[PATCH] D36244: [LoopVectorize] Fix assertion failure in Fcmp vectorization

[Anna Thomas via Phabricator via llvm-commits]

anna created this revision.
Herald added a subscriber: mzolotukhin.

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.


https://reviews.llvm.org/D36244

Files:
  lib/Transforms/Vectorize/LoopVectorize.cpp
  test/Transforms/LoopVectorize/fcmp-vectorize.ll


Index: test/Transforms/LoopVectorize/fcmp-vectorize.ll
===================================================================
--- /dev/null
+++ test/Transforms/LoopVectorize/fcmp-vectorize.ll
@@ -0,0 +1,29 @@
+; RUN: opt -loop-vectorize -S %s | FileCheck %s
+
+; REQUIRES: asserts
+; 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
+
+; CHECK-LABEL: loop:
+; CHECK-NEXT:    %iv = phi i32 [ %bc.resume.val, %scalar.ph ], [ %ivnext, %loop ]
+; CHECK-NEXT:    %fcmp = fcmp uno float 0.000000e+00, 0.000000e+00
+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
+}
Index: lib/Transforms/Vectorize/LoopVectorize.cpp
===================================================================
--- lib/Transforms/Vectorize/LoopVectorize.cpp
+++ lib/Transforms/Vectorize/LoopVectorize.cpp
@@ -4863,8 +4863,9 @@
       Value *B = getOrCreateVectorValue(Cmp->getOperand(1), Part);
       Value *C = nullptr;
       if (FCmp) {
+        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);
       }


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