safe at the point of use.

Dereferenceable in an assume bundle is only guaranteed at the point of the assumption, but may not be guaranteed at later points, because the pointer may have been freed.

Update code using Dereferenceable to only use it if the pointer cannot be freed. This can further be refined to check if the pointer could be freed between assume and use.

This follows up on #123196.

With that change, it should be safe to expose dereferenceable assumptions more widely as in
#121789

---

Full diff: https://github.com/llvm/llvm-project/pull/126117.diff

8 Files Affected:

• (modified) llvm/docs/LangRef.rst (+5-1)
• (modified) llvm/lib/Analysis/Loads.cpp (+1-3)
• (modified) llvm/lib/Analysis/ValueTracking.cpp (+1-1)
• (modified) llvm/test/Analysis/ValueTracking/assume-queries-counter.ll (+1-1)
• (modified) llvm/test/Analysis/ValueTracking/assume.ll (+2-2)
• (modified) llvm/test/Transforms/LICM/hoist-speculatable-load.ll (+55-1)
• (modified) llvm/test/Transforms/LoopVectorize/dereferenceable-info-from-assumption-constant-size.ll (+1-3)
• (modified) llvm/test/Transforms/SimplifyCFG/speculate-derefable-load.ll (+64-4)

diff --git a/llvm/docs/LangRef.rst b/llvm/docs/LangRef.rst index 8891aedcb58e552..f4d6affab8f9c3e 100644 --- a/llvm/docs/LangRef.rst +++ b/llvm/docs/LangRef.rst @@ -1474,7 +1474,11 @@ Currently, only the following parameter attributes are defined: ``null_pointer_is_valid`` function attribute is present. ``n`` should be a positive number. The pointer should be well defined, otherwise it is undefined behavior. This means ``dereferenceable(<n>)`` - implies ``noundef``. + implies ``noundef``. When ``dereferenceable(<n>)`` is used in an + :ref:`assume operand bundls <assume_opbundles>`, the pointer is only + guaranteed to be dereferenceable at the point of the assumption and + may not be dereferenceable at later pointers, e.g. because it could have + been freed. ``dereferenceable_or_null(<n>)`` This indicates that the parameter or return value isn't both diff --git a/llvm/lib/Analysis/Loads.cpp b/llvm/lib/Analysis/Loads.cpp index 733a7988e5a730a..91ae944d2e68366 100644 --- a/llvm/lib/Analysis/Loads.cpp +++ b/llvm/lib/Analysis/Loads.cpp @@ -26,8 +26,6 @@ using namespace llvm; -extern cl::opt<bool> UseDerefAtPointSemantics; - static bool isAligned(const Value *Base, Align Alignment, const DataLayout &DL) { return Base->getPointerAlignment(DL) >= Alignment; @@ -171,7 +169,7 @@ static bool isDereferenceableAndAlignedPointer( Size, DL, CtxI, AC, DT, TLI, Visited, MaxDepth); - if (CtxI && (!UseDerefAtPointSemantics || !V->canBeFreed())) { + if (CtxI && !V->canBeFreed()) { /// Look through assumes to see if both dereferencability and alignment can /// be proven by an assume if needed. RetainedKnowledge AlignRK; diff --git a/llvm/lib/Analysis/ValueTracking.cpp b/llvm/lib/Analysis/ValueTracking.cpp index 6eba6c0f08c3f40..eac11ca379932ba 100644 --- a/llvm/lib/Analysis/ValueTracking.cpp +++ b/llvm/lib/Analysis/ValueTracking.cpp @@ -626,7 +626,7 @@ static bool isKnownNonZeroFromAssume(const Value *V, const SimplifyQuery &Q) { *I, I->bundle_op_info_begin()[Elem.Index])) { if (RK.WasOn == V && (RK.AttrKind == Attribute::NonNull || - (RK.AttrKind == Attribute::Dereferenceable && + (RK.AttrKind == Attribute::Dereferenceable && !V->canBeFreed() && !NullPointerIsDefined(Q.CxtI->getFunction(), V->getType()->getPointerAddressSpace()))) && isValidAssumeForContext(I, Q.CxtI, Q.DT)) diff --git a/llvm/test/Analysis/ValueTracking/assume-queries-counter.ll b/llvm/test/Analysis/ValueTracking/assume-queries-counter.ll index a53b90b7b448ae8..0223ab8c4b677ab 100644 --- a/llvm/test/Analysis/ValueTracking/assume-queries-counter.ll +++ b/llvm/test/Analysis/ValueTracking/assume-queries-counter.ll @@ -47,7 +47,7 @@ define dso_local i1 @test2(ptr readonly %0) { ret i1 %2 } -define dso_local i32 @test4(ptr readonly %0, i1 %cond) { +define dso_local i32 @test4(ptr readonly %0, i1 %cond) nofree nosync { ; COUNTER1-LABEL: @test4( ; COUNTER1-NEXT: call void @llvm.assume(i1 true) [ "dereferenceable"(ptr [[TMP0:%.*]], i32 4) ] ; COUNTER1-NEXT: br i1 [[COND:%.*]], label [[A:%.*]], label [[B:%.*]] diff --git a/llvm/test/Analysis/ValueTracking/assume.ll b/llvm/test/Analysis/ValueTracking/assume.ll index 4c4b46c41996868..298facfa3aa9d05 100644 --- a/llvm/test/Analysis/ValueTracking/assume.ll +++ b/llvm/test/Analysis/ValueTracking/assume.ll @@ -57,7 +57,7 @@ define dso_local i1 @test2(ptr readonly %0) { ret i1 %2 } -define dso_local i32 @test4(ptr readonly %0, i1 %cond) { +define dso_local i32 @test4(ptr readonly %0, i1 %cond) nofree nosync { ; CHECK-LABEL: @test4( ; CHECK-NEXT: call void @llvm.assume(i1 true) [ "dereferenceable"(ptr [[TMP0:%.