[InstCombine] Preserve profile after folding select instructions with conditionals #159666
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… conditionals If select simplification produces the transform: ``` (select A && B, T, F) -> (select A, T, F) ``` or ``` (select A || B, T, F) -> (select A, T, F) ``` it stands to reason that if the branches are the same, then the branch weights remain the same since the net effect is a simplification of the conditional. There are also cases where InstCombine negates the conditional (and therefore reverses the branches); this PR asserts that the branch weights are reversed in this case. Tracking issue: llvm#147390
llvmbot added llvm:instcombine 
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| @llvm/pr-subscribers-llvm-transforms Author: Alan Zhao (alanzhao1) ChangesIf or it stands to reason that if the branches are the same, then the branch weights remain the same since the net effect is a simplification of the conditional. There are also cases where InstCombine negates the conditional (and therefore reverses the branches); this PR asserts that the branch weights are reversed in this case. Tracking issue: #147390 Full diff: https://github.com/llvm/llvm-project/pull/159666.diff 4 Files Affected:
diff --git a/llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp b/llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp index 4ea75409252bd..b0513662628d5 100644 --- a/llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp +++ b/llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp @@ -4521,8 +4521,20 @@ Instruction *InstCombinerImpl::visitSelectInst(SelectInst &SI) { auto FoldSelectWithAndOrCond = [&](bool IsAnd, Value *A, Value *B) -> Instruction * { if (Value *V = simplifySelectInst(B, TrueVal, FalseVal, - SQ.getWithInstruction(&SI))) - return SelectInst::Create(A, IsAnd ? V : TrueVal, IsAnd ? FalseVal : V); + SQ.getWithInstruction(&SI))) { + Value *NewTrueVal = IsAnd ? V : TrueVal; + Value *NewFalseVal = IsAnd ? FalseVal : V; + + // If the True and False values don't change, then preserve the branch + // metadata of the original select as the net effect of this change is to + // simplify the conditional. + Instruction *MDFrom = nullptr; + if (NewTrueVal == TrueVal && NewFalseVal == FalseVal) { + MDFrom = &SI; + } + return SelectInst::Create(A, NewTrueVal, NewFalseVal, "", nullptr, + MDFrom); + } // Is (select B, T, F) a SPF? if (CondVal->hasOneUse() && SelType->isIntOrIntVectorTy()) { diff --git a/llvm/test/Transforms/InstCombine/select-and-cmp.ll b/llvm/test/Transforms/InstCombine/select-and-cmp.ll index 50e1493cad5c7..0ac88372c8636 100644 --- a/llvm/test/Transforms/InstCombine/select-and-cmp.ll +++ b/llvm/test/Transforms/InstCombine/select-and-cmp.ll @@ -1,4 +1,4 @@ -; NOTE: Assertions have been