[llvm] [PatternMatch] Do not accept undef elements in m_AllOnes() and friends (PR #88217)
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Tue Apr 9 17:29:33 PDT 2024
llvmbot wrote:
<!--LLVM PR SUMMARY COMMENT-->
@llvm/pr-subscribers-llvm-ir
Author: Nikita Popov (nikic)
<details>
<summary>Changes</summary>
Change all the cstval_pred_ty based PatternMatch helpers (things like m_AllOnes and m_Zero) to only allow poison elements inside vector splats, not undef elements.
Historically, we used to represent non-demanded elements in vectors using undef. Nowadays, we use poison instead. As such, I believe that support for undef in vector splats is no longer useful.
At the same time, while poison splat elements are pretty much always safe to ignore, this is not generally the case for undef elements. We have existing miscompiles in our tests due to this (see the masked-merge-*.ll tests changed here) and it's easy to miss such cases in the future, now that we write tests using poison instead of undef elements.
I think overall, keeping support for undef elements no longer makes sense, and we should drop it. Once this is done consistently, I think we may also consider allowing poison in m_APInt by default, as doing that change is much less risky than doing the same with undef.
This PR is a stub for discussion -- this change has more than a hundred test failures in InstCombine alone, and I don't want to update all of them before we reach a consensus. The abs-1.ll test is a representative example of how I would update most tests: By replacing undef with poison. I don't think there is value in retaining the undef test coverage anymore at this point.
---
Full diff: https://github.com/llvm/llvm-project/pull/88217.diff
5 Files Affected:
- (modified) llvm/include/llvm/IR/PatternMatch.h (+5-5)
- (modified) llvm/test/Transforms/InstCombine/abs-1.ll (+8-8)
- (modified) llvm/test/Transforms/InstCombine/masked-merge-add.ll (+16-1)
- (modified) llvm/test/Transforms/InstCombine/masked-merge-or.ll (+16-1)
- (modified) llvm/test/Transforms/InstCombine/masked-merge-xor.ll (+16-1)
``````````diff
diff --git a/llvm/include/llvm/IR/PatternMatch.h b/llvm/include/llvm/IR/PatternMatch.h
index 92cb79d54afc29..c5ea14af63f862 100644
--- a/llvm/include/llvm/IR/PatternMatch.h
+++ b/llvm/include/llvm/IR/PatternMatch.h
@@ -345,7 +345,7 @@ template <int64_t Val> inline constantint_match<Val> m_ConstantInt() {
/// This helper class is used to match constant scalars, vector splats,
/// and fixed width vectors that satisfy a specified predicate.
-/// For fixed width vector constants, undefined elements are ignored.
+/// For fixed width vector constants, poison elements are ignored.
template <typename Predicate, typename ConstantVal>
struct cstval_pred_ty : public Predicate {
template <typename ITy> bool match(ITy *V) {
@@ -364,19 +364,19 @@ struct cstval_pred_ty : public Predicate {
// Non-splat vector constant: check each element for a match.
unsigned NumElts = FVTy->getNumElements();
assert(NumElts != 0 && "Constant vector with no elements?");
- bool HasNonUndefElements = false;
+ bool HasNonPoisonElements = false;
for (unsigned i = 0; i != NumElts; ++i) {
Constant *Elt = C->getAggregateElement(i);
if (!Elt)
return false;
- if (isa<UndefValue>(Elt))
+ if (isa<PoisonValue>(Elt))
continue;
auto *CV = dyn_cast<ConstantVal>(Elt);
if (!CV || !this->isValue(CV->getValue()))
return false;
- HasNonUndefElements = true;
+ HasNonPoisonElements = true;
}
- return HasNonUndefElements;
+ return HasNonPoisonElements;
}
}
return false;
diff --git a/llvm/test/Transforms/InstCombine/abs-1.ll b/llvm/test/Transforms/InstCombine/abs-1.ll
index 7355c560c820b2..32bd7a37053ed6 100644
--- a/llvm/test/Transforms/InstCombine/abs-1.ll
+++ b/llvm/test/Transforms/InstCombine/abs-1.ll
@@ -63,14 +63,14 @@ define <2 x i8> @abs_canonical_2(<2 x i8> %x) {
ret <2 x i8> %abs
}
-; Even if a constant has undef elements.
+; Even if a constant has poison elements.
-define <2 x i8> @abs_canonical_2_vec_undef_elts(<2 x i8> %x) {
-; CHECK-LABEL: @abs_canonical_2_vec_undef_elts(
+define <2 x i8> @abs_canonical_2_vec_poison_elts(<2 x i8> %x) {
+; CHECK-LABEL: @abs_canonical_2_vec_poison_elts(
; CHECK-NEXT: [[ABS:%.*]] = call <2 x i8> @llvm.abs.v2i8(<2 x i8> [[X:%.*]], i1 false)
; CHECK-NEXT: ret <2 x i8> [[ABS]]
;
- %cmp = icmp sgt <2 x i8> %x, <i8 undef, i8 -1>
+ %cmp = icmp sgt <2 x i8> %x, <i8 poison, i8 -1>
%neg = sub <2 x i8> zeroinitializer, %x
%abs = select <2 x i1> %cmp, <2 x i8> %x, <2 x i8> %neg
ret <2 x i8> %abs
@@ -208,15 +208,15 @@ define <2 x i8> @nabs_canonical_2(<2 x i8> %x) {
ret <2 x i8> %abs
}
-; Even if a constant has undef elements.
+; Even if a constant has poison elements.
-define <2 x i8> @nabs_canonical_2_vec_undef_elts(<2 x i8> %x) {
-; CHECK-LABEL: @nabs_canonical_2_vec_undef_elts(
+define <2 x i8> @nabs_canonical_2_vec_poison_elts(<2 x i8> %x) {
+; CHECK-LABEL: @nabs_canonical_2_vec_poison_elts(
; CHECK-NEXT: [[TMP1:%.*]] = call <2 x i8> @llvm.abs.v2i8(<2 x i8> [[X:%.*]], i1 false)
; CHECK-NEXT: [[ABS:%.*]] = sub <2 x i8> zeroinitializer, [[TMP1]]
; CHECK-NEXT: ret <2 x i8> [[ABS]]
;
- %cmp = icmp sgt <2 x i8> %x, <i8 -1, i8 undef>
+ %cmp = icmp sgt <2 x i8> %x, <i8 -1, i8 poison>
%neg = sub <2 x i8> zeroinitializer, %x
%abs = select <2 x i1> %cmp, <2 x i8> %neg, <2 x i8> %x
ret <2 x i8> %abs
diff --git a/llvm/test/Transforms/InstCombine/masked-merge-add.ll b/llvm/test/Transforms/InstCombine/masked-merge-add.ll
index f655153108a436..0484369e99d6a5 100644
--- a/llvm/test/Transforms/InstCombine/masked-merge-add.ll
+++ b/llvm/test/Transforms/InstCombine/masked-merge-add.ll
@@ -51,7 +51,7 @@ define <3 x i32> @p_vec_undef(<3 x i32> %x, <3 x i32> %y, <3 x i32> noundef %m)
; CHECK-NEXT: [[AND:%.*]] = and <3 x i32> [[X:%.*]], [[M:%.*]]
; CHECK-NEXT: [[NEG:%.*]] = xor <3 x i32> [[M]], <i32 -1, i32 undef, i32 -1>
; CHECK-NEXT: [[AND1:%.*]] = and <3 x i32> [[NEG]], [[Y:%.*]]
-; CHECK-NEXT: [[RET:%.*]] = or disjoint <3 x i32> [[AND]], [[AND1]]
+; CHECK-NEXT: [[RET:%.*]] = add <3 x i32> [[AND]], [[AND1]]
; CHECK-NEXT: ret <3 x i32> [[RET]]
;
%and = and <3 x i32> %x, %m
@@ -61,6 +61,21 @@ define <3 x i32> @p_vec_undef(<3 x i32> %x, <3 x i32> %y, <3 x i32> noundef %m)
ret <3 x i32> %ret
}
+define <3 x i32> @p_vec_poison(<3 x i32> %x, <3 x i32> %y, <3 x i32> noundef %m) {
+; CHECK-LABEL: @p_vec_poison(
+; CHECK-NEXT: [[AND:%.*]] = and <3 x i32> [[X:%.*]], [[M:%.*]]
+; CHECK-NEXT: [[NEG:%.*]] = xor <3 x i32> [[M]], <i32 -1, i32 poison, i32 -1>
+; CHECK-NEXT: [[AND1:%.*]] = and <3 x i32> [[NEG]], [[Y:%.*]]
+; CHECK-NEXT: [[RET:%.*]] = or disjoint <3 x i32> [[AND]], [[AND1]]
+; CHECK-NEXT: ret <3 x i32> [[RET]]
+;
+ %and = and <3 x i32> %x, %m
+ %neg = xor <3 x i32> %m, <i32 -1, i32 poison, i32 -1>
+ %and1 = and <3 x i32> %neg, %y
+ %ret = add <3 x i32> %and, %and1
+ ret <3 x i32> %ret
+}
+
; ============================================================================ ;
; Constant mask.
; ============================================================================ ;
diff --git a/llvm/test/Transforms/InstCombine/masked-merge-or.ll b/llvm/test/Transforms/InstCombine/masked-merge-or.ll
index b49ec07706e284..0531a532fc7e0a 100644
--- a/llvm/test/Transforms/InstCombine/masked-merge-or.ll
+++ b/llvm/test/Transforms/InstCombine/masked-merge-or.ll
@@ -51,7 +51,7 @@ define <3 x i32> @p_vec_undef(<3 x i32> %x, <3 x i32> %y, <3 x i32> noundef %m)
; CHECK-NEXT: [[AND:%.*]] = and <3 x i32> [[X:%.*]], [[M:%.*]]
; CHECK-NEXT: [[NEG:%.*]] = xor <3 x i32> [[M]], <i32 -1, i32 undef, i32 -1>
; CHECK-NEXT: [[AND1:%.*]] = and <3 x i32> [[NEG]], [[Y:%.*]]
-; CHECK-NEXT: [[RET:%.*]] = or disjoint <3 x i32> [[AND]], [[AND1]]
+; CHECK-NEXT: [[RET:%.*]] = or <3 x i32> [[AND]], [[AND1]]
; CHECK-NEXT: ret <3 x i32> [[RET]]
;
%and = and <3 x i32> %x, %m
@@ -61,6 +61,21 @@ define <3 x i32> @p_vec_undef(<3 x i32> %x, <3 x i32> %y, <3 x i32> noundef %m)
ret <3 x i32> %ret
}
+define <3 x i32> @p_vec_poison(<3 x i32> %x, <3 x i32> %y, <3 x i32> noundef %m) {
+; CHECK-LABEL: @p_vec_poison(
+; CHECK-NEXT: [[AND:%.*]] = and <3 x i32> [[X:%.*]], [[M:%.*]]
+; CHECK-NEXT: [[NEG:%.*]] = xor <3 x i32> [[M]], <i32 -1, i32 poison, i32 -1>
+; CHECK-NEXT: [[AND1:%.*]] = and <3 x i32> [[NEG]], [[Y:%.*]]
+; CHECK-NEXT: [[RET:%.*]] = or disjoint <3 x i32> [[AND]], [[AND1]]
+; CHECK-NEXT: ret <3 x i32> [[RET]]
+;
+ %and = and <3 x i32> %x, %m
+ %neg = xor <3 x i32> %m, <i32 -1, i32 poison, i32 -1>
+ %and1 = and <3 x i32> %neg, %y
+ %ret = or <3 x i32> %and, %and1
+ ret <3 x i32> %ret
+}
+
; ============================================================================ ;
; Constant mask.
; ============================================================================ ;
diff --git a/llvm/test/Transforms/InstCombine/masked-merge-xor.ll b/llvm/test/Transforms/InstCombine/masked-merge-xor.ll
index a6d201be68cee5..74cc7625aebff5 100644
--- a/llvm/test/Transforms/InstCombine/masked-merge-xor.ll
+++ b/llvm/test/Transforms/InstCombine/masked-merge-xor.ll
@@ -51,7 +51,7 @@ define <3 x i32> @p_vec_undef(<3 x i32> %x, <3 x i32> %y, <3 x i32> noundef %m)
; CHECK-NEXT: [[AND:%.*]] = and <3 x i32> [[X:%.*]], [[M:%.*]]
; CHECK-NEXT: [[NEG:%.*]] = xor <3 x i32> [[M]], <i32 -1, i32 undef, i32 -1>
; CHECK-NEXT: [[AND1:%.*]] = and <3 x i32> [[NEG]], [[Y:%.*]]
-; CHECK-NEXT: [[RET:%.*]] = or disjoint <3 x i32> [[AND]], [[AND1]]
+; CHECK-NEXT: [[RET:%.*]] = xor <3 x i32> [[AND]], [[AND1]]
; CHECK-NEXT: ret <3 x i32> [[RET]]
;
%and = and <3 x i32> %x, %m
@@ -61,6 +61,21 @@ define <3 x i32> @p_vec_undef(<3 x i32> %x, <3 x i32> %y, <3 x i32> noundef %m)
ret <3 x i32> %ret
}
+define <3 x i32> @p_vec_poison(<3 x i32> %x, <3 x i32> %y, <3 x i32> noundef %m) {
+; CHECK-LABEL: @p_vec_poison(
+; CHECK-NEXT: [[AND:%.*]] = and <3 x i32> [[X:%.*]], [[M:%.*]]
+; CHECK-NEXT: [[NEG:%.*]] = xor <3 x i32> [[M]], <i32 -1, i32 poison, i32 -1>
+; CHECK-NEXT: [[AND1:%.*]] = and <3 x i32> [[NEG]], [[Y:%.*]]
+; CHECK-NEXT: [[RET:%.*]] = or disjoint <3 x i32> [[AND]], [[AND1]]
+; CHECK-NEXT: ret <3 x i32> [[RET]]
+;
+ %and = and <3 x i32> %x, %m
+ %neg = xor <3 x i32> %m, <i32 -1, i32 poison, i32 -1>
+ %and1 = and <3 x i32> %neg, %y
+ %ret = xor <3 x i32> %and, %and1
+ ret <3 x i32> %ret
+}
+
; ============================================================================ ;
; Constant mask.
; ============================================================================ ;
``````````
</details>
https://github.com/llvm/llvm-project/pull/88217
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