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[VPlan] Fix convertToPhisToBlends folding non poison blend to poison (#180686)

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This fixes a miscompile in #180005 where we didn't check that the first
incoming value isn't poison.

We should use the first non-poison incoming value if it exists, or just
poison if all the incoming values are poison.
This commit is contained in:
Luke Lau 2026-02-11 00:15:57 +08:00 committed by GitHub
parent d80a729572
commit f81889da29
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GPG Key ID: B5690EEEBB952194
2 changed files with 91 additions and 4 deletions
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10
llvm/lib/Transforms/Vectorize/VPlanPredicator.cpp
View File

@ -241,10 +241,12 @@ void VPPredicator::convertPhisToBlends(VPBasicBlock *VPBB) {
// be duplications since this is a simple recursive scan, but future
// optimizations will clean it up.
if (all_equal(make_filter_range(PhiR->incoming_values(), [](VPValue *V) {
return !match(V, m_Poison());
}))) {
PhiR->replaceAllUsesWith(PhiR->getIncomingValue(0));
auto NotPoison = make_filter_range(PhiR->incoming_values(), [](VPValue *V) {
return !match(V, m_Poison());
});
if (all_equal(NotPoison)) {
PhiR->replaceAllUsesWith(NotPoison.empty() ? PhiR->getIncomingValue(0)
: *NotPoison.begin());
PhiR->eraseFromParent();
continue;
}

85
llvm/test/Transforms/LoopVectorize/uniform-blend.ll
View File

@ -291,6 +291,89 @@ exit:
ret void
}
define void @blend_poison_first_argument(ptr %p, i1 %c) {
; CHECK-LABEL: define void @blend_poison_first_argument(
; CHECK-SAME: ptr [[P:%.*]], i1 [[C:%.*]]) {
; CHECK-NEXT: [[ENTRY:.*:]]
; CHECK-NEXT: br label %[[VECTOR_PH:.*]]
; CHECK: [[VECTOR_PH]]:
; CHECK-NEXT: br label %[[VECTOR_BODY:.*]]
; CHECK: [[VECTOR_BODY]]:
; CHECK-NEXT: [[INDEX:%.*]] = phi i64 [ 0, %[[VECTOR_PH]] ], [ [[INDEX_NEXT:%.*]], %[[VECTOR_BODY]] ]
; CHECK-NEXT: [[VEC_IND:%.*]] = phi <4 x i64> [ <i64 0, i64 1, i64 2, i64 3>, %[[VECTOR_PH]] ], [ [[VEC_IND_NEXT:%.*]], %[[VECTOR_BODY]] ]
; CHECK-NEXT: [[TMP0:%.*]] = getelementptr i64, ptr [[P]], i64 [[INDEX]]
; CHECK-NEXT: store <4 x i64> [[VEC_IND]], ptr [[TMP0]], align 4
; CHECK-NEXT: [[INDEX_NEXT]] = add nuw i64 [[INDEX]], 4
; CHECK-NEXT: [[VEC_IND_NEXT]] = add nuw nsw <4 x i64> [[VEC_IND]], splat (i64 4)
; CHECK-NEXT: [[TMP1:%.*]] = icmp eq i64 [[INDEX_NEXT]], 32
; CHECK-NEXT: br i1 [[TMP1]], label %[[MIDDLE_BLOCK:.*]], label %[[VECTOR_BODY]], !llvm.loop [[LOOP6:![0-9]+]]
; CHECK: [[MIDDLE_BLOCK]]:
; CHECK-NEXT: br label %[[EXIT:.*]]
; CHECK: [[EXIT]]:
; CHECK-NEXT: ret void
;
entry:
br label %loop
loop:
%iv = phi i64 [ 0, %entry ], [ %iv.next, %latch ]
br i1 %c, label %if, label %latch
if:
br label %latch
latch:
%blend = phi i64 [ %iv, %loop ], [ poison, %if ]
%gep = getelementptr i64, ptr %p, i64 %iv
store i64 %blend, ptr %gep
%iv.next = add nuw nsw i64 %iv, 1
%ec = icmp ult i64 %iv, 31
br i1 %ec, label %loop, label %exit
exit:
ret void
}
define void @blend_all_poison(ptr %p, i1 %c) {
; CHECK-LABEL: define void @blend_all_poison(
; CHECK-SAME: ptr [[P:%.*]], i1 [[C:%.*]]) {
; CHECK-NEXT: [[ENTRY:.*:]]
; CHECK-NEXT: br label %[[VECTOR_PH:.*]]
; CHECK: [[VECTOR_PH]]:
; CHECK-NEXT: br label %[[VECTOR_BODY:.*]]
; CHECK: [[VECTOR_BODY]]:
; CHECK-NEXT: [[INDEX:%.*]] = phi i64 [ 0, %[[VECTOR_PH]] ], [ [[INDEX_NEXT:%.*]], %[[VECTOR_BODY]] ]
; CHECK-NEXT: [[TMP0:%.*]] = getelementptr i64, ptr [[P]], i64 [[INDEX]]
; CHECK-NEXT: store <4 x i64> poison, ptr [[TMP0]], align 4
; CHECK-NEXT: [[INDEX_NEXT]] = add nuw i64 [[INDEX]], 4
; CHECK-NEXT: [[TMP1:%.*]] = icmp eq i64 [[INDEX_NEXT]], 32
; CHECK-NEXT: br i1 [[TMP1]], label %[[MIDDLE_BLOCK:.*]], label %[[VECTOR_BODY]], !llvm.loop [[LOOP7:![0-9]+]]
; CHECK: [[MIDDLE_BLOCK]]:
; CHECK-NEXT: br label %[[EXIT:.*]]
; CHECK: [[EXIT]]:
; CHECK-NEXT: ret void
;
entry:
br label %loop
loop:
%iv = phi i64 [ 0, %entry ], [ %iv.next, %latch ]
br i1 %c, label %if, label %latch
if:
br label %latch
latch:
%blend = phi i64 [ poison, %loop ], [ poison, %if ]
%gep = getelementptr i64, ptr %p, i64 %iv
store i64 %blend, ptr %gep
%iv.next = add nuw nsw i64 %iv, 1
%ec = icmp ult i64 %iv, 31
br i1 %ec, label %loop, label %exit
exit:
ret void
}
;.
; CHECK: [[LOOP0]] = distinct !{[[LOOP0]], [[META1:![0-9]+]], [[META2:![0-9]+]]}
@ -299,4 +382,6 @@ exit:
; CHECK: [[LOOP3]] = distinct !{[[LOOP3]], [[META1]], [[META2]]}
; CHECK: [[LOOP4]] = distinct !{[[LOOP4]], [[META1]], [[META2]]}
; CHECK: [[LOOP5]] = distinct !{[[LOOP5]], [[META1]], [[META2]]}
; CHECK: [[LOOP6]] = distinct !{[[LOOP6]], [[META1]], [[META2]]}
; CHECK: [[LOOP7]] = distinct !{[[LOOP7]], [[META1]], [[META2]]}
;.