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[WebAssembly] Constant fold wasm.dot #149619

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Merged
merged 7 commits into from
Aug 5, 2025
Merged

[WebAssembly] Constant fold wasm.dot #149619

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5563f46
[WebAssembly] Precommit test for constant folding dot
badumbatish Jul 18, 2025
50ca839
[WebAssembly] Constant fold dot operation
badumbatish Jul 18, 2025
3287cd6
Merge branch 'main' into wasm_fold_dot
badumbatish Jul 20, 2025
fa8c096
Addresses specs questions and added test to reflect
badumbatish Jul 22, 2025
10d7dc9
Addresses nit, added negative test case
badumbatish Jul 25, 2025
0271d8d
Address nits and performance issues
badumbatish Jul 29, 2025
67492fa
Addresses PR reviews
badumbatish Aug 5, 2025
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25 changes: 25 additions & 0 deletions llvm/lib/Analysis/ConstantFolding.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -1657,6 +1657,7 @@ bool llvm::canConstantFoldCallTo(const CallBase *Call, const Function *F) {
case Intrinsic::aarch64_sve_convert_from_svbool:
case Intrinsic::wasm_alltrue:
case Intrinsic::wasm_anytrue:
case Intrinsic::wasm_dot:
// WebAssembly float semantics are always known
case Intrinsic::wasm_trunc_signed:
case Intrinsic::wasm_trunc_unsigned:
Expand Down Expand Up @@ -3826,6 +3827,30 @@ static Constant *ConstantFoldFixedVectorCall(
}
return ConstantVector::get(Result);
}
case Intrinsic::wasm_dot: {
unsigned NumElements =
cast<FixedVectorType>(Operands[0]->getType())->getNumElements();

assert(NumElements == 8 && Result.size() == 4 &&
"wasm dot takes i16x8 and produces i32x4");
assert(Ty->isIntegerTy());
int32_t MulVector[8];

for (unsigned I = 0; I < NumElements; ++I) {
ConstantInt *Elt0 =
cast<ConstantInt>(Operands[0]->getAggregateElement(I));
ConstantInt *Elt1 =
cast<ConstantInt>(Operands[1]->getAggregateElement(I));

MulVector[I] = Elt0->getSExtValue() * Elt1->getSExtValue();
}
for (unsigned I = 0; I < Result.size(); I++) {
int32_t IAdd = MulVector[I * 2] + MulVector[I * 2 + 1];
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When building opt with ubsan this result in runtime errors when running the new dot.ll test:

../lib/Analysis/ConstantFolding.cpp:4011:39: runtime error: signed integer overflow: 1073741824 + 1073741824 cannot be represented in type 'int32_t' (aka 'int')
SUMMARY: UndefinedBehaviorSanitizer: undefined-behavior ../lib/Analysis/ConstantFolding.cpp:4011:39

PS. The line numbers in the pull request does not match the final line numbers in the commit, but line 4011 in the output above seems to match with this line.

Result[I] = ConstantInt::get(Ty, IAdd);
}

return ConstantVector::get(Result);
}
default:
break;
}
Expand Down
56 changes: 56 additions & 0 deletions llvm/test/Transforms/InstSimplify/ConstProp/WebAssembly/dot.ll
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Original file line number Diff line number Diff line change
@@ -0,0 +1,56 @@
; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --version 5

; RUN: opt -passes=instsimplify -S < %s | FileCheck %s

; Test that intrinsics wasm dot call are constant folded

target triple = "wasm32-unknown-unknown"


define <4 x i32> @dot_zero() {
; CHECK-LABEL: define <4 x i32> @dot_zero() {
; CHECK-NEXT: ret <4 x i32> zeroinitializer
;
%res = tail call <4 x i32> @llvm.wasm.dot(<8 x i16> zeroinitializer, <8 x i16> zeroinitializer)
ret <4 x i32> %res
}

; a = 1 2 3 4 5 6 7 8
; b = 1 2 3 4 5 6 7 8
; k1|k2 = a * b = 1 4 9 16 25 36 49 64
; k1 + k2 = (1+4) | (9 + 16) | (25 + 36) | (49 + 64)
; result = 5 | 25 | 61 | 113
define <4 x i32> @dot_nonzero() {
; CHECK-LABEL: define <4 x i32> @dot_nonzero() {
; CHECK-NEXT: ret <4 x i32> <i32 5, i32 25, i32 61, i32 113>
;
%res = tail call <4 x i32> @llvm.wasm.dot(<8 x i16> <i16 1, i16 2, i16 3, i16 4, i16 5, i16 6, i16 7, i16 8>, <8 x i16> <i16 1, i16 2, i16 3, i16 4, i16 5, i16 6, i16 7, i16 8>)
ret <4 x i32> %res
}

define <4 x i32> @dot_doubly_negative() {
; CHECK-LABEL: define <4 x i32> @dot_doubly_negative() {
; CHECK-NEXT: ret <4 x i32> splat (i32 2)
;
%res = tail call <4 x i32> @llvm.wasm.dot(<8 x i16> <i16 -1, i16 -1, i16 -1, i16 -1, i16 -1, i16 -1, i16 -1, i16 -1>, <8 x i16> <i16 -1, i16 -1, i16 -1, i16 -1, i16 -1, i16 -1, i16 -1, i16 -1>)
ret <4 x i32> %res
}

; Tests that i16 max signed values fit in i32
define <4 x i32> @dot_follow_modulo_spec_1() {
; CHECK-LABEL: define <4 x i32> @dot_follow_modulo_spec_1() {
; CHECK-NEXT: ret <4 x i32> <i32 2147352578, i32 0, i32 0, i32 0>
;
%res = tail call <4 x i32> @llvm.wasm.dot(<8 x i16> <i16 32767, i16 32767, i16 0, i16 0, i16 0, i16 0, i16 0, i16 0>, <8 x i16> <i16 32767, i16 32767, i16 0, i16 0, i16 0, i16 0, i16 0, i16 0>)
ret <4 x i32> %res
}

; Tests that i16 min signed values fit in i32
define <4 x i32> @dot_follow_modulo_spec_2() {
; CHECK-LABEL: define <4 x i32> @dot_follow_modulo_spec_2() {
; CHECK-NEXT: ret <4 x i32> <i32 -2147483648, i32 0, i32 0, i32 0>
;
%res = tail call <4 x i32> @llvm.wasm.dot(<8 x i16> <i16 -32768, i16 -32768, i16 0, i16 0, i16 0, i16 0, i16 0, i16 0>, <8 x i16> <i16 -32768, i16 -32768, i16 0, i16 0, i16 0, i16 0, i16 0, i16 0>)
ret <4 x i32> %res
}