autogenerated by utils/update_test_checks.py +; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --check-globals ; RUN: opt < %s -passes=instcombine -S | FileCheck %s define i32 @select_and_icmp(i32 %x, i32 %y, i32 %z) { @@ -114,34 +114,34 @@ define i32 @select_and_icmp_inv(i32 %x, i32 %y, i32 %z) { ; Below used to be negative tests in InstSimplify, but are no more negative cases here -define i32 @select_and_icmp_pred_bad_1(i32 %x, i32 %y, i32 %z) { +define i32 @select_and_icmp_pred_bad_1(i32 %x, i32 %y, i32 %z) !prof !0 { ; CHECK-LABEL: @select_and_icmp_pred_bad_1( -; CHECK-NEXT: ret i32 [[X]] +; CHECK-NEXT: ret i32 [[X:%.*]] ; %A = icmp eq i32 %x, %z %B = icmp ne i32 %y, %z %C = and i1 %A, %B - %D = select i1 %C, i32 %z, i32 %x + %D = select i1 %C, i32 %z, i32 %x, !prof !1 ret i32 %D } -define i32 @select_and_icmp_pred_bad_2(i32 %x, i32 %y, i32 %z) { +define i32 @select_and_icmp_pred_bad_2(i32 %x, i32 %y, i32 %z) !prof !0 { ; CHECK-LABEL: @select_and_icmp_pred_bad_2( ; CHECK-NEXT: [[B:%.*]] = icmp eq i32 [[Y:%.*]], [[Z:%.*]] -; CHECK-NEXT: [[D:%.*]] = select i1 [[B]], i32 [[Z]], i32 [[X]] +; CHECK-NEXT: [[D:%.*]] = select i1 [[B]], i32 [[Z]], i32 [[X:%.*]] ; CHECK-NEXT: ret i32 [[D]] ; %A = icmp ne i32 %x, %z %B = icmp eq i32 %y, %z %C = and i1 %A, %B - %D = select i1 %C, i32 %z, i32 %x + %D = select i1 %C, i32 %z, i32 %x, !prof !1 ret i32 %D } define i32 @select_and_icmp_pred_bad_3(i32 %x, i32 %y, i32 %z) { ; CHECK-LABEL: @select_and_icmp_pred_bad_3( -; CHECK-NEXT: [[B_NOT:%.*]] = icmp eq i32 [[Y:%.*]], [[Z]] -; CHECK-NEXT: [[D:%.*]] = select i1 [[B_NOT]], i32 [[X]], i32 [[Z]] +; CHECK-NEXT: [[B_NOT:%.*]] = icmp eq i32 [[Y:%.*]], [[Z:%.*]] +; CHECK-NEXT: [[D:%.*]] = select i1 [[B_NOT]], i32 [[X:%.*]], i32 [[Z]] ; CHECK-NEXT: ret i32 [[D]] ; %A = icmp ne i32 %x, %z @@ -153,8 +153,8 @@ define i32 @select_and_icmp_pred_bad_3(i32 %x, i32 %y, i32 %z) { define i32 @select_and_icmp_pred_bad_4(i32 %x, i32 %y, i32 %z) { ; CHECK-LABEL: @select_and_icmp_pred_bad_4( -; CHECK-NEXT: [[B:%.*]] = icmp eq i32 [[Y:%.*]], [[Z]] -; CHECK-NEXT: [[D:%.*]] = select i1 [[B]], i32 [[Z]], i32 [[X]] +; CHECK-NEXT: [[B:%.*]] = icmp eq i32 [[Y:%.*]], [[Z:%.*]] +; CHECK-NEXT: [[D:%.*]] = select i1 [[B]], i32 [[Z]], i32 [[X:%.*]] ; CHECK-NEXT: ret i32 [[D]] ; %A = icmp eq i32 %x, %z @@ -166,7 +166,7 @@ define i32 @select_and_icmp_pred_bad_4(i32 %x, i32 %y, i32 %z) { define i32 @select_and_icmp_alt_bad_1(i32 %x, i32 %y, i32 %z) { ; CHECK-LABEL: @select_and_icmp_alt_bad_1( -; CHECK-NEXT: ret i32 [[Z]] +; CHECK-NEXT: ret i32 [[Z:%.*]] ; %A = icmp eq i32 %x, %z %B = icmp ne i32 %y, %z @@ -177,8 +177,8 @@ define i32 @select_and_icmp_alt_bad_1(i32 %x, i32 %y, i32 %z) { define i32 @select_and_icmp_alt_bad_2(i32 %x, i32 %y, i32 %z) { ; CHECK-LABEL: @select_and_icmp_alt_bad_2( -; CHECK-NEXT: [[B:%.*]] = icmp eq i32 [[Y:%.*]], [[Z]] -; CHECK-NEXT: [[D:%.*]] = select i1 [[B]], i32 [[X]], i32 [[Z]] +; CHECK-NEXT: [[B:%.*]] = icmp eq i32 [[Y:%.*]], [[Z:%.*]] +; CHECK-NEXT: [[D:%.*]] = select i1 [[B]], i32 [[X:%.*]], i32 [[Z]] ; CHECK-NEXT: ret i32 [[D]] ; %A = icmp ne i32 %x, %z @@ -191,8 +191,8 @@ define i32 @select_and_icmp_alt_bad_2(i32 %x, i32 %y, i32 %z) { define i32 @select_and_icmp_alt_bad_3(i32 %x, i32 %y, i32 %z) { ; CHECK-LABEL: @select_and_icmp_alt_bad_3( -; CHECK-NEXT: [[B_NOT:%.*]] = icmp eq i32 [[Y:%.*]], [[Z]] -; CHECK-NEXT: [[D:%.*]] = select i1 [[B_NOT]], i32 [[Z]], i32 [[X]] +; CHECK-NEXT: [[B_NOT:%.*]] = icmp eq i32 [[Y:%.*]], [[Z:%.*]] +; CHECK-NEXT: [[D:%.*]] = select i1 [[B_NOT]], i32 [[Z]], i32 [[X:%.*]] ; CHECK-NEXT: ret i32 [[D]] ; %A = icmp ne i32 %x, %z @@ -204,8 +204,8 @@ define i32 @select_and_icmp_alt_bad_3(i32 %x, i32 %y, i32 %z) { define i32 @select_and_icmp_alt_bad_4(i32 %x, i32 %y, i32 %z) { ; CHECK-LABEL: @select_and_icmp_alt_bad_4( -; CHECK-NEXT: [[B:%.*]] = icmp eq i32 [[Y:%.*]], [[Z]] -; CHECK-NEXT: [[D:%.*]] = select i1 [[B]], i32 [[X]], i32 [[Z]] +; CHECK-NEXT: [[B:%.*]] = icmp eq i32 [[Y:%.*]], [[Z:%.*]] +; CHECK-NEXT: [[D:%.*]] = select i1 [[B]], i32 [[X:%.*]], i32 [[Z]] ; CHECK-NEXT: ret i32 [[D]] ; %A = icmp eq i32 %x, %z @@ -322,3 +322,10 @@ define i32 @select_and_icmp_alt_bad_false_val(i32 %x, i32 %y, i32 %z, i32 %k) { %D = select i1 %C, i32 %x, i32 %k ret i32 %D } + +!0 = !{!"function_entry_count", i64 1000} +!1 = !{!"branch_weights", i32 2, i32 3} + +;. +; CHECK: [[META0:![0-9]+]] = !{!"function_entry_count", i64 1000} +;. diff --git a/llvm/test/Transforms/InstCombine/select-and-or.ll b/llvm/test/Transforms/InstCombine/select-and-or.ll index 453ca666a7477..65e8500a5257b 100644 --- a/llvm/test/Transforms/InstCombine/select-and-or.ll +++ b/llvm/test/Transforms/InstCombine/select-and-or.ll @@ -1348,3 +1348,6 @@ define i8 @test_logical_commuted_and_ne_a_b(i1 %other_cond, i8 %a, i8 %b) { %select = select i1 %or.cond, i8 %a, i8 %b ret i8 %select } + +!0 = !{!"function_entry_count", i64 1000} +!1 = !{!"branch_weights", i32 2, i32 3} diff --git a/llvm/test/Transforms/InstCombine/select-or-cmp.ll b/llvm/test/Transforms/InstCombine/select-or-cmp.ll index 72a3747c5e405..82b069bc91e88 100644 --- a/llvm/test/Transforms/InstCombine/select-or-cmp.ll +++ b/llvm/test/Transforms/InstCombine/select-or-cmp.ll @@ -1,4 +1,4 @@ -; NOTE: Assertions have been autogenerated by utils/update_test_checks.py +; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --check-globals ; RUN: opt < %s -passes=instcombine -S | FileCheck %s define i32 @select_or_icmp(i32 %x, i32 %y, i32 %z) { @@ -114,47 +114,47 @@ define i32 @select_or_icmp_inv(i32 %x, i32 %y, i32 %z) { ; Below used to be negative tests in InstSimplify, but are no more negative cases here -define i32 @select_and_icmp_pred_bad_1(i32 %x, i32 %y, i32 %z) { +define i32 @select_and_icmp_pred_bad_1(i32 %x, i32 %y, i32 %z) !prof !0 { ; CHECK-LABEL: @select_and_icmp_pred_bad_1( -; CHECK-NEXT: [[B_NOT:%.