*]], i32 4) ] ; CHECK-NEXT: br i1 [[COND:%.*]], label [[A:%.*]], label [[B:%.*]] @@ -91,7 +91,7 @@ A: ret i32 %6 } -define dso_local i32 @test4a(ptr readonly %0, i1 %cond) { +define dso_local i32 @test4a(ptr readonly %0, i1 %cond) nofree nosync { ; CHECK-LABEL: @test4a( ; CHECK-NEXT: call void @llvm.assume(i1 true) [ "dereferenceable"(ptr [[TMP0:%.*]], i32 4), "align"(ptr [[TMP0]], i32 8) ] ; CHECK-NEXT: br i1 [[COND:%.*]], label [[A:%.*]], label [[B:%.*]] diff --git a/llvm/test/Transforms/LICM/hoist-speculatable-load.ll b/llvm/test/Transforms/LICM/hoist-speculatable-load.ll index 752cf3e99cbf5a6..cf43ff9913813e3 100644 --- a/llvm/test/Transforms/LICM/hoist-speculatable-load.ll +++ b/llvm/test/Transforms/LICM/hoist-speculatable-load.ll @@ -11,12 +11,12 @@ define void @f(i32 %ptr_i, ptr %ptr2, i1 %cond) { ; CHECK-NEXT: store i32 0, ptr [[PTR2:%.*]], align 4 ; CHECK-NEXT: br label [[FOR_BODY_LR_PH]] ; CHECK: for.body.lr.ph: -; CHECK-NEXT: [[TMP0:%.*]] = load i32, ptr [[PTR]], align 4 ; CHECK-NEXT: br label [[FOR_BODY:%.*]] ; CHECK: for.body: ; CHECK-NEXT: [[I_08:%.*]] = phi i32 [ 0, [[FOR_BODY_LR_PH]] ], [ [[INC:%.*]], [[IF_END:%.*]] ] ; CHECK-NEXT: br i1 [[COND]], label [[IF_END]], label [[IF:%.*]] ; CHECK: if: +; CHECK-NEXT: [[TMP0:%.*]] = load i32, ptr [[PTR]], align 4, !invariant.load [[META0:![0-9]+]] ; CHECK-NEXT: store i32 [[TMP0]], ptr [[PTR2]], align 4 ; CHECK-NEXT: br label [[IF_END]] ; CHECK: if.end: @@ -56,4 +56,58 @@ exit: ; preds = %if.end, %entry ret void } +define void @f_nofree_nosync(i32 %ptr_i, ptr %ptr2, i1 %cond) nofree nosync { +; CHECK-LABEL: @f_nofree_nosync( +; CHECK-NEXT: entry: +; CHECK-NEXT: [[PTR:%.*]] = inttoptr i32 [[PTR_I:%.*]] to ptr +; CHECK-NEXT: call void @llvm.assume(i1 true) [ "align"(ptr [[PTR]], i32 16), "dereferenceable"(ptr [[PTR]], i32 16) ] +; CHECK-NEXT: br i1 [[COND:%.*]], label [[FOR_BODY_LR_PH:%.*]], label [[IF0:%.*]] +; CHECK: if0: +; CHECK-NEXT: store i32 0, ptr [[PTR2:%.*]], align 4 +; CHECK-NEXT: br label [[FOR_BODY_LR_PH]] +; CHECK: for.body.lr.ph: +; CHECK-NEXT: br label [[FOR_BODY:%.*]] +; CHECK: for.body: +; CHECK-NEXT: [[I_08:%.*]] = phi i32 [ 0, [[FOR_BODY_LR_PH]] ], [ [[INC:%.*]], [[IF_END:%.*]] ] +; CHECK-NEXT: br i1 [[COND]], label [[IF_END]], label [[IF:%.*]] +; CHECK: if: +; CHECK-NEXT: [[TMP0:%.*]] = load i32, ptr [[PTR]], align 4, !invariant.load [[META0]] +; CHECK-NEXT: store i32 [[TMP0]], ptr [[PTR2]], align 4 +; CHECK-NEXT: br label [[IF_END]] +; CHECK: if.end: +; CHECK-NEXT: [[INC]] = add nuw nsw i32 [[I_08]], 1 +; CHECK-NEXT: [[CMP:%.*]] = icmp slt i32 [[INC]], 2 +; CHECK-NEXT: br i1 [[CMP]], label [[FOR_BODY]], label [[EXIT:%.*]] +; CHECK: exit: +; CHECK-NEXT: ret void +; +entry: + %ptr = inttoptr i32 %ptr_i to ptr + call void @llvm.assume(i1 true) [ "align"(ptr %ptr, i32 16), "dereferenceable"(ptr %ptr, i32 16) ] + br i1 %cond, label %for.body.lr.ph, label %if0 + +if0: + store i32 0, ptr %ptr2, align 4 + br label %for.body.lr.ph + +for.body.lr.ph: ; preds = %entry + br label %for.body + +for.body: ; preds = %for.body.lr.ph, %if.end + %i.08 = phi i32 [ 0, %for.body.lr.ph ], [ %inc, %if.end ] + br i1 %cond, label %if.end, label %if + +if: + %0 = load i32, ptr %ptr, align 4, !invariant.load !{} + store i32 %0, ptr %ptr2, align 4 + br label %if.end + +if.end: ; preds = %for.body + %inc = add nuw nsw i32 %i.08, 1 + %cmp = icmp slt i32 %inc, 2 + br i1 %cmp, label %for.body, label %exit + +exit: ; preds = %if.end, %entry + ret void +} declare void @llvm.assume(i1 noundef) diff --git a/llvm/test/Transforms/LoopVectorize/dereferenceable-info-from-assumption-constant-size.ll b/llvm/test/Transforms/LoopVectorize/dereferenceable-info-from-assumption-constant-size.ll index 90671689f1dce05..13780a684f9ce79 100644 --- a/llvm/test/Transforms/LoopVectorize/dereferenceable-info-from-assumption-constant-size.ll +++ b/llvm/test/Transforms/LoopVectorize/dereferenceable-info-from-assumption-constant-size.ll @@ -1,5 +1,5 @@ ; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --version 5 -; RUN: opt -p loop-vectorize -force-vector-width=2 -use-dereferenceable-at-point-semantics -S %s | FileCheck %s +; RUN: opt -p loop-vectorize -force-vector-width=2 -S %s | FileCheck %s declare void @llvm.assume(i1) @@ -1411,7 +1411,6 @@ exit: } ; %a may be freed between the dereferenceable assumption and accesses. -; It is not safe to use with -use-dereferenceable-at-point-semantics. define void @may_free_align_deref_assumption_in_header_constant_trip_count_loop_invariant_ptr(ptr noalias %a, ptr noalias %b, ptr noalias %c) { ; CHECK-LABEL: define void @may_free_align_deref_assumption_in_header_constant_trip_count_loop_invariant_ptr( ; CHECK-SAME: ptr noalias [[A:%.