[llvm] [SCEVExpander] Preserve gep nuw during expansion (PR #102133)

[Philip Reames via llvm-commits]

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@@ -347,16 +347,19 @@ Value *SCEVExpander::InsertBinop(Instruction::BinaryOps Opcode,
 /// loop-invariant portions of expressions, after considering what
 /// can be folded using target addressing modes.
 ///
-Value *SCEVExpander::expandAddToGEP(const SCEV *Offset, Value *V) {
+Value *SCEVExpander::expandAddToGEP(const SCEV *Offset, Value *V,
+                                    SCEV::NoWrapFlags Flags) {
   assert(!isa<Instruction>(V) ||
          SE.DT.dominates(cast<Instruction>(V), &*Builder.GetInsertPoint()));
 
   Value *Idx = expand(Offset);
+  GEPNoWrapFlags NW = (Flags & SCEV::FