Teach instsimplify how to simplify comparisons of pointers which are
constant-offsets of a common base using the generic GEP-walking logic
I added for computing pointer differences in the same situation.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@153419 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Analysis/InstructionSimplify.cpp b/lib/Analysis/InstructionSimplify.cpp
index bb70d1c..16e7a72 100644
--- a/lib/Analysis/InstructionSimplify.cpp
+++ b/lib/Analysis/InstructionSimplify.cpp
@@ -1591,6 +1591,45 @@
return 0;
}
+static Constant *computePointerICmp(const TargetData &TD,
+ CmpInst::Predicate Pred,
+ Value *LHS, Value *RHS) {
+ // We can only fold certain predicates on pointer comparisons.
+ switch (Pred) {
+ default:
+ return 0;
+
+ // Equality comaprisons are easy to fold.
+ case CmpInst::ICMP_EQ:
+ case CmpInst::ICMP_NE:
+ break;
+
+ // We can only handle unsigned relational comparisons because 'inbounds' on
+ // a GEP only protects against unsigned wrapping.
+ case CmpInst::ICMP_UGT:
+ case CmpInst::ICMP_UGE:
+ case CmpInst::ICMP_ULT:
+ case CmpInst::ICMP_ULE:
+ // However, we have to switch them to their signed variants to handle
+ // negative indices from the base pointer.
+ Pred = ICmpInst::getSignedPredicate(Pred);
+ break;
+ }
+
+ Constant *LHSOffset = stripAndComputeConstantOffsets(TD, LHS);
+ if (!LHSOffset)
+ return 0;
+ Constant *RHSOffset = stripAndComputeConstantOffsets(TD, RHS);
+ if (!RHSOffset)
+ return 0;
+
+ // If LHS and RHS are not related via constant offsets to the same base
+ // value, there is nothing we can do here.
+ if (LHS != RHS)
+ return 0;
+
+ return ConstantExpr::getICmp(Pred, LHSOffset, RHSOffset);
+}
/// SimplifyICmpInst - Given operands for an ICmpInst, see if we can
/// fold the result. If not, this returns null.
@@ -2311,7 +2350,12 @@
return getFalse(ITy);
}
- // Simplify comparisons of GEPs.
+ // Simplify comparisons of related pointers using a powerful, recursive
+ // GEP-walk when we have target data available..
+ if (Q.TD && LHS->getType()->isPointerTy() && RHS->getType()->isPointerTy())
+ if (Constant *C = computePointerICmp(*Q.TD, Pred, LHS, RHS))
+ return C;
+
if (GetElementPtrInst *GLHS = dyn_cast<GetElementPtrInst>(LHS)) {
if (GEPOperator *GRHS = dyn_cast<GEPOperator>(RHS)) {
if (GLHS->getPointerOperand() == GRHS->getPointerOperand() &&