*]], ptr noalias [[B:%.*]], ptr noalias [[C:%.*]]) { @@ -1505,7 +1504,6 @@ exit: } ; %a may be freed between the dereferenceable assumption and accesses. -; It is not safe to use with -use-dereferenceable-at-point-semantics. define void @may_free_local_ptr_align_deref_assumption_in_header_constant_trip_count_loop_invariant_ptr(ptr noalias %b, ptr noalias %c) nofree nosync { ; CHECK-LABEL: define void @may_free_local_ptr_align_deref_assumption_in_header_constant_trip_count_loop_invariant_ptr( ; CHECK-SAME: ptr noalias [[B:%.*]], ptr noalias [[C:%.*]]) #[[ATTR1]] { diff --git a/llvm/test/Transforms/SimplifyCFG/speculate-derefable-load.ll b/llvm/test/Transforms/SimplifyCFG/speculate-derefable-load.ll index 0138433312ed84a..b8c999d700aa7da 100644 --- a/llvm/test/Transforms/SimplifyCFG/speculate-derefable-load.ll +++ b/llvm/test/Transforms/SimplifyCFG/speculate-derefable-load.ll @@ -4,10 +4,14 @@ define i64 @align_deref_align(i1 %c, ptr %p) { ; CHECK-LABEL: define i64 @align_deref_align( ; CHECK-SAME: i1 [[C:%.*]], ptr [[P:%.*]]) { -; CHECK-NEXT: [[ENTRY:.*:]] +; CHECK-NEXT: [[ENTRY:.*]]: ; CHECK-NEXT: call void @llvm.assume(i1 true) [ "dereferenceable"(ptr [[P]], i64 8), "align"(ptr [[P]], i64 8) ] +; CHECK-NEXT: br i1 [[C]], label %[[IF:.*]], label %[[EXIT:.*]] +; CHECK: [[IF]]: ; CHECK-NEXT: [[V:%.*]] = load i64, ptr [[P]], align 8 -; CHECK-NEXT: [[RES:%.*]] = select i1 [[C]], i64 [[V]], i64 0 +; CHECK-NEXT: br label %[[EXIT]] +; CHECK: [[EXIT]]: +; CHECK-NEXT: [[RES:%.*]] = phi i64 [ [[V]], %[[IF]] ], [ 0, %[[ENTRY]] ] ; CHECK-NEXT: ret i64 [[RES]] ; entry: @@ -23,9 +27,64 @@ exit: ret i64 %res } +define i64 @align_deref_align_nofree_nosync(i1 %c, ptr %p) nofree nosync { +; CHECK-LABEL: define i64 @align_deref_align_nofree_nosync( +; CHECK-SAME: i1 [[C:%.*]], ptr [[P:%.*]]) #[[ATTR0:[0-9]+]] { +; CHECK-NEXT: [[ENTRY:.*:]] +; CHECK-NEXT: call void @llvm.assume(i1 true) [ "dereferenceable"(ptr [[P]], i64 8), "align"(ptr [[P]], i64 8) ] +; CHECK-NEXT: [[V:%.*]] = load i64, ptr [[P]], align 8 +; CHECK-NEXT: [[SPEC_SELECT:%.*]] = select i1 [[C]], i64 [[V]], i64 0 +; CHECK-NEXT: ret i64 [[SPEC_SELECT]] +; +entry: + call void @llvm.assume(i1 true) [ "dereferenceable"(ptr %p, i64 8), "align"(ptr %p, i64 8) ] + br i1 %c, label %if, label %exit + +if: + %v = load i64, ptr %p, align 8 + br label %exit + +exit: + %res = phi i64 [ %v, %if ], [ 0, %entry ] + ret i64 %res +} + define i64 @assume_deref_align2(i1 %c1, i32 %x, ptr %p) { ; CHECK-LABEL: define i64 @assume_deref_align2( ; CHECK-SAME: i1 [[C1:%.*]], i32 [[X:%.*]], ptr [[P:%.*]]) { +; CHECK-NEXT: [[ENTRY:.*]]: +; CHECK-NEXT: call void @llvm.assume(i1 true) [ "dereferenceable"(ptr [[P]], i64 8), "align"(ptr [[P]], i64 8) ] +; CHECK-NEXT: br i1 [[C1]], label %[[IF1:.*]], label %[[EXIT:.*]] +; CHECK: [[IF1]]: +; CHECK-NEXT: [[C2:%.*]] = icmp ugt i32 [[X]], 10 +; CHECK-NEXT: br i1 [[C2]], label %[[IF2:.*]], label %[[EXIT]] +; CHECK: [[IF2]]: +; CHECK-NEXT: [[V:%.*]] = load i64, ptr [[P]], align 8 +; CHECK-NEXT: br label %[[EXIT]] +; CHECK: [[EXIT]]: +; CHECK-NEXT: [[RES:%.*]] = phi i64 [ [[V]], %[[IF2]] ], [ 1, %[[IF1]] ], [ 0, %[[ENTRY]] ] +; CHECK-NEXT: ret i64 [[RES]] +; +entry: + call void @llvm.assume(i1 true) [ "dereferenceable"(ptr %p, i64 8), "align"(ptr %p, i64 8) ] + br i1 %c1, label %if1, label %exit + +if1: + %c2 = icmp ugt i32 %x, 10 + br i1 %c2, label %if2, label %exit + +if2: + %v = load i64, ptr %p, align 8 + br label %exit + +exit: + %res = phi i64 [ %v, %if2 ], [ 1, %if1 ], [ 0, %entry ] + ret i64 %res +} + +define i64 @assume_deref_align2_nofree_nosync(i1 %c1, i32 %x, ptr %p) nofree nosync { +; CHECK-LABEL: define i64 @assume_deref_align2_nofree_nosync( +; CHECK-SAME: i1 [[C1:%.*]], i32 [[X:%.*]], ptr [[P:%.*]]) #[[ATTR0]] { ; CHECK-NEXT: [[ENTRY:.*:]] ; CHECK-NEXT: call void @llvm.assume(i1 true) [ "dereferenceable"(ptr [[P]], i64 8), "align"(ptr [[P]], i64 8) ] ; CHECK-NEXT: [[C2:%.*]] = icmp ugt i32 [[X]], 10 @@ -51,9 +110,10 @@ exit: ret i64 %res } -define i64 @assume_deref_align_not_dominating(i1 %c, ptr %p) { + +define i64 @assume_deref_align_not_dominating(i1 %c, ptr %p) nofree nosync { ; CHECK-LABEL: define i64 @assume_deref_align_not_dominating( -; CHECK-SAME: i1 [[C:%.*]], ptr [[P:%.*]]) { +; CHECK-SAME: i1 [[C:%.*]], ptr [[P:%.*]]) #[[ATTR0]] { ; CHECK-NEXT: [[ENTRY:.*]]: ; CHECK-NEXT: br i1 [[C]], label %[[IF:.*]], label %[[EXIT:.*]] ; CHECK: [[IF]]: 

