[Attributor] Use AAValueConstantRange to infer dereferencability.

Reviewed By: jdoerfert

Differential Revision: https://reviews.llvm.org/D76208

1 files changed, 18 insertions, 5 deletions

diff --git a/llvm/lib/IR/Value.cpp b/llvm/lib/IR/Value.cpp
index 015bf20..cf54740 100644
--- a/llvm/lib/IR/Value.cpp
+++ b/llvm/lib/IR/Value.cpp
@@ -599,9 +599,9 @@ const Value *Value::stripPointerCastsAndInvariantGroups() const {
   return stripPointerCastsAndOffsets<PSK_ZeroIndicesAndInvariantGroups>(this);
 }
 
-const Value *
-Value::stripAndAccumulateConstantOffsets(const DataLayout &DL, APInt &Offset,
-                                         bool AllowNonInbounds) const {
+const Value *Value::stripAndAccumulateConstantOffsets(
+    const DataLayout &DL, APInt &Offset, bool AllowNonInbounds,
+    function_ref<bool(Value &, APInt &)> ExternalAnalysis) const {
   if (!getType()->isPtrOrPtrVectorTy())
     return this;
 
@@ -627,7 +627,7 @@ Value::stripAndAccumulateConstantOffsets(const DataLayout &DL, APInt &Offset,
       // of GEP's pointer type rather than the size of the original
       // pointer type.
       APInt GEPOffset(DL.getIndexTypeSizeInBits(V->getType()), 0);
-      if (!GEP->accumulateConstantOffset(DL, GEPOffset))
+      if (!GEP->accumulateConstantOffset(DL, GEPOffset, ExternalAnalysis))
         return V;
 
       // Stop traversal if the pointer offset wouldn't fit in the bit-width
@@ -636,7 +636,20 @@ Value::stripAndAccumulateConstantOffsets(const DataLayout &DL, APInt &Offset,
       if (GEPOffset.getMinSignedBits() > BitWidth)
         return V;
 
-      Offset += GEPOffset.sextOrTrunc(BitWidth);
+      // External Analysis can return a result higher/lower than the value
+      // represents. We need to detect overflow/underflow.
+      APInt GEPOffsetST = GEPOffset.sextOrTrunc(BitWidth);
+      if (!ExternalAnalysis) {
+        Offset += GEPOffsetST;
+      } else {
+        bool Overflow = false;
+        APInt OldOffset = Offset;
+        Offset = Offset.sadd_ov(GEPOffsetST, Overflow);
+        if (Overflow) {
+          Offset = OldOffset;
+          return V;
+        }
+      }
       V = GEP->getPointerOperand();
     } else if (Operator::getOpcode(V) == Instruction::BitCast ||
                Operator::getOpcode(V) == Instruction::AddrSpaceCast) {