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[ConstraintElimination] Use ZExtValue for unsigned decomposition. 

When decomposing constraints for unsigned conditions, we can use
negative values by zero-extending them, as long as they are less than
the maximum constraint value.

Fixes https://github.com/llvm/llvm-project/issues/54224
This commit is contained in:
Florian Hahn 2022-03-07 13:33:50 +00:00
parent 873e630d6c
commit 4bbee17ecb
No known key found for this signature in database
GPG Key ID: EEF712BB5E80EBBA
2 changed files with 10 additions and 9 deletions
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9
llvm/lib/Transforms/Scalar/ConstraintElimination.cpp
View File

@ -153,9 +153,9 @@ decompose(Value *V, SmallVector<PreconditionTy, 4> &Preconditions,
}
if (auto *CI = dyn_cast<ConstantInt>(V)) {
if (CI->isNegative() || CI->uge(MaxConstraintValue))
if (CI->uge(MaxConstraintValue))
return {};
return {{CI->getSExtValue(), nullptr}};
return {{CI->getZExtValue(), nullptr}};
}
auto *GEP = dyn_cast<GetElementPtrInst>(V);
if (GEP && GEP->getNumOperands() == 2 && GEP->isInBounds()) {
@ -208,8 +208,9 @@ decompose(Value *V, SmallVector<PreconditionTy, 4> &Preconditions,
Value *Op1;
ConstantInt *CI;
if (match(V, m_NUWAdd(m_Value(Op0), m_ConstantInt(CI))))
return {{CI->getSExtValue(), nullptr}, {1, Op0}};
if (match(V, m_NUWAdd(m_Value(Op0), m_ConstantInt(CI))) &&
!CI->uge(MaxConstraintValue))
return {{CI->getZExtValue(), nullptr}, {1, Op0}};
if (match(V, m_Add(m_Value(Op0), m_ConstantInt(CI))) && CI->isNegative()) {
Preconditions.emplace_back(
CmpInst::ICMP_UGE, Op0,

10
llvm/test/Transforms/ConstraintElimination/add-nuw.ll
View File

@ -463,10 +463,10 @@ define i1 @add_nuw_neg_pr54224_i16(i16 %a) {
; CHECK-NEXT: br i1 [[C_1]], label [[EXIT_1:%.*]], label [[EXIT_2:%.*]]
; CHECK: exit.1:
; CHECK-NEXT: [[C_2:%.*]] = icmp ugt i16 [[A]], 0
; CHECK-NEXT: ret i1 [[C_2]]
; CHECK-NEXT: ret i1 false
; CHECK: exit.2:
; CHECK-NEXT: [[C_3:%.*]] = icmp ugt i16 [[A]], 0
; CHECK-NEXT: ret i1 true
; CHECK-NEXT: ret i1 [[C_3]]
;
entry:
%neg2 = add nuw i16 %a, -305
@ -493,7 +493,7 @@ define i1 @add_nuw_neg_pr54224_i64(i64 %a) {
; CHECK-NEXT: ret i1 [[C_2]]
; CHECK: exit.2:
; CHECK-NEXT: [[C_3:%.*]] = icmp ugt i64 [[A]], 0
; CHECK-NEXT: ret i1 true
; CHECK-NEXT: ret i1 [[C_3]]
;
entry:
%neg2 = add nuw i64 %a, -305
@ -518,12 +518,12 @@ define i1 @add_nuw_neg2_i8(i8 %a) {
; CHECK: exit.1:
; CHECK-NEXT: [[T_1:%.*]] = icmp ult i8 [[A]], 2
; CHECK-NEXT: [[C_2:%.*]] = icmp ult i8 [[A]], 1
; CHECK-NEXT: [[RES_1:%.*]] = xor i1 [[T_1]], [[C_2]]
; CHECK-NEXT: [[RES_1:%.*]] = xor i1 true, [[C_2]]
; CHECK-NEXT: ret i1 [[RES_1]]
; CHECK: exit.2:
; CHECK-NEXT: [[C_3:%.*]] = icmp ult i8 [[A]], 3
; CHECK-NEXT: [[F_1:%.*]] = icmp ult i8 [[A]], 2
; CHECK-NEXT: [[RES_2:%.*]] = xor i1 [[C_3]], [[F_1]]
; CHECK-NEXT: [[RES_2:%.*]] = xor i1 [[C_3]], false
; CHECK-NEXT: ret i1 [[RES_2]]
;
entry: