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[SLPVectorizer] Vectorizing the libm sqrt to llvm's sqrt intrinsic requires nnan

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To quote the langref "Unlike sqrt in libm, however, llvm.sqrt has
undefined behavior for negative numbers other than -0.0 (which allows
for better optimization, because there is no need to worry about errno
being set). llvm.sqrt(-0.0) is defined to return -0.0 like IEEE sqrt."

This means that it's unsafe to replace sqrt with llvm.sqrt unless the
call is annotated with nnan.

Thanks to Hal Finkel for pointing this out!

llvm-svn: 265521
This commit is contained in:
David Majnemer 2016-04-06 07:04:53 +00:00
parent fa81f42d1e
commit 52bda94846
3 changed files with 30 additions and 4 deletions
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2
lib/Analysis/VectorUtils.cpp
View File

@ -223,7 +223,9 @@ Intrinsic::ID llvm::getIntrinsicIDForCall(CallInst *CI,
case LibFunc::sqrt:
case LibFunc::sqrtf:
case LibFunc::sqrtl:
if (CI->hasNoNaNs())
return checkUnaryFloatSignature(*CI, Intrinsic::sqrt);
return Intrinsic::not_intrinsic;
}
return Intrinsic::not_intrinsic;

26
test/Transforms/LoopVectorize/X86/veclib-calls.ll
View File

@ -3,6 +3,31 @@
target datalayout = "e-p:64:64:64-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:64:64-f32:32:32-f64:64:64-v64:64:64-v128:128:128-a0:0:64-s0:64:64-f80:128:128-n8:16:32:64-S128"
target triple = "x86_64-unknown-linux-gnu"
;CHECK-LABEL: @sqrt_f32(
;CHECK: vsqrtf{{.*}}<4 x float>
;CHECK: ret void
declare float @sqrtf(float) nounwind readnone
define void @sqrt_f32(i32 %n, float* noalias %y, float* noalias %x) nounwind uwtable {
entry:
%cmp6 = icmp sgt i32 %n, 0
br i1 %cmp6, label %for.body, label %for.end
for.body: ; preds = %entry, %for.body
%indvars.iv = phi i64 [ %indvars.iv.next, %for.body ], [ 0, %entry ]
%arrayidx = getelementptr inbounds float, float* %y, i64 %indvars.iv
%0 = load float, float* %arrayidx, align 4
%call = tail call float @sqrtf(float %0) nounwind readnone
%arrayidx2 = getelementptr inbounds float, float* %x, i64 %indvars.iv
store float %call, float* %arrayidx2, align 4
%indvars.iv.next = add i64 %indvars.iv, 1
%lftr.wideiv = trunc i64 %indvars.iv.next to i32
%exitcond = icmp eq i32 %lftr.wideiv, %n
br i1 %exitcond, label %for.end, label %for.body
for.end: ; preds = %for.body, %entry
ret void
}
;CHECK-LABEL: @exp_f32(
;CHECK: vexpf{{.*}}<4 x float>
;CHECK: ret void
@ -135,7 +160,6 @@ for.end: ; preds = %for.body, %entry
;CHECK-LABEL: @sqrt_f32_nobuiltin(
;CHECK-NOT: vsqrtf{{.*}}<4 x float>
;CHECK: ret void
declare float @sqrtf(float) nounwind readnone
define void @sqrt_f32_nobuiltin(i32 %n, float* noalias %y, float* noalias %x) nounwind uwtable {
entry:
%cmp6 = icmp sgt i32 %n, 0

4
test/Transforms/SLPVectorizer/X86/call.ll
View File

@ -105,13 +105,13 @@ entry:
%i0 = load double, double* %a, align 8
%i1 = load double, double* %b, align 8
%mul = fmul double %i0, %i1
%call = tail call double @sqrt(double %mul) nounwind readnone
%call = tail call nnan double @sqrt(double %mul) nounwind readnone
%arrayidx3 = getelementptr inbounds double, double* %a, i64 1
%i3 = load double, double* %arrayidx3, align 8
%arrayidx4 = getelementptr inbounds double, double* %b, i64 1
%i4 = load double, double* %arrayidx4, align 8
%mul5 = fmul double %i3, %i4
%call5 = tail call double @sqrt(double %mul5) nounwind readnone
%call5 = tail call nnan double @sqrt(double %mul5) nounwind readnone
store double %call, double* %c, align 8
%arrayidx5 = getelementptr inbounds double, double* %c, i64 1
store double %call5, double* %arrayidx5, align 8