[llvmbot]

@llvm/pr-subscribers-llvm-ir

Author: Florian Hahn (fhahn)

Changes

Update LangRef and code using Dereferenceable in assume bundles to only use the information if it is safe at the point of use.

Dereferenceable in an assume bundle is only guaranteed at the point of the assumption, but may not be guaranteed at later points, because the pointer may have been freed.

Update code using Dereferenceable to only use it if the pointer cannot be freed. This can further be refined to check if the pointer could be freed between assume and use.

This follows up on #123196.

With that change, it should be safe to expose dereferenceable assumptions more widely as in
#121789

---

Full diff: https://github.com/llvm/llvm-project/pull/126117.diff

8 Files Affected:

• (modified) llvm/docs/LangRef.rst (+5-1)
• (modified) llvm/lib/Analysis/Loads.cpp (+1-3)
• (modified) llvm/lib/Analysis/ValueTracking.cpp (+1-1)
• (modified) llvm/test/Analysis/ValueTracking/assume-queries-counter.ll (+1-1)
• (modified) llvm/test/Analysis/ValueTracking/assume.ll (+2-2)
• (modified) llvm/test/Transforms/LICM/hoist-speculatable-load.ll (+55-1)
• (modified) llvm/test/Transforms/LoopVectorize/dereferenceable-info-from-assumption-constant-size.ll (+1-3)
• (modified) llvm/test/Transforms/SimplifyCFG/speculate-derefable-load.ll (+64-4)

