From 491284f0da18d31bd982619868f96b4fe6fb8b16 Mon Sep 17 00:00:00 2001
From: Vyacheslav Klochkov <vyacheslav.n.klochkov@gmail.com>
Date: Tue, 22 Nov 2016 20:23:04 +0000
Subject: [PATCH] Fixed the lost FastMathFlags in Reassociate optimization.
 Reviewer: Hal Finkel. Differential Revision: https://reviews.llvm.org/D26957

llvm-svn: 287695
---
 lib/Transforms/Scalar/Reassociate.cpp          |  6 ++++++
 test/Transforms/Reassociate/propagate-flags.ll | 14 ++++++++++++++
 2 files changed, 20 insertions(+)
 create mode 100644 test/Transforms/Reassociate/propagate-flags.ll

diff --git a/lib/Transforms/Scalar/Reassociate.cpp b/lib/Transforms/Scalar/Reassociate.cpp
index 40c1e3717a2..181a324861e 100644
--- a/lib/Transforms/Scalar/Reassociate.cpp
+++ b/lib/Transforms/Scalar/Reassociate.cpp
@@ -1778,6 +1778,12 @@ Value *ReassociatePass::OptimizeMul(BinaryOperator *I,
     return nullptr; // All distinct factors, so nothing left for us to do.
 
   IRBuilder<> Builder(I);
+  // The reassociate transformation for FP operations is performed only
+  // if unsafe algebra is permitted by FastMathFlags. Propagate those flags
+  // to the newly generated operations.
+  if (auto FPI = dyn_cast<FPMathOperator>(I))
+    Builder.setFastMathFlags(FPI->getFastMathFlags());
+
   Value *V = buildMinimalMultiplyDAG(Builder, Factors);
   if (Ops.empty())
     return V;
diff --git a/test/Transforms/Reassociate/propagate-flags.ll b/test/Transforms/Reassociate/propagate-flags.ll
new file mode 100644
index 00000000000..b8987855f0e
--- /dev/null
+++ b/test/Transforms/Reassociate/propagate-flags.ll
@@ -0,0 +1,14 @@
+; RUN: opt < %s -reassociate -S | FileCheck %s
+ 
+; CHECK-LABEL: func
+; CHECK:       fmul fast double
+; CHECK-NEXT:  fmul fast double
+; CHECK-NEXT:  ret
+
+define double @func(double %a, double %b) {
+entry:
+  %mul1 = fmul fast double %a, %a
+  %mul2 = fmul fast double %b, %b
+  %mul3 = fmul fast double %mul1, %mul2
+  ret double %mul3
+}