From ee0882bdf866ad8877dfda3820a822c851d0733a Mon Sep 17 00:00:00 2001 From: Sanjay Patel Date: Fri, 15 Nov 2019 16:06:43 -0500 Subject: [PATCH] [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 --- llvm/lib/Transforms/Utils/SimplifyCFG.cpp | 8 +++++++- llvm/test/Transforms/SimplifyCFG/HoistCode.ll | 2 +- 2 files changed, 8 insertions(+), 2 deletions(-) diff --git a/llvm/lib/Transforms/Utils/SimplifyCFG.cpp b/llvm/lib/Transforms/Utils/SimplifyCFG.cpp index 9644ba3..ab1a474 100644 --- a/llvm/lib/Transforms/Utils/SimplifyCFG.cpp +++ b/llvm/lib/Transforms/Utils/SimplifyCFG.cpp @@ -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(PN)) + Builder.setFastMathFlags(PN.getFastMathFlags()); + SI = cast( 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) diff --git a/llvm/test/Transforms/SimplifyCFG/HoistCode.ll b/llvm/test/Transforms/SimplifyCFG/HoistCode.ll index 1fb9c46..575cb4f 100644 --- a/llvm/test/Transforms/SimplifyCFG/HoistCode.ll +++ b/llvm/test/Transforms/SimplifyCFG/HoistCode.ll @@ -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: -- 2.7.4