diff --git a/llvm/docs/LangRef.rst b/llvm/docs/LangRef.rst index 8891aedcb58e552..f4d6affab8f9c3e 100644 --- a/llvm/docs/LangRef.rst +++ b/llvm/docs/LangRef.rst @@ -1474,7 +1474,11 @@ Currently, only the following parameter attributes are defined: ``null_pointer_is_valid`` function attribute is present. ``n`` should be a positive number. The pointer should be well defined, otherwise it is undefined behavior. This means ``dereferenceable(<n>)`` - implies ``noundef``. + implies ``noundef``. When ``dereferenceable(<n>)`` is used in an + :ref:`assume operand bundls <assume_opbundles>`, the pointer is only + guaranteed to be dereferenceable at the point of the assumption and + may not be dereferenceable at later pointers, e.g. because it could have + been freed. ``dereferenceable_or_null(<n>)`` This indicates that the parameter or return value isn't both diff --git a/llvm/lib/Analysis/Loads.cpp b/llvm/lib/Analysis/Loads.cpp index 733a7988e5a730a..91ae944d2e68366 100644 --- a/llvm/lib/Analysis/Loads.cpp +++ b/llvm/lib/Analysis/Loads.cpp @@ -26,8 +26,6 @@ using namespace llvm; -extern cl::opt<bool> UseDerefAtPointSemantics; - static bool isAligned(const Value *Base, Align Alignment, const DataLayout &DL) { return Base->getPointerAlignment(DL) >= Alignment; @@ -171,7 +169,7 @@ static bool isDereferenceableAndAlignedPointer( Size, DL, CtxI, AC, DT, TLI, Visited, MaxDepth); - if (CtxI && (!UseDerefAtPointSemantics || !V->canBeFreed())) { + if (CtxI && !V->canBeFreed()) { /// Look through assumes to see if both dereferencability and alignment can /// be proven by an assume if needed. RetainedKnowledge AlignRK; diff --git a/llvm/lib/Analysis/ValueTracking.cpp b/llvm/lib/Analysis/ValueTracking.cpp index 6eba6c0f08c3f40..eac11ca379932ba 100644 --- a/llvm/lib/Analysis/ValueTracking.cpp +++ b/llvm/lib/Analysis/ValueTracking.cpp @@ -626,7 +626,7 @@ static bool isKnownNonZeroFromAssume(const Value *V, const SimplifyQuery &Q) { *I, I->bundle_op_info_begin()[Elem.Index])) { if (RK.WasOn == V && (RK.AttrKind == Attribute::NonNull || - (RK.AttrKind == Attribute::Dereferenceable && + (RK.AttrKind == Attribute::Dereferenceable && !V->canBeFreed() && !NullPointerIsDefined(Q.CxtI->getFunction(), V->getType()->getPointerAddressSpace()))) && isValidAssumeForContext(I, Q.CxtI, Q.DT)) diff --git a/llvm/test/Analysis/ValueTracking/assume-queries-counter.ll b/llvm/test/Analysis/ValueTracking/assume-queries-counter.ll index a53b90b7b448ae8..0223ab8c4b677ab 100644 --- a/llvm/test/Analysis/ValueTracking/assume-queries-counter.ll +++ b/llvm/test/Analysis/ValueTracking/assume-queries-counter.ll @@ -47,7 +47,7 @@ define dso_local i1 @test2(ptr readonly %0) { ret i1 %2 } -define dso_local i32 @test4(ptr readonly %0, i1 %cond) { +define dso_local i32 @test4(ptr readonly %0, i1 %cond) nofree nosync { ; COUNTER1-LABEL: @test4( ; COUNTER1-NEXT: call void @llvm.assume(i1 true) [ "dereferenceable"(ptr [[TMP0:%.*]], i32 4) ] ; COUNTER1-NEXT: br i1 [[COND:%.*]], label [[A:%.*]], label [[B:%.*]] diff --git a/llvm/test/Analysis/ValueTracking/assume.ll b/llvm/test/Analysis/ValueTracking/assume.ll index 4c4b46c41996868..298facfa3aa9d05 100644 --- a/llvm/test/Analysis/ValueTracking/assume.ll +++ b/llvm/test/Analysis/ValueTracking/assume.ll @@ -57,7 +57,7 @@ define dso_local i1 @test2(ptr readonly %0) { ret i1 %2 } -define dso_local i32 @test4(ptr readonly %0, i1 %cond) { +define dso_local i32 @test4(ptr readonly %0, i1 %cond) nofree nosync { ; CHECK-LABEL: @test4( ; CHECK-NEXT: call void @llvm.assume(i1 true) [ "dereferenceable"(ptr [[TMP0:%.*]], i32 4) ] ; CHECK-NEXT: br i1 [[COND:%.*]], label [[A:%.*]], label [[B:%.*]] @@ -91,7 +91,7 @@ A: ret i32 %6 } -define dso_local i32 @test4a(ptr readonly %0, i1 %cond) { +define dso_local i32 @test4a(ptr readonly %0, i1 %cond) nofree nosync { ; CHECK-LABEL: @test4a( ; CHECK-NEXT: call void @llvm.assume(i1 true) [ "dereferenceable"(ptr [[TMP0:%.*]], i32 4), "align"(ptr [[TMP0]], i32 8) ] ; CHECK-NEXT: br i1 [[COND:%.*]], label [[A:%.*]], label [[B:%.*]] diff --git a/llvm/test/Transforms/LICM/hoist-speculatable-load.ll b/llvm/test/Transforms/LICM/hoist-speculatable-load.ll index 752cf3e99cbf5a6..cf43ff9913813e3 100644 --- a/llvm/test/Transforms/LICM/hoist-speculatable-load.ll +++ b/llvm/test/Transforms/LICM/hoist-speculatable-load.ll @@ -11,12 +11,12 @@ define void @f(i32 %ptr_i, ptr %ptr2, i1 %cond) { ; CHECK-NEXT: store i32 0, ptr [[PTR2:%.*]], align 4 ; CHECK-NEXT: br label [[FOR_BODY_LR_PH]] ; CHECK: for.body.lr.ph: -; CHECK-NEXT: [[TMP0:%.*]] = load i32, ptr [[PTR]], align 4 ; CHECK-NEXT: br label [[FOR_BODY:%.*]] ; CHECK: for.body: ; CHECK-NEXT: [[I_08:%.*]] = phi i32 [ 0, [[FOR_BODY_LR_PH]] ], [ [[INC:%.*]], [[IF_END:%.*]] ] ; CHECK-NEXT: br i1 [[COND]], label [[IF_END]], label [[IF:%.*]] ; CHECK: if: +; CHECK-NEXT: [[TMP0:%.*]] = load i32, ptr [[PTR]], align 4, !invariant.load [[META0:![0-9]+]] ; CHECK-NEXT: store i32 [[TMP0]], ptr [[PTR2]], align 4 ; CHECK-NEXT: br label [[IF_END]] ; CHECK: if.end: @@ -56,4 +56,58 @@ exit: ; preds = %if.end, %entry ret void } +define void @f_nofree_nosync(i32 %ptr_i, ptr %ptr2, i1 %cond) nofree nosync { +; CHECK-LABEL: @f_nofree_nosync( +; CHECK-NEXT: entry: +; CHECK-NEXT: [[PTR:%.*]] = inttoptr i32 [[PTR_I:%.*]] to ptr +; CHECK-NEXT: call void @llvm.assume(i1 true) [ "align"(ptr [[PTR]], i32 16), "dereferenceable"(ptr [[PTR]], i32 16) ] +; CHECK-NEXT: br i1 [[COND:%.*]], label [[FOR_BODY_LR_PH:%.*]], label [[IF0:%.*]] +; CHECK: if0: +; CHECK-NEXT: store i32 0, ptr [[PTR2:%.*]], align 4 +; CHECK-NEXT: br label [[FOR_BODY_LR_PH]] +; CHECK: for.body.lr.ph: +; CHECK-NEXT: br label [[FOR_BODY:%.*]] +; CHECK: for.body: +; CHECK-NEXT: [[I_08:%.*]] = phi i32 [ 0, [[FOR_BODY_LR_PH]] ], [ [[INC:%.*]], [[IF_END:%.*]] ] +; CHECK-NEXT: br i1 [[COND]], label [[IF_END]], label [[IF:%.*]] +; CHECK: if: +; CHECK-NEXT: [[TMP0:%.*]] = load i32, ptr [[PTR]], align 4, !invariant.load [[META0]] +; CHECK-NEXT: store i32 [[TMP0]], ptr [[PTR2]], align 4 +; CHECK-NEXT: br label [[IF_END]] +; CHECK: if.end: +; CHECK-NEXT: [[INC]] = add nuw nsw i32 [[I_08]], 1 +; CHECK-NEXT: [[CMP:%.*]] = icmp slt i32 [[INC]], 2 +; CHECK-NEXT: br i1 [[CMP]], label [[FOR_BODY]], label [[EXIT:%.*]] +; CHECK: exit: +; CHECK-NEXT: ret void +; +entry: + %ptr = inttoptr i32 %ptr_i to ptr + call void @llvm.assume(i1 true) [ "align"(ptr %ptr, i32 16), "dereferenceable"(ptr %ptr, i32 16) ] + br i1 %cond, label %for.body.lr.ph, label %if0 + +if0: + store i32 0, ptr %ptr2, align 4 + br label %for.body.lr.ph + +for.body.lr.ph: ; preds = %entry + br label %for.body + +for.body: ; preds = %for.body.lr.ph, %if.end + %i.08 = phi i32 [ 0, %for.body.lr.ph ], [ %inc, %if.end ] + br i1 %cond, label %if.end, label %if + +if: + %0 = load i32, ptr %ptr, align 4, !invariant.load !{} + store i32 %0, ptr %ptr2, align 4 + br label %if.end + +if.end: ; preds = %for.body + %inc = add nuw nsw i32 %i.08, 1 + %cmp = icmp slt i32 %inc, 2 + br i1 %cmp, label %for.body, label %exit + +exit: ; preds = %if.end, %entry + ret void +} declare void @llvm.assume(i1 noundef) diff --git a/llvm/test/Transforms/LoopVectorize/dereferenceable-info-from-assumption-constant-size.ll b/llvm/test/Transforms/LoopVectorize/dereferenceable-info-from-assumption-constant-size.ll index 90671689f1dce05..13780a684f9ce79 100644 --- a/llvm/test/Transforms/LoopVectorize/dereferenceable-info-from-assumption-constant-size.ll +++ b/llvm/test/Transforms/LoopVectorize/dereferenceable-info-from-assumption-constant-size.ll @@ -1,5 +1,5 @@ ; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --version 5 -; RUN: opt -p loop-vectorize -force-vector-width=2 -use-dereferenceable-at-point-semantics -S %s | FileCheck %s +; RUN: opt -p loop-vectorize -force-vector-width=2 -S %s | FileCheck %s declare void @llvm.assume(i1) @@ -1411,7 +1411,6 @@ exit: } ; %a may be freed between the dereferenceable assumption and accesses. -; It is not safe to use with -use-dereferenceable-at-point-semantics. define void @may_free_align_deref_assumption_in_header_constant_trip_count_loop_invariant_ptr(ptr noalias %a, ptr noalias %b, ptr noalias %c) { ; CHECK-LABEL: define void @may_free_align_deref_assumption_in_header_constant_trip_count_loop_invariant_ptr( ; CHECK-SAME: ptr noalias [[A:%.*]], ptr noalias [[B:%.*]], ptr noalias [[C:%.