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[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
This commit is contained in:
Sanjay Patel 2019-11-15 16:06:43 -05:00
parent 782392db81
commit ee0882bdf8
2 changed files with 8 additions and 2 deletions
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8
llvm/lib/Transforms/Utils/SimplifyCFG.cpp
View File

@ -1404,10 +1404,16 @@ HoistTerminator:
// These values do not agree. Insert a select instruction before NT // These values do not agree. Insert a select instruction before NT
// that determines the right value. // that determines the right value.
SelectInst *&SI = InsertedSelects[std::make_pair(BB1V, BB2V)]; 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>( SI = cast<SelectInst>(
Builder.CreateSelect(BI->getCondition(), BB1V, BB2V, Builder.CreateSelect(BI->getCondition(), BB1V, BB2V,
BB1V->getName() + "." + BB2V->getName(), BI)); BB1V->getName() + "." + BB2V->getName(), BI));
}
// Make the PHI node use the select for all incoming values for BB1/BB2 // Make the PHI node use the select for all incoming values for BB1/BB2
for (unsigned i = 0, e = PN.getNumIncomingValues(); i != e; ++i) for (unsigned i = 0, e = PN.getNumIncomingValues(); i != e; ++i)

2
llvm/test/Transforms/SimplifyCFG/HoistCode.ll
View File

@ -19,7 +19,7 @@ define float @PR39535min(float %x) {
; CHECK-LABEL: @PR39535min( ; CHECK-LABEL: @PR39535min(
; CHECK-NEXT: entry: ; CHECK-NEXT: entry:
; CHECK-NEXT: [[TOBOOL:%.*]] = fcmp une float [[X:%.*]], 0.000000e+00 ; 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]] ; CHECK-NEXT: ret float [[DOTX]]
; ;
entry: entry: