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[SLSR] handles off bounds GEPs

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Summary:
The old requirement on GEP candidates being in bounds is unnecessary.
For off-bound GEPs, we still have

  &B[i * S] = B + (i * S) * e = B + (i * e) * S

Test Plan: slsr_offbound_gep in slsr-gep.ll

Reviewers: meheff

Subscribers: llvm-commits

Differential Revision: http://reviews.llvm.org/D8809

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@233949 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Jingyue Wu 2015-04-02 21:18:32 +00:00
parent df4fd4fc4e
commit 6dedfc073a
2 changed files with 37 additions and 5 deletions
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17
lib/Transforms/Scalar/StraightLineStrengthReduce.cpp
View File

@ -333,7 +333,8 @@ void StraightLineStrengthReduce::allocateCandidateAndFindBasisForMul(
void StraightLineStrengthReduce::allocateCandidateAndFindBasisForGEP(
const SCEV *B, ConstantInt *Idx, Value *S, uint64_t ElementSize,
Instruction *I) {
// I = B + sext(Idx *nsw S) *nsw ElementSize
// I = B + sext(Idx *nsw S) * ElementSize
// = B + (sext(Idx) * sext(S)) * ElementSize
// = B + (sext(Idx) * ElementSize) * sext(S)
// Casting to IntegerType is safe because we skipped vector GEPs.
IntegerType *IntPtrTy = cast<IntegerType>(DL->getIntPtrType(I->getType()));
@ -367,7 +368,7 @@ void StraightLineStrengthReduce::factorArrayIndex(Value *ArrayIdx,
// sext'ed multiplication.
if (match(ArrayIdx, m_NSWMul(m_Value(LHS), m_ConstantInt(RHS)))) {
// SLSR is currently unsafe if i * S may overflow.
// GEP = Base + sext(LHS *nsw RHS) *nsw ElementSize
// GEP = Base + sext(LHS *nsw RHS) * ElementSize
allocateCandidateAndFindBasisForGEP(Base, RHS, LHS, ElementSize, GEP);
}
}
@ -472,19 +473,25 @@ void StraightLineStrengthReduce::rewriteCandidateWithBasis(
case Candidate::GEP:
{
Type *IntPtrTy = DL->getIntPtrType(C.Ins->getType());
bool InBounds = cast<GetElementPtrInst>(C.Ins)->isInBounds();
if (BumpWithUglyGEP) {
// C = (char *)Basis + Bump
unsigned AS = Basis.Ins->getType()->getPointerAddressSpace();
Type *CharTy = Type::getInt8PtrTy(Basis.Ins->getContext(), AS);
Reduced = Builder.CreateBitCast(Basis.Ins, CharTy);
// We only considered inbounds GEP as candidates.
Reduced = Builder.CreateInBoundsGEP(Reduced, Bump);
if (InBounds)
Reduced = Builder.CreateInBoundsGEP(Reduced, Bump);
else
Reduced = Builder.CreateGEP(Reduced, Bump);
Reduced = Builder.CreateBitCast(Reduced, C.Ins->getType());
} else {
// C = gep Basis, Bump
// Canonicalize bump to pointer size.
Bump = Builder.CreateSExtOrTrunc(Bump, IntPtrTy);
Reduced = Builder.CreateInBoundsGEP(Basis.Ins, Bump);
if (InBounds)
Reduced = Builder.CreateInBoundsGEP(Basis.Ins, Bump);
else
Reduced = Builder.CreateGEP(Basis.Ins, Bump);
}
}
break;

25
test/Transforms/StraightLineStrengthReduce/slsr-gep.ll
View File

@ -107,3 +107,28 @@ define i64 @slsr_gep_uglygep([10 x [5 x %struct.S]]* %input, i64 %s, i64 %t) {
%2 = add i64 %1, %v2
ret i64 %2
}
define i32 @slsr_out_of_bounds_gep(i32* %input, i32 %s) {
; CHECK-LABEL: @slsr_out_of_bounds_gep(
; v0 = input[0];
%p0 = getelementptr i32, i32* %input, i64 0
%v0 = load i32, i32* %p0
; v1 = input[(long)s];
%t = sext i32 %s to i64
%p1 = getelementptr i32, i32* %input, i64 %t
; CHECK: %p1 = getelementptr i32, i32* %input, i64 %t
%v1 = load i32, i32* %p1
; v2 = input[(long)(s * 2)];
%s2 = mul nsw i32 %s, 2
%t2 = sext i32 %s2 to i64
%p2 = getelementptr i32, i32* %input, i64 %t2
; CHECK: %p2 = getelementptr i32, i32* %p1, i64 %t
%v2 = load i32, i32* %p2
; return v0 + v1 + v2;
%1 = add i32 %v0, %v1
%2 = add i32 %1, %v2
ret i32 %2
}