*]] = icmp eq i32 [[Y:%.*]], [[Z]] -; CHECK-NEXT: [[D:%.*]] = select i1 [[B_NOT]], i32 [[X]], i32 [[Z]] +; CHECK-NEXT: [[B_NOT:%.*]] = icmp eq i32 [[Y:%.*]], [[Z:%.*]] +; CHECK-NEXT: [[D:%.*]] = select i1 [[B_NOT]], i32 [[X:%.*]], i32 [[Z]], !prof [[PROF1:![0-9]+]] ; CHECK-NEXT: ret i32 [[D]] ; %A = icmp eq i32 %x, %z %B = icmp ne i32 %y, %z %C = or i1 %A, %B - %D = select i1 %C, i32 %z, i32 %x + %D = select i1 %C, i32 %z, i32 %x, !prof !1 ret i32 %D } -define i32 @select_and_icmp_pred_bad_2(i32 %x, i32 %y, i32 %z) { +define i32 @select_and_icmp_pred_bad_2(i32 %x, i32 %y, i32 %z) !prof !0 { ; CHECK-LABEL: @select_and_icmp_pred_bad_2( -; CHECK-NEXT: ret i32 [[Z]] +; CHECK-NEXT: ret i32 [[Z:%.*]] ; %A = icmp ne i32 %x, %z %B = icmp eq i32 %y, %z %C = or i1 %A, %B - %D = select i1 %C, i32 %z, i32 %x + %D = select i1 %C, i32 %z, i32 %x, !prof !1 ret i32 %D } -define i32 @select_and_icmp_pred_bad_3(i32 %x, i32 %y, i32 %z) { +define i32 @select_and_icmp_pred_bad_3(i32 %x, i32 %y, i32 %z) !prof !0 { ; CHECK-LABEL: @select_and_icmp_pred_bad_3( -; CHECK-NEXT: [[B:%.*]] = icmp eq i32 [[Y:%.*]], [[Z]] -; CHECK-NEXT: [[D:%.*]] = select i1 [[B]], i32 [[Z]], i32 [[X]] +; CHECK-NEXT: [[B:%.*]] = icmp eq i32 [[Y:%.*]], [[Z:%.*]] +; CHECK-NEXT: [[D:%.*]] = select i1 [[B]], i32 [[Z]], i32 [[X:%.*]], !prof [[PROF2:![0-9]+]] ; CHECK-NEXT: ret i32 [[D]] ; %A = icmp eq i32 %x, %z %B = icmp eq i32 %y, %z %C = or i1 %A, %B - %D = select i1 %C, i32 %z, i32 %x + %D = select i1 %C, i32 %z, i32 %x, !prof !1 ret i32 %D } define i32 @select_and_icmp_pred_bad_4(i32 %x, i32 %y, i32 %z) { ; CHECK-LABEL: @select_and_icmp_pred_bad_4( -; CHECK-NEXT: [[B_NOT:%.*]] = icmp eq i32 [[Y:%.*]], [[Z]] -; CHECK-NEXT: [[D:%.*]] = select i1 [[B_NOT]], i32 [[X]], i32 [[Z]] +; CHECK-NEXT: [[B_NOT:%.*]] = icmp eq i32 [[Y:%.*]], [[Z:%.*]] +; CHECK-NEXT: [[D:%.*]] = select i1 [[B_NOT]], i32 [[X:%.*]], i32 [[Z]] ; CHECK-NEXT: ret i32 [[D]] ; %A = icmp ne i32 %x, %z @@ -166,8 +166,8 @@ define i32 @select_and_icmp_pred_bad_4(i32 %x, i32 %y, i32 %z) { define i32 @select_or_icmp_alt_bad_1(i32 %x, i32 %y, i32 %z) { ; CHECK-LABEL: @select_or_icmp_alt_bad_1( -; CHECK-NEXT: [[B_NOT:%.*]] = icmp eq i32 [[Y:%.*]], [[Z]] -; CHECK-NEXT: [[D:%.*]] = select i1 [[B_NOT]], i32 [[Z]], i32 [[X]] +; CHECK-NEXT: [[B_NOT:%.*]] = icmp eq i32 [[Y:%.*]], [[Z:%.*]] +; CHECK-NEXT: [[D:%.*]] = select i1 [[B_NOT]], i32 [[Z]], i32 [[X:%.*]] ; CHECK-NEXT: ret i32 [[D]] ; %A = icmp eq i32 %x, %z @@ -179,7 +179,7 @@ define i32 @select_or_icmp_alt_bad_1(i32 %x, i32 %y, i32 %z) { define i32 @select_or_icmp_alt_bad_2(i32 %x, i32 %y, i32 %z) { ; CHECK-LABEL: @select_or_icmp_alt_bad_2( -; CHECK-NEXT: ret i32 [[X]] +; CHECK-NEXT: ret i32 [[X:%.