Getting the name of the function in a CallInst

Question

I am currently doing a static analysis, on opencl code(.cl). I used clang(clang -S -emit-llvm foo.cl) to create a SSA-form LLVM-IR, and gave that as an input for llvm framework.

In the .ll file, there is a function call which looks like below,

%call = tail call i32 (i32, ...) bitcast (i32 (...)* @get_global_id to i32 (i32, ...)*)(i32 0) #2 %cmp = icmp slt i32 %call, %num_elements ....

I want to get the name of the function (get_global_id) of the function call. I tried to get the function with the

Value * CallInst::getCalledValue ();

But since, the IR file has no linking information of the function of get_global_id(), it seems to return NULL.(Since there is no actuall body of the function defined in the .cl file). What should be the delicate way to get the name of the function in this case?

Below is the whole source code

__kernel void convolution(__global int* input, __constant int* mask, __global int* output, int num_elements, int width, int mask_width) { int gid = get_global_id(0); if (gid >= num_elements) return; int tx = gid % width; int ty = gid / width; int offset = mask_width/2; if (tx < offset || ty < offset || tx >= (width-offset) || ty >= (width-offset)) { output[gid] = 0; return; } int sum = 0; int tmpx = tx - offset; int tmpy = ty - offset; for (int r = 0; r < mask_width; ++r) { for (int c = 0; c < mask_width; ++c) { sum += mask[r * mask_width + c] * input[(tmpy + r ) * width + tmpx + c]; } } output[gid] = sum; }

