[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, 1 insertions, 1 deletions

diff --git a/llvm/lib/CodeGen/CodeGenPrepare.cpp b/llvm/lib/CodeGen/CodeGenPrepare.cpp
index b3a6e284f4f..0333232983d 100644
--- a/llvm/lib/CodeGen/CodeGenPrepare.cpp
+++ b/llvm/lib/CodeGen/CodeGenPrepare.cpp
@@ -5951,7 +5951,7 @@ bool CodeGenPrepare::optimizeSelectInst(SelectInst *SI) {
   // If branch conversion isn't desirable, exit early.
   if (DisableSelectToBranch || OptSize || !TLI)
     return false;
-
+TLI->isSelectSupported(<#SelectSupportKind#>)
   // Find all consecutive select instructions that share the same condition.
   SmallVector<SelectInst *, 2> ASI;
   ASI.push_back(SI);