[PATCH] D28405: SimplifyLibCalls: Replace fabs libcalls with intrinsics

Eli Friedman via Phabricator via llvm-commits llvm-commits at lists.llvm.org
Mon Jan 16 13:43:02 PST 2017

efriedma added inline comments.

Comment at: lib/Transforms/InstCombine/InstCombineCalls.cpp:1644
+                                           { ExtSrc->getType() });
+      Value *NewFabs = Builder->CreateCall(F, ExtSrc);
+      NewFabs->takeName(II);
efriedma wrote:
> Fast-math flags?
Fast-math flags?

Comment at: test/Transforms/InstCombine/fabs.ll:16
 ; CHECK-NEXT: %mul = fmul float %x, %x
-; CHECK-NEXT: %fabsf = tail call float @fabsf(float %mul)
+; CHECK-NEXT: %fabsf = call float @llvm.fabs.f32(float %mul)
 ; CHECK-NEXT: ret float %fabsf
arsenm wrote:
> arsenm wrote:
> > efriedma wrote:
> > > efriedma wrote:
> > > > This is probably going to fail on Windows... maybe change the test to call llvm.fabs rather than fabs?
> > > Still probably going to fail on Windows, where fabsf() doesn't exist.
> > Do you mean the intrinsic won't work? I would expect codegen to promote it
> It looks like a fabs instruction is emitted for the intrinsic
No... I mean we call `TLI.setUnavailable(LibFunc::fabsf);` on Windows, so it isn't a library call, so we'll never call optimizeFabs.


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