and the .ll file

target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128" target triple = "x86_64-unknown-linux-gnu" ; Function Attrs: nounwind uwtable define void @convolution(i32* nocapture readonly %input, i32* nocapture readonly %mask, i32* nocapture %output, i32 %num_elements, i32 %width, i32 %mask_width) #0 { entry: %call = tail call i32 (i32, ...) bitcast (i32 (...)* @get_global_id to i32 (i32, ...)*)(i32 0) #2 %cmp = icmp slt i32 %call, %num_elements br i1 %cmp, label %if.end, label %cleanup35 if.end: ; preds = %entry %rem = srem i32 %call, %width %div = sdiv i32 %call, %width %div1 = sdiv i32 %mask_width, 2 %cmp2 = icmp slt i32 %rem, %div1 %cmp3 = icmp slt i32 %div, %div1 %or.cond = or i1 %cmp2, %cmp3 br i1 %or.cond, label %if.then9, label %lor.lhs.false4 lor.lhs.false4: ; preds = %if.end %sub = sub nsw i32 %width, %div1 %cmp5 = icmp slt i32 %rem, %sub %cmp8 = icmp slt i32 %div, %sub %or.cond73 = and i1 %cmp5, %cmp8 br i1 %or.cond73, label %if.end10, label %if.then9 if.then9: ; preds = %lor.lhs.false4, %if.end %idxprom = sext i32 %call to i64 %arrayidx = getelementptr inbounds i32, i32* %output, i64 %idxprom store i32 0, i32* %arrayidx, align 4, !tbaa !7 br label %cleanup35 if.end10: ; preds = %lor.lhs.false4 %cmp1377 = icmp sgt i32 %mask_width, 0 br i1 %cmp1377, label %for.cond14.preheader.lr.ph, label %for.cond.cleanup for.cond14.preheader.lr.ph: ; preds = %if.end10 %sub12 = sub i32 %div, %div1 %sub11 = sub i32 %rem, %div1 %0 = sext i32 %mask_width to i64 %1 = sext i32 %sub12 to i64 %2 = sext i32 %width to i64 %3 = sext i32 %sub11 to i64 %xtraiter = and i32 %mask_width, 1 %lcmp.mod = icmp eq i32 %xtraiter, 0 %4 = icmp eq i32 %mask_width, 1 br label %for.body17.lr.ph for.body17.lr.ph: ; preds = %for.cond14.preheader.lr.ph, %for.cond.cleanup16 %indvars.iv84 = phi i64 [ 0, %for.cond14.preheader.lr.ph ], [ %indvars.iv.next85, %for.cond.cleanup16 ] %sum.078 = phi i32 [ 0, %for.cond14.preheader.lr.ph ], [ %add27.lcssa, %for.cond.cleanup16 ] %5 = mul nsw i64 %indvars.iv84, %0 %6 = add nsw i64 %1, %indvars.iv84 %7 = mul nsw i64 %6, %2 %8 = add nsw i64 %3, %7 br i1 %lcmp.mod, label %for.body17.lr.ph.split, label %for.body17.prol for.body17.prol: ; preds = %for.body17.lr.ph %arrayidx19.prol = getelementptr inbounds i32, i32* %mask, i64 %5 %9 = load i32, i32* %arrayidx19.prol, align 4, !tbaa !7 %10 = add i64 %3, %7 %arrayidx25.prol = getelementptr inbounds i32, i32* %input, i64 %10 %11 = load i32, i32* %arrayidx25.prol, align 4, !tbaa !7 %mul26.prol = mul nsw i32 %11, %9 %add27.prol = add nsw i32 %mul26.prol, %sum.078 br label %for.body17.lr.ph.split for.body17.lr.ph.split: ; preds = %for.body17.lr.ph, %for.body17.prol %add27.lcssa.unr = phi i32 [ undef, %for.body17.lr.ph ], [ %add27.prol, %for.body17.prol ] %indvars.iv.unr = phi i64 [ 0, %for.body17.lr.ph ], [ 1, %for.body17.prol ] %sum.175.unr = phi i32 [ %sum.078, %for.body17.lr.ph ], [ %add27.prol, %for.body17.prol ] br i1 %4, label %for.cond.cleanup16, label %for.body17.lr.ph.split.split for.body17.lr.ph.split.split: ; preds = %for.body17.lr.ph.split br label %for.body17 for.cond.cleanup.loopexit: ; preds = %for.cond.cleanup16 %add27.lcssa.lcssa = phi i32 [ %add27.lcssa, %for.cond.cleanup16 ] br label %for.cond.cleanup for.cond.cleanup: ; preds = %for.cond.cleanup.loopexit, %if.end10 %sum.0.lcssa = phi i32 [ 0, %if.end10 ], [ %add27.lcssa.lcssa, %for.cond.cleanup.loopexit ] %idxprom31 = sext i32 %call to i64 %arrayidx32 = getelementptr inbounds i32, i32* %output, i64 %idxprom31 store i32 %sum.0.lcssa, i32* %arrayidx32, align 4, !tbaa !7 br label %cleanup35 for.cond.cleanup16.unr-lcssa: ; preds = %for.body17 %add27.1.lcssa = phi i32 [ %add27.1, %for.body17 ] br label %for.cond.cleanup16 for.cond.cleanup16: ; preds = %for.body17.lr.ph.split, %for.cond.cleanup16.unr-lcssa %add27.lcssa = phi i32 [ %add27.lcssa.unr, %for.body17.lr.ph.split ], [ %add27.1.lcssa, %for.cond.cleanup16.unr-lcssa ] %indvars.iv.next85 = add nuw nsw i64 %indvars.iv84, 1 %lftr.wideiv90 = trunc i64 %indvars.iv.next85 to i32 %exitcond91 = icmp eq i32 %lftr.wideiv90, %mask_width br i1 %exitcond91, label %for.cond.cleanup.loopexit, label %for.body17.lr.ph for.body17: ; preds = %for.body17, %for.body17.lr.ph.split.split %indvars.iv = phi i64 [ %indvars.iv.unr, %for.body17.lr.ph.split.split ], [ %indvars.iv.next.1, %for.body17 ] %sum.175 = phi i32 [ %sum.175.unr, %for.body17.lr.ph.split.split ], [ %add27.1, %for.body17 ] %12 = add nsw i64 %indvars.iv, %5 %arrayidx19 = getelementptr inbounds i32, i32* %mask, i64 %12 %13 = load i32, i32* %arrayidx19, align 4, !tbaa !7 %14 = add nsw i64 %8, %indvars.iv %arrayidx25 = getelementptr inbounds i32, i32* %input, i64 %14 %15 = load i32, i32* %arrayidx25, align 4, !tbaa !7 %mul26 = mul nsw i32 %15, %13 %add27 = add nsw i32 %mul26, %sum.175 %indvars.iv.next = add nuw nsw i64 %indvars.iv, 1 %16 = add nsw i64 %indvars.iv.next, %5 %arrayidx19.1 = getelementptr inbounds i32, i32* %mask, i64 %16 %17 = load i32, i32* %arrayidx19.1, align 4, !tbaa !7 %18 = add nsw i64 %8, %indvars.iv.next %arrayidx25.1 = getelementptr inbounds i32, i32* %input, i64 %18 %19 = load i32, i32* %arrayidx25.1, align 4, !tbaa !7 %mul26.1 = mul nsw i32 %19, %17 %add27.1 = add nsw i32 %mul26.1, %add27 %indvars.iv.next.1 = add nsw i64 %indvars.iv, 2 %lftr.wideiv.1 = trunc i64 %indvars.iv.next.1 to i32 %exitcond.1 = icmp eq i32 %lftr.wideiv.1, %mask_width br i1 %exitcond.1, label %for.cond.cleanup16.unr-lcssa, label %for.body17 cleanup35: ; preds = %if.then9, %for.cond.cleanup, %entry ret void } declare i32 @get_global_id(...) #1 attributes #0 = { nounwind uwtable "disable-tail-calls"="false" "less-precise-fpmad"="false" "no-frame-pointer-elim"="true" "no-frame-pointer-elim-non-leaf" "no-infs-fp-math"="false" "no-nans-fp-math"="false" "stack-protector-buffer-size"="8" "target-cpu"="x86-64" "target-features"="+fxsr,+mmx,+sse,+sse2" "unsafe-fp-math"="false" "use-soft-float"="false" } attributes #1 = { "disable-tail-calls"="false" "less-precise-fpmad"="false" "no-frame-pointer-elim"="true" "no-frame-pointer-elim-non-leaf" "no-infs-fp-math"="false" "no-nans-fp-math"="false" "stack-protector-buffer-size"="8" "target-cpu"="x86-64" "target-features"="+fxsr,+mmx,+sse,+sse2" "unsafe-fp-math"="false" "use-soft-float"="false" } attributes #2 = { nounwind } !opencl.kernels = !{!0} !llvm.ident = !{!6} !0 = !{void (i32*, i32*, i32*, i32, i32, i32)* @convolution, !1, !2, !3, !4, !5} !1 = !{!"kernel_arg_addr_space", i32 0, i32 0, i32 0, i32 0, i32 0, i32 0} !2 = !{!"kernel_arg_access_qual", !"none", !"none", !"none", !"none", !"none", !"none"} !3 = !{!"kernel_arg_type", !"int*", !"int*", !"int*", !"int", !"int", !"int"} !4 = !{!"kernel_arg_base_type", !"int*", !"int*", !"int*", !"int", !"int", !"int"} !5 = !{!"kernel_arg_type_qual", !"", !"const", !"", !"", !"", !""} !6 = !{!"clang version 3.8.0 (trunk 253973)"} !7 = !{!8, !8, i64 0} !8 = !{!"int", !9, i64 0} !9 = !{!"omnipotent char", !10, i64 0} !10 = !{!"Simple C/C++ TBAA"}

