[llvm] f5603aa - [ScalarEvolution] Make sure getMinusSCEV doesn't negate pointers.
Eli Friedman via llvm-commits
llvm-commits at lists.llvm.org
Wed Jul 7 10:27:50 PDT 2021
Author: Eli Friedman
Date: 2021-07-07T10:27:10-07:00
New Revision: f5603aa050cefff9052e9085920f3aa2d1d31b86
URL: https://github.com/llvm/llvm-project/commit/f5603aa050cefff9052e9085920f3aa2d1d31b86
DIFF: https://github.com/llvm/llvm-project/commit/f5603aa050cefff9052e9085920f3aa2d1d31b86.diff
LOG: [ScalarEvolution] Make sure getMinusSCEV doesn't negate pointers.
Add a function removePointerBase that returns, essentially, S -
getPointerBase(S). Use it in getMinusSCEV instead of actually
subtracting pointers.
Differential Revision: https://reviews.llvm.org/D105503
Added:
Modified:
llvm/lib/Analysis/ScalarEvolution.cpp
Removed:
################################################################################
diff --git a/llvm/lib/Analysis/ScalarEvolution.cpp b/llvm/lib/Analysis/ScalarEvolution.cpp
index 6aedd43fa46d7..843c04855bf74 100644
--- a/llvm/lib/Analysis/ScalarEvolution.cpp
+++ b/llvm/lib/Analysis/ScalarEvolution.cpp
@@ -4131,6 +4131,41 @@ const SCEV *ScalarEvolution::getNotSCEV(const SCEV *V) {
return getMinusSCEV(getMinusOne(Ty), V);
}
+/// Compute an expression equivalent to S - getPointerBase(S).
+static const SCEV *removePointerBase(ScalarEvolution *SE, const SCEV *P) {
+ assert(P->getType()->isPointerTy());
+
+ if (auto *AddRec = dyn_cast<SCEVAddRecExpr>(P)) {
+ // The base of an AddRec is the first operand.
+ SmallVector<const SCEV *> Ops{AddRec->operands()};
+ Ops[0] = removePointerBase(SE, Ops[0]);
+ // Don't try to transfer nowrap flags for now. We could in some cases
+ // (for example, if pointer operand of the AddRec is a SCEVUnknown).
+ return SE->getAddRecExpr(Ops, AddRec->getLoop(), SCEV::FlagAnyWrap);
+ }
+ if (auto *Add = dyn_cast<SCEVAddExpr>(P)) {
+ // The base of an Add is the pointer operand.
+ SmallVector<const SCEV *> Ops{Add->operands()};
+ const SCEV **PtrOp = nullptr;
+ for (const SCEV *&AddOp : Ops) {
+ if (AddOp->getType()->isPointerTy()) {
+ // If we find an Add with multiple pointer operands, treat it as a
+ // pointer base to be consistent with getPointerBase. Eventually
+ // we should be able to assert this is impossible.
+ if (PtrOp)
+ return SE->getZero(P->getType());
+ PtrOp = &AddOp;
+ }
+ }
+ *PtrOp = removePointerBase(SE, *PtrOp);
+ // Don't try to transfer nowrap flags for now. We could in some cases
+ // (for example, if the pointer operand of the Add is a SCEVUnknown).
+ return SE->getAddExpr(Ops);
+ }
+ // Any other expression must be a pointer base.
+ return SE->getZero(P->getType());
+}
+
const SCEV *ScalarEvolution::getMinusSCEV(const SCEV *LHS, const SCEV *RHS,
SCEV::NoWrapFlags Flags,
unsigned Depth) {
@@ -4145,6 +4180,8 @@ const SCEV *ScalarEvolution::getMinusSCEV(const SCEV *LHS, const SCEV *RHS,
if (!LHS->getType()->isPointerTy() ||
getPointerBase(LHS) != getPointerBase(RHS))
return getCouldNotCompute();
+ LHS = removePointerBase(this, LHS);
+ RHS = removePointerBase(this, RHS);
}
// We represent LHS - RHS as LHS + (-1)*RHS. This transformation
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