InstCombine: Make OptimizePointerDifference more aggressive.
- Ignore pointer casts.
- Also expand GEPs that aren't constantexprs when they have one use or only constant indices.
- We now compile "&foo[i] - &foo[j]" into "i - j".
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@150961 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Transforms/InstCombine/InstCombineAddSub.cpp b/lib/Transforms/InstCombine/InstCombineAddSub.cpp
index f2be01b..908038b 100644
--- a/lib/Transforms/InstCombine/InstCombineAddSub.cpp
+++ b/lib/Transforms/InstCombine/InstCombineAddSub.cpp
@@ -479,57 +479,57 @@
// If LHS is a gep based on RHS or RHS is a gep based on LHS, we can optimize
// this.
bool Swapped = false;
- GetElementPtrInst *GEP = 0;
- ConstantExpr *CstGEP = 0;
-
- // TODO: Could also optimize &A[i] - &A[j] -> "i-j", and "&A.foo[i] - &A.foo".
+ GEPOperator *GEP1 = 0, *GEP2 = 0;
+
// For now we require one side to be the base pointer "A" or a constant
- // expression derived from it.
- if (GetElementPtrInst *LHSGEP = dyn_cast<GetElementPtrInst>(LHS)) {
+ // GEP derived from it.
+ if (GEPOperator *LHSGEP = dyn_cast<GEPOperator>(LHS)) {
// (gep X, ...) - X
if (LHSGEP->getOperand(0) == RHS) {
- GEP = LHSGEP;
+ GEP1 = LHSGEP;
Swapped = false;
- } else if (ConstantExpr *CE = dyn_cast<ConstantExpr>(RHS)) {
- // (gep X, ...) - (ce_gep X, ...)
- if (CE->getOpcode() == Instruction::GetElementPtr &&
- LHSGEP->getOperand(0) == CE->getOperand(0)) {
- CstGEP = CE;
- GEP = LHSGEP;
+ } else if (GEPOperator *RHSGEP = dyn_cast<GEPOperator>(RHS)) {
+ // (gep X, ...) - (gep X, ...)
+ if (LHSGEP->getOperand(0)->stripPointerCasts() ==
+ RHSGEP->getOperand(0)->stripPointerCasts()) {
+ GEP2 = RHSGEP;
+ GEP1 = LHSGEP;
Swapped = false;
}
}
}
- if (GetElementPtrInst *RHSGEP = dyn_cast<GetElementPtrInst>(RHS)) {
+ if (GEPOperator *RHSGEP = dyn_cast<GEPOperator>(RHS)) {
// X - (gep X, ...)
if (RHSGEP->getOperand(0) == LHS) {
- GEP = RHSGEP;
+ GEP1 = RHSGEP;
Swapped = true;
- } else if (ConstantExpr *CE = dyn_cast<ConstantExpr>(LHS)) {
- // (ce_gep X, ...) - (gep X, ...)
- if (CE->getOpcode() == Instruction::GetElementPtr &&
- RHSGEP->getOperand(0) == CE->getOperand(0)) {
- CstGEP = CE;
- GEP = RHSGEP;
+ } else if (GEPOperator *LHSGEP = dyn_cast<GEPOperator>(LHS)) {
+ // (gep X, ...) - (gep X, ...)
+ if (RHSGEP->getOperand(0)->stripPointerCasts() ==
+ LHSGEP->getOperand(0)->stripPointerCasts()) {
+ GEP2 = LHSGEP;
+ GEP1 = RHSGEP;
Swapped = true;
}
}
}
- if (GEP == 0)
+ // Avoid duplicating the arithmetic if GEP2 has non-constant indices and
+ // multiple users.
+ if (GEP1 == 0 ||
+ (GEP2 != 0 && !GEP2->hasAllConstantIndices() && !GEP2->hasOneUse()))
return 0;
// Emit the offset of the GEP and an intptr_t.
- Value *Result = EmitGEPOffset(GEP);
+ Value *Result = EmitGEPOffset(GEP1);
// If we had a constant expression GEP on the other side offsetting the
// pointer, subtract it from the offset we have.
- if (CstGEP) {
- Value *CstOffset = EmitGEPOffset(CstGEP);
- Result = Builder->CreateSub(Result, CstOffset);
+ if (GEP2) {
+ Value *Offset = EmitGEPOffset(GEP2);
+ Result = Builder->CreateSub(Result, Offset);
}
-
// If we have p - gep(p, ...) then we have to negate the result.
if (Swapped)