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[ConstantFold] Fold binary arithmetic on scalable vector splats.

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It's a nice simplification, and it confuses instcombine if we don't do
it.

Differential Revision: https://reviews.llvm.org/D87422
This commit is contained in:
Eli Friedman 2020-09-09 15:22:38 -07:00
parent cfd0162bc3
commit f9df848755
2 changed files with 32 additions and 19 deletions
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35
lib/IR/ConstantFold.cpp
View File

@ -1408,12 +1408,7 @@ Constant *llvm::ConstantFoldBinaryInstruction(unsigned Opcode, Constant *C1,
return ConstantFP::get(C1->getContext(), C3V);
}
}
} else if (IsScalableVector) {
// Do not iterate on scalable vector. The number of elements is unknown at
// compile-time.
// FIXME: this branch can potentially be removed
return nullptr;
} else if (auto *VTy = dyn_cast<FixedVectorType>(C1->getType())) {
} else if (auto *VTy = dyn_cast<VectorType>(C1->getType())) {
// Fast path for splatted constants.
if (Constant *C2Splat = C2->getSplatValue()) {
if (Instruction::isIntDivRem(Opcode) && C2Splat->isNullValue())
@ -1425,22 +1420,24 @@ Constant *llvm::ConstantFoldBinaryInstruction(unsigned Opcode, Constant *C1,
}
}
// Fold each element and create a vector constant from those constants.
SmallVector<Constant*, 16> Result;
Type *Ty = IntegerType::get(VTy->getContext(), 32);
for (unsigned i = 0, e = VTy->getNumElements(); i != e; ++i) {
Constant *ExtractIdx = ConstantInt::get(Ty, i);
Constant *LHS = ConstantExpr::getExtractElement(C1, ExtractIdx);
Constant *RHS = ConstantExpr::getExtractElement(C2, ExtractIdx);
if (auto *FVTy = dyn_cast<FixedVectorType>(VTy)) {
// Fold each element and create a vector constant from those constants.
SmallVector<Constant*, 16> Result;
Type *Ty = IntegerType::get(FVTy->getContext(), 32);
for (unsigned i = 0, e = FVTy->getNumElements(); i != e; ++i) {
Constant *ExtractIdx = ConstantInt::get(Ty, i);
Constant *LHS = ConstantExpr::getExtractElement(C1, ExtractIdx);
Constant *RHS = ConstantExpr::getExtractElement(C2, ExtractIdx);
// If any element of a divisor vector is zero, the whole op is undef.
if (Instruction::isIntDivRem(Opcode) && RHS->isNullValue())
return UndefValue::get(VTy);
// If any element of a divisor vector is zero, the whole op is undef.
if (Instruction::isIntDivRem(Opcode) && RHS->isNullValue())
return UndefValue::get(VTy);
Result.push_back(ConstantExpr::get(Opcode, LHS, RHS));
Result.push_back(ConstantExpr::get(Opcode, LHS, RHS));
}
return ConstantVector::get(Result);
}
return ConstantVector::get(Result);
}
if (ConstantExpr *CE1 = dyn_cast<ConstantExpr>(C1)) {

16
test/Transforms/InstSimplify/ConstProp/vscale.ll
View File

@ -41,6 +41,14 @@ define <vscale x 4 x i32> @sub() {
ret <vscale x 4 x i32> %r
}
define <vscale x 4 x i32> @sub_splat() {
; CHECK-LABEL: @sub_splat(
; CHECK-NEXT: ret <vscale x 4 x i32> shufflevector (<vscale x 4 x i32> insertelement (<vscale x 4 x i32> undef, i32 -16, i32 0), <vscale x 4 x i32> undef, <vscale x 4 x i32> zeroinitializer)
;
%r = sub <vscale x 4 x i32> zeroinitializer, shufflevector (<vscale x 4 x i32> insertelement (<vscale x 4 x i32> undef, i32 16, i32 0), <vscale x 4 x i32> undef, <vscale x 4 x i32> zeroinitializer)
ret <vscale x 4 x i32> %r
}
define <vscale x 4 x float> @fsub() {
; CHECK-LABEL: @fsub(
; CHECK-NEXT: ret <vscale x 4 x float> undef
@ -73,6 +81,14 @@ define <vscale x 4 x i32> @udiv() {
ret <vscale x 4 x i32> %r
}
define <vscale x 4 x i32> @udiv_splat_zero() {
; CHECK-LABEL: @udiv_splat_zero(
; CHECK-NEXT: ret <vscale x 4 x i32> undef
;
%r = udiv <vscale x 4 x i32> zeroinitializer, zeroinitializer
ret <vscale x 4 x i32> %r
}
define <vscale x 4 x i32> @sdiv() {
; CHECK-LABEL: @sdiv(
; CHECK-NEXT: ret <vscale x 4 x i32> undef