Commit ee0882bd authored by Sanjay Patel's avatar Sanjay Patel
Browse files

[SimplifyCFG] propagate fast-math-flags (FMF) from phi to select 

This is another step towards having FMF apply only to FP values
rather than those + fcmp. See PR38086 for one of the original
discussions/motivations:
https://bugs.llvm.org/show_bug.cgi?id=38086

And the test here is derived from PR39535:
https://bugs.llvm.org/show_bug.cgi?id=39535

Currently, we lose FMF when converting any phi to select in
SimplifyCFG. There are a small number of similar changes needed
to correct within SimplifyCFG, so it should be quick to patch
this pass up.

FMF was extended to select and phi with:
D61917
D67564

Differential Revision: https://reviews.llvm.org/D70208
parent 782392db

llvm/lib/Transforms/Utils/SimplifyCFG.cpp

+7 −1
Original line number Diff line number Diff line
@@ -1404,10 +1404,16 @@ HoistTerminator: 
      // These values do not agree.  Insert a select instruction before NT

      // that determines the right value.

      SelectInst *&SI = InsertedSelects[std::make_pair(BB1V, BB2V)];

      if (!SI)

      if (!SI) {

        // Propagate fast-math-flags from phi node to its replacement select.

        IRBuilder<>::FastMathFlagGuard FMFGuard(Builder);

        if (isa<FPMathOperator>(PN))

          Builder.setFastMathFlags(PN.getFastMathFlags());



        SI = cast<SelectInst>(

            Builder.CreateSelect(BI->getCondition(), BB1V, BB2V,

                                 BB1V->getName() + "." + BB2V->getName(), BI));

      }



      // Make the PHI node use the select for all incoming values for BB1/BB2

      for (unsigned i = 0, e = PN.getNumIncomingValues(); i != e; ++i)

llvm/test/Transforms/SimplifyCFG/HoistCode.ll

+1 −1
Original line number Diff line number Diff line
@@ -19,7 +19,7 @@ define float @PR39535min(float %x) { 
; CHECK-LABEL: @PR39535min(

; CHECK-NEXT:  entry:

; CHECK-NEXT:    [[TOBOOL:%.*]] = fcmp une float [[X:%.*]], 0.000000e+00

; CHECK-NEXT:    [[DOTX:%.*]] = select i1 [[TOBOOL]], float 0.000000e+00, float [[X]]

; CHECK-NEXT:    [[DOTX:%.*]] = select fast i1 [[TOBOOL]], float 0.000000e+00, float [[X]]

; CHECK-NEXT:    ret float [[DOTX]]

;

entry: