[IR] allow fast-math-flags on phi of FP values

The changes here are based on the corresponding diffs for allowing FMF on 'select':
D61917

As discussed there, we want to have fast-math-flags be a property of an FP value
because the alternative (having them on things like fcmp) leads to logical
inconsistency such as:
https://bugs.llvm.org/show_bug.cgi?id=38086

The earlier patch for select made almost no practical difference because most
unoptimized conditional code begins life as a phi (based on what I see in clang).
Similarly, I don't expect this patch to do much on its own either because
SimplifyCFG promptly drops the flags when converting to select on a minimal
example like:
https://bugs.llvm.org/show_bug.cgi?id=39535

But once we have this plumbing in place, we should be able to wire up the FMF
propagation and start solving cases like that.

The change to RecurrenceDescriptor::AddReductionVar() is required to prevent a
regression in a LoopVectorize test. We are intersecting the FMF of any
FPMathOperator there, so if a phi is not properly annotated, new math
instructions may not be either. Once we fix the propagation in SimplifyCFG, it
may be safe to remove that hack.

Differential Revision: https://reviews.llvm.org/D67564

llvm-svn: 372866

1 files changed, 5 insertions, 2 deletions

diff --git a/llvm/unittests/IR/InstructionsTest.cpp b/llvm/unittests/IR/InstructionsTest.cpp
index b2ea3844d33..afd579400ff 100644
--- a/llvm/unittests/IR/InstructionsTest.cpp
+++ b/llvm/unittests/IR/InstructionsTest.cpp
@@ -1034,13 +1034,16 @@ TEST(InstructionsTest, SkipDebug) {
   EXPECT_EQ(nullptr, Term->getNextNonDebugInstruction());
 }
 
-TEST(InstructionsTest, PhiIsNotFPMathOperator) {
+TEST(InstructionsTest, PhiMightNotBeFPMathOperator) {
   LLVMContext Context;
   IRBuilder<> Builder(Context);
   MDBuilder MDHelper(Context);
-  Instruction *I = Builder.CreatePHI(Builder.getDoubleTy(), 0);
+  Instruction *I = Builder.CreatePHI(Builder.getInt32Ty(), 0);
   EXPECT_FALSE(isa<FPMathOperator>(I));
   I->deleteValue();
+  Instruction *FP = Builder.CreatePHI(Builder.getDoubleTy(), 0);
+  EXPECT_TRUE(isa<FPMathOperator>(FP));
+  FP->deleteValue();
 }
 
 TEST(InstructionsTest, FNegInstruction) {