And in my project, I'm using it like...

.... InstListType & inst_list = b.getInstList(); InstListType::iterator inst_it; for(inst_it = inst_list.begin(); inst_it != inst_list.end() ; inst_it++) { Instruction & inst = *inst_it; switch(inst.getOpcode()) { case Instruction::Call: CallInst* ci ; ci = (CallInst*)&inst; //Memory access error here since getCalledFunction returns NULL std::cout<<ci->getCalledFunction()->getName().str()<<std::endl; ....

I'd expect getCalledFunction to return null, but not getCalledValue. Are you sure this is what happened? Do you have code you can post (+ input file)? — Ismail Badawi
– Ismail Badawi, Commented Dec 1, 2015 at 1:18
@IsmailBadawi I'm not 100% sure, but there was no other explanation for me. As you said, getCalledValue returns something, but getCalledValue()->getName().str() seems to return an empty string "" — izazu
– izazu, Commented Dec 1, 2015 at 9:46

Ismail Badawi · Accepted Answer · 2015-12-01 10:48:17Z

The signature of get_global_id in the IR is

declare i32 @get_global_id(...) #1

and at the call site, there's a constant cast expression:

%call = tail call i32 (i32, ...) bitcast (i32 (...)* @get_global_id to i32 (i32, ...)*)(i32 0) #2

I think this happens because the C code is missing a declaration for get_global_id. If you can't change the code to add an extern declaration with the right signature (I'm not familiar with OpenCL so it might be common not to have declarations for those), then what you can do is just strip the casts away before looking for a name, like this:

if (Function *Callee = dyn_cast<Function>(ci->getCalledValue()->stripPointerCasts())) { // Callee->getName() should be "get_global_id" }

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