[LoopVectorize] Fix assertion failure in Fcmp vectorization

Summary:
When vectorizing fcmps we can trip on incorrect cast assertion when setting the
FastMathFlags after generating the vectorized FCmp.
This can happen if the FCmp can be folded to true or false directly. The fix
here is to set the FastMathFlag using the FastMathFlagBuilder *before* creating
the FCmp Instruction. This is what's done by other optimizations such as
InstCombine.
Added a test case which trips on cast assertion without this patch.

Reviewers: Ayal, mssimpso, mkuper, gilr

Reviewed by: Ayal, mssimpso

Subscribers: llvm-commits, mzolotukhin

Differential Revision: https://reviews.llvm.org/D36244

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@310389 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/lib/Transforms/Vectorize/LoopVectorize.cpp b/lib/Transforms/Vectorize/LoopVectorize.cpp
index dbd54c49669925a3c9c05130d4e4303e0f851011..5c640542e9a9567c3cccaf563b40111efeacc39a 100644 (file)
--- a/lib/Transforms/Vectorize/LoopVectorize.cpp
+++ b/lib/Transforms/Vectorize/LoopVectorize.cpp
@@ -4863,8 +4863,10 @@ void InnerLoopVectorizer::vectorizeInstruction(Instruction &I) {
       Value *B = getOrCreateVectorValue(Cmp->getOperand(1), Part);
       Value *C = nullptr;
       if (FCmp) {
+        // Propagate fast math flags.
+        IRBuilder<>::FastMathFlagGuard FMFG(Builder);
+        Builder.setFastMathFlags(Cmp->getFastMathFlags());
         C = Builder.CreateFCmp(Cmp->getPredicate(), A, B);
-        cast<FCmpInst>(C)->copyFastMathFlags(Cmp);
       } else {
         C = Builder.CreateICmp(Cmp->getPredicate(), A, B);
       }

diff --git a/test/Transforms/LoopVectorize/fcmp-vectorize.ll b/test/Transforms/LoopVectorize/fcmp-vectorize.ll
new file mode 100644 (file)
index 0000000..ae7ce70
--- /dev/null
+++ b/test/Transforms/LoopVectorize/fcmp-vectorize.ll
@@ -0,0 +1,25 @@
+; RUN: opt -loop-vectorize -force-vector-width=4 -force-vector-interleave=1 -S %s | FileCheck %s
+
+; Avoid crashing while trying to vectorize fcmp that can be folded to vector of
+; i1 true.
+define void @test1() {
+; CHECK-LABEL: test1(
+; CHECK-LABEL: vector.body:
+; CHECK-NEXT:    %index = phi i32 [ 0, %vector.ph ], [ %index.next, %vector.body ]
+; CHECK-NEXT:    %broadcast.splatinsert = insertelement <4 x i32> undef, i32 %index, i32 0
+; CHECK:         %induction = add <4 x i32> %broadcast.splat, <i32 0, i32 1, i32 2, i32 3>
+; CHECK:         %index.next = add i32 %index, 4
+
+entry:
+  br label %loop
+
+loop:                                              ; preds = %loop, %entry
+  %iv = phi i32 [ 0, %entry ], [ %ivnext, %loop ]
+  %fcmp = fcmp uno float 0.000000e+00, 0.000000e+00
+  %ivnext = add nsw i32 %iv, 1
+  %cnd = icmp sgt i32 %iv, 142
+  br i1 %cnd, label %exit, label %loop
+
+exit:                                              ; preds = %loop
+  ret void
+}