*]] ; %A = icmp ne i32 %x, %z %B = icmp eq i32 %y, %z @@ -190,8 +190,8 @@ define i32 @select_or_icmp_alt_bad_2(i32 %x, i32 %y, i32 %z) { define i32 @select_or_icmp_alt_bad_3(i32 %x, i32 %y, i32 %z) { ; CHECK-LABEL: @select_or_icmp_alt_bad_3( -; CHECK-NEXT: [[B:%.*]] = icmp eq i32 [[Y:%.*]], [[Z]] -; CHECK-NEXT: [[D:%.*]] = select i1 [[B]], i32 [[X]], i32 [[Z]] +; CHECK-NEXT: [[B:%.*]] = icmp eq i32 [[Y:%.*]], [[Z:%.*]] +; CHECK-NEXT: [[D:%.*]] = select i1 [[B]], i32 [[X:%.*]], i32 [[Z]] ; CHECK-NEXT: ret i32 [[D]] ; %A = icmp eq i32 %x, %z @@ -203,8 +203,8 @@ define i32 @select_or_icmp_alt_bad_3(i32 %x, i32 %y, i32 %z) { define i32 @select_or_icmp_alt_bad_4(i32 %x, i32 %y, i32 %z) { ; CHECK-LABEL: @select_or_icmp_alt_bad_4( -; CHECK-NEXT: [[B_NOT:%.*]] = icmp eq i32 [[Y:%.*]], [[Z]] -; CHECK-NEXT: [[D:%.*]] = select i1 [[B_NOT]], i32 [[Z]], i32 [[X]] +; CHECK-NEXT: [[B_NOT:%.*]] = icmp eq i32 [[Y:%.*]], [[Z:%.*]] +; CHECK-NEXT: [[D:%.*]] = select i1 [[B_NOT]], i32 [[Z]], i32 [[X:%.*]] ; CHECK-NEXT: ret i32 [[D]] ; %A = icmp ne i32 %x, %z @@ -321,3 +321,11 @@ define i32 @select_or_icmp_alt_bad_false_val(i32 %x, i32 %y, i32 %z, i32 %k) { %D = select i1 %C, i32 %x, i32 %k ret i32 %D } + +!0 = !{!"function_entry_count", i64 1000} +!1 = !{!"branch_weights", i32 2, i32 3} +;. +; CHECK: [[META0:![0-9]+]] = !{!"function_entry_count", i64 1000} +; CHECK: [[PROF1]] = !{!"branch_weights", i32 3, i32 2} +; CHECK: [[PROF2]] = !{!"branch_weights", i32 2, i32 3} +;. |
mtrofin reviewed Sep 24, 2025
mtrofin approved these changes Sep 24, 2025
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| Reverted to unbreak the CI, feel free to reland with a fix! |
llvm-sync bot pushed a commit to arm/arm-toolchain that referenced this pull request Oct 3, 2025
…t instructions with conditionals" (#161885) Reverts llvm/llvm-project#159666 Many bots are broken right now.
alanzhao1 added a commit to alanzhao1/llvm-project that referenced this pull request Oct 3, 2025
…ions with conditionals" (llvm#161885) This reverts commit 572b579. This is a reland of llvm#159666 but with a fix moving the `extern` declaration of the flag under the LLVM namespace, which is needed to fix a linker error caused by llvm#161240.
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If
selectsimplification produces the transform:or
it stands to reason that if the branches are the same, then the branch weights remain the same since the net effect is a simplification of the conditional.
There are also cases where InstCombine negates the conditional (and therefore reverses the branches); this PR asserts that the branch weights are reversed in this case.
Tracking issue: #147390