*]]) { @@ -1505,7 +1504,6 @@ exit: } ; %a may be freed between the dereferenceable assumption and accesses. -; It is not safe to use with -use-dereferenceable-at-point-semantics. define void @may_free_local_ptr_align_deref_assumption_in_header_constant_trip_count_loop_invariant_ptr(ptr noalias %b, ptr noalias %c) nofree nosync { ; CHECK-LABEL: define void @may_free_local_ptr_align_deref_assumption_in_header_constant_trip_count_loop_invariant_ptr( ; CHECK-SAME: ptr noalias [[B:%.*]], ptr noalias [[C:%.*]]) #[[ATTR1]] { diff --git a/llvm/test/Transforms/SimplifyCFG/speculate-derefable-load.ll b/llvm/test/Transforms/SimplifyCFG/speculate-derefable-load.ll index 0138433312ed84a..b8c999d700aa7da 100644 --- a/llvm/test/Transforms/SimplifyCFG/speculate-derefable-load.ll +++ b/llvm/test/Transforms/SimplifyCFG/speculate-derefable-load.ll @@ -4,10 +4,14 @@ define i64 @align_deref_align(i1 %c, ptr %p) { ; CHECK-LABEL: define i64 @align_deref_align( ; CHECK-SAME: i1 [[C:%.*]], ptr [[P:%.*]]) { -; CHECK-NEXT: [[ENTRY:.*:]] +; CHECK-NEXT: [[ENTRY:.*]]: ; CHECK-NEXT: call void @llvm.assume(i1 true) [ "dereferenceable"(ptr [[P]], i64 8), "align"(ptr [[P]], i64 8) ] +; CHECK-NEXT: br i1 [[C]], label %[[IF:.*]], label %[[EXIT:.*]] +; CHECK: [[IF]]: ; CHECK-NEXT: [[V:%.*]] = load i64, ptr [[P]], align 8 -; CHECK-NEXT: [[RES:%.*]] = select i1 [[C]], i64 [[V]], i64 0 +; CHECK-NEXT: br label %[[EXIT]] +; CHECK: [[EXIT]]: +; CHECK-NEXT: [[RES:%.*]] = phi i64 [ [[V]], %[[IF]] ], [ 0, %[[ENTRY]] ] ; CHECK-NEXT: ret i64 [[RES]] ; entry: @@ -23,9 +27,64 @@ exit: ret i64 %res } +define i64 @align_deref_align_nofree_nosync(i1 %c, ptr %p) nofree nosync { +; CHECK-LABEL: define i64 @align_deref_align_nofree_nosync( +; CHECK-SAME: i1 [[C:%.*]], ptr [[P:%.*]]) #[[ATTR0:[0-9]+]] { +; CHECK-NEXT: [[ENTRY:.*:]] +; CHECK-NEXT: call void @llvm.assume(i1 true) [ "dereferenceable"(ptr [[P]], i64 8), "align"(ptr [[P]], i64 8) ] +; CHECK-NEXT: [[V:%.*]] = load i64, ptr [[P]], align 8 +; CHECK-NEXT: [[SPEC_SELECT:%.*]] = select i1 [[C]], i64 [[V]], i64 0 +; CHECK-NEXT: ret i64 [[SPEC_SELECT]] +; +entry: + call void @llvm.assume(i1 true) [ "dereferenceable"(ptr %p, i64 8), "align"(ptr %p, i64 8) ] + br i1 %c, label %if, label %exit + +if: + %v = load i64, ptr %p, align 8 + br label %exit + +exit: + %res = phi i64 [ %v, %if ], [ 0, %entry ] + ret i64 %res +} + define i64 @assume_deref_align2(i1 %c1, i32 %x, ptr %p) { ; CHECK-LABEL: define i64 @assume_deref_align2( ; CHECK-SAME: i1 [[C1:%.*]], i32 [[X:%.*]], ptr [[P:%.*]]) { +; CHECK-NEXT: [[ENTRY:.*]]: +; CHECK-NEXT: call void @llvm.assume(i1 true) [ "dereferenceable"(ptr [[P]], i64 8), "align"(ptr [[P]], i64 8) ] +; CHECK-NEXT: br i1 [[C1]], label %[[IF1:.*]], label %[[EXIT:.*]] +; CHECK: [[IF1]]: +; CHECK-NEXT: [[C2:%.*]] = icmp ugt i32 [[X]], 10 +; CHECK-NEXT: br i1 [[C2]], label %[[IF2:.*]], label %[[EXIT]] +; CHECK: [[IF2]]: +; CHECK-NEXT: [[V:%.*]] = load i64, ptr [[P]], align 8 +; CHECK-NEXT: br label %[[EXIT]] +; CHECK: [[EXIT]]: +; CHECK-NEXT: [[RES:%.*]] = phi i64 [ [[V]], %[[IF2]] ], [ 1, %[[IF1]] ], [ 0, %[[ENTRY]] ] +; CHECK-NEXT: ret i64 [[RES]] +; +entry: + call void @llvm.assume(i1 true) [ "dereferenceable"(ptr %p, i64 8), "align"(ptr %p, i64 8) ] + br i1 %c1, label %if1, label %exit + +if1: + %c2 = icmp ugt i32 %x, 10 + br i1 %c2, label %if2, label %exit + +if2: + %v = load i64, ptr %p, align 8 + br label %exit + +exit: + %res = phi i64 [ %v, %if2 ], [ 1, %if1 ], [ 0, %entry ] + ret i64 %res +} + +define i64 @assume_deref_align2_nofree_nosync(i1 %c1, i32 %x, ptr %p) nofree nosync { +; CHECK-LABEL: define i64 @assume_deref_align2_nofree_nosync( +; CHECK-SAME: i1 [[C1:%.*]], i32 [[X:%.*]], ptr [[P:%.*]]) #[[ATTR0]] { ; CHECK-NEXT: [[ENTRY:.*:]] ; CHECK-NEXT: call void @llvm.assume(i1 true) [ "dereferenceable"(ptr [[P]], i64 8), "align"(ptr [[P]], i64 8) ] ; CHECK-NEXT: [[C2:%.*]] = icmp ugt i32 [[X]], 10 @@ -51,9 +110,10 @@ exit: ret i64 %res } -define i64 @assume_deref_align_not_dominating(i1 %c, ptr %p) { + +define i64 @assume_deref_align_not_dominating(i1 %c, ptr %p) nofree nosync { ; CHECK-LABEL: define i64 @assume_deref_align_not_dominating( -; CHECK-SAME: i1 [[C:%.*]], ptr [[P:%.*]]) { +; CHECK-SAME: i1 [[C:%.*]], ptr [[P:%.*]]) #[[ATTR0]] { ; CHECK-NEXT: [[ENTRY:.*]]: ; CHECK-NEXT: br i1 [[C]], label %[[IF:.*]], label %[[EXIT:.*]] ; CHECK: [[IF]]: 

