[LoopUtils][SLPVectorizer] clean up management of fast-math-flags

Instead of passing around fast-math-flags as a parameter, we can set those
using an IRBuilder guard object. This is no-functional-change-intended.

The motivation is to eventually fix the vectorizers to use and set the
correct fast-math-flags for reductions. Examples of that not behaving as
expected are:
https://bugs.llvm.org/show_bug.cgi?id=23116 (should be able to reduce with less than 'fast')
https://bugs.llvm.org/show_bug.cgi?id=35538 (possible miscompile for -0.0)
D61802 (should be able to reduce with IR-level FMF)

Differential Revision: https://reviews.llvm.org/D62272

llvm-svn: 362612

1 files changed, 9 insertions, 3 deletions

diff --git a/llvm/lib/Transforms/Vectorize/SLPVectorizer.cpp b/llvm/lib/Transforms/Vectorize/SLPVectorizer.cpp
index c0c2c85b8f4..72fc9cf41ef 100644
--- a/llvm/lib/Transforms/Vectorize/SLPVectorizer.cpp
+++ b/llvm/lib/Transforms/Vectorize/SLPVectorizer.cpp
@@ -6105,6 +6105,9 @@ public:
     unsigned ReduxWidth = PowerOf2Floor(NumReducedVals);
 
     Value *VectorizedTree = nullptr;
+
+    // FIXME: Fast-math-flags should be set based on the instructions in the
+    //        reduction (not all of 'fast' are required).
     IRBuilder<> Builder(cast<Instruction>(ReductionRoot));
     FastMathFlags Unsafe;
     Unsafe.setFast();
@@ -6294,11 +6297,14 @@ private:
     assert(isPowerOf2_32(ReduxWidth) &&
            "We only handle power-of-two reductions for now");
 
-    if (!IsPairwiseReduction)
+    if (!IsPairwiseReduction) {
+      // FIXME: The builder should use an FMF guard. It should not be hard-coded
+      //        to 'fast'.
+      assert(Builder.getFastMathFlags().isFast() && "Expected 'fast' FMF");
       return createSimpleTargetReduction(
           Builder, TTI, ReductionData.getOpcode(), VectorizedValue,
-          ReductionData.getFlags(), FastMathFlags::getFast(),
-          ReductionOps.back());
+          ReductionData.getFlags(), ReductionOps.back());
+    }
 
     Value *TmpVec = VectorizedValue;
     for (unsigned i = ReduxWidth / 2; i != 0; i >>= 1) {