[PATCH] D70148: [SLP] fix miscompile on min/max reductions with extra uses (PR43948)
Sanjay Patel via Phabricator via llvm-commits
llvm-commits at lists.llvm.org
Tue Nov 12 14:50:04 PST 2019
spatel created this revision.
spatel added reviewers: ABataev, RKSimon, dtemirbulatov.
Herald added subscribers: hiraditya, mcrosier.
Herald added a project: LLVM.
I noticed that we could miscompile reductions while working on the recent 2-way enhancements.
The problem appears to be limited to cases where a min/max reduction has extra uses of the compare operand to the select.
I assume that the existing test in used-reduced-op.ll also shows a miscompile, but nobody noticed in such a large test?
https://reviews.llvm.org/D70148
Files:
llvm/lib/Transforms/Vectorize/SLPVectorizer.cpp
llvm/test/Transforms/SLPVectorizer/X86/reduction.ll
llvm/test/Transforms/SLPVectorizer/X86/used-reduced-op.ll
Index: llvm/test/Transforms/SLPVectorizer/X86/used-reduced-op.ll
===================================================================
--- llvm/test/Transforms/SLPVectorizer/X86/used-reduced-op.ll
+++ llvm/test/Transforms/SLPVectorizer/X86/used-reduced-op.ll
@@ -71,7 +71,7 @@
; CHECK-NEXT: [[NEG_1_1:%.*]] = sub nsw i32 0, [[SUB_1_1]]
; CHECK-NEXT: [[TMP46:%.*]] = select i1 [[TMP45]], i32 [[NEG_1_1]], i32 [[SUB_1_1]]
; CHECK-NEXT: [[CMP12_1_1:%.*]] = icmp slt i32 [[TMP46]], [[OP_EXTRA]]
-; CHECK-NEXT: [[NARROW:%.*]] = or i1 [[CMP12_1_1]], undef
+; CHECK-NEXT: [[NARROW:%.*]] = or i1 [[CMP12_1_1]], [[TMP44]]
; CHECK-NEXT: [[SPEC_SELECT8_1_1:%.*]] = select i1 [[CMP12_1_1]], i32 [[TMP46]], i32 [[OP_EXTRA]]
; CHECK-NEXT: [[SUB_2_1:%.*]] = sub i32 [[TMP30]], [[TMP3]]
; CHECK-NEXT: [[TMP47:%.*]] = icmp slt i32 [[SUB_2_1]], 0
Index: llvm/test/Transforms/SLPVectorizer/X86/reduction.ll
===================================================================
--- llvm/test/Transforms/SLPVectorizer/X86/reduction.ll
+++ llvm/test/Transforms/SLPVectorizer/X86/reduction.ll
@@ -68,7 +68,7 @@
ret i32 %sum.0.lcssa
}
-; FIXME: PR43948 - https://bugs.llvm.org/show_bug.cgi?id=43948
+; PR43948 - https://bugs.llvm.org/show_bug.cgi?id=43948
; The extra use of a non-vectorized element of a reduction must not be killed.
define i32 @horiz_max_multiple_uses([32 x i32]* %x, i32* %p) {
@@ -91,7 +91,7 @@
; CHECK-NEXT: [[TMP5:%.*]] = select i1 [[TMP4]], i32 [[TMP3]], i32 [[T4]]
; CHECK-NEXT: [[C012345:%.*]] = icmp sgt i32 [[TMP5]], [[T5]]
; CHECK-NEXT: [[T17:%.*]] = select i1 [[C012345]], i32 [[TMP5]], i32 [[T5]]
-; CHECK-NEXT: [[THREE_OR_FOUR:%.*]] = select i1 undef, i32 3, i32 4
+; CHECK-NEXT: [[THREE_OR_FOUR:%.*]] = select i1 [[TMP4]], i32 3, i32 4
; CHECK-NEXT: store i32 [[THREE_OR_FOUR]], i32* [[P:%.*]], align 8
; CHECK-NEXT: ret i32 [[T17]]
;
Index: llvm/lib/Transforms/Vectorize/SLPVectorizer.cpp
===================================================================
--- llvm/lib/Transforms/Vectorize/SLPVectorizer.cpp
+++ llvm/lib/Transforms/Vectorize/SLPVectorizer.cpp
@@ -6736,8 +6736,23 @@
VectorizedTree = VectReductionData.createOp(Builder, "op.extra", I);
}
}
- // Update users.
+
+ // Update users. For a min/max reduction that ends with a compare and
+ // select, we also have to RAUW for the compare instruction feeding the
+ // reduction root. That's because the compare may have extra uses besides
+ // the final select of the reduction.
+ Instruction *RdxCmp, *Cmp;
+ if (match(cast<Instruction>(ReductionRoot),
+ m_Select(m_Instruction(RdxCmp), m_Value(), m_Value())) &&
+ (RdxCmp->getOpcode() == Instruction::ICmp ||
+ RdxCmp->getOpcode() == Instruction::FCmp) &&
+ match(VectorizedTree,
+ m_Select(m_Instruction(Cmp), m_Value(), m_Value())) &&
+ Cmp->getOpcode() == RdxCmp->getOpcode()) {
+ RdxCmp->replaceAllUsesWith(Cmp);
+ }
ReductionRoot->replaceAllUsesWith(VectorizedTree);
+
// Mark all scalar reduction ops for deletion, they are replaced by the
// vector reductions.
V.eraseInstructions(IgnoreList);
-------------- next part --------------
A non-text attachment was scrubbed...
Name: D70148.228965.patch
Type: text/x-patch
Size: 3256 bytes
Desc: not available
URL: <http://lists.llvm.org/pipermail/llvm-commits/attachments/20191112/9971c633/attachment.bin>
More information about the llvm-commits
mailing list