[nikic]

I don't think you need this change. Even if the pointer is freed later, the fact that it was dereferenceable at some point implies that it is not null.

[fhahn]

Yep, removed again, thanks

[preames]

How effective are we at proving nofree and nosync these days? Do we need to consider some heuristic for a local "canBeFreedBetween(Assume,CtxI)"?

[preames]

I think you'd preserve test intent by adding nofree nosyc to this one (maybe with a name change), and then adding a separate one without it.

It isn't clear to my why with the additional attributes we still can't hoist the load. That's concerning?

[fhahn]

I added f_nofree_nosync below; the problem seems to be that %ptr is formed using inttoptr and Value::canBeFreed only applies to function arguments I think (it would be valid for the function to allocate and free locally).

So eventually we will probably need more powerful analysis.

[preames]

Maybe add a variant which doesn't involve the inttoptr then?

[fhahn]

Added a variant at the bottom, thanks

[preames]

"and may not be" seems like you're referring to the assumption at first. Maybe: ". The pointer may not be " (the rest of the sentence is fine)

[fhahn]

Updated, thanks!

[preames]

Maybe add a variant which doesn't involve the inttoptr then?

[fhahn]

How effective are we at proving nofree and nosync these days? Do we need to consider some heuristic for a local "canBeFreedBetween(Assume,CtxI)"?

I think nofree/nosync inference is reasonably effective, but the attributes can only be used with arguments; a function still could allocate/free memory used internally. I am planning to add such a heuristic as follow-up; as long as the assumption is in the preheader, we would need to there and the blocks in the loop.

[nikic]

LGTM

[nikic]

This is indented too far and ends up rendering weirdly.

[fhahn]

Should hopefully be fixed by 2d6330f

[jayfoad]

@fhahn am I right in thinking that this load could be hoisted, because the risk of %ptr being freed is only a concern if you want to move the load to a later point in the program, not an earlier point?

[ruiling]

The canBeFreed() stops moving the pointer use past free point in both directions currently. See the example at #120962 (comment). The free could appear before the pointer use inside if. Hoisting the pointer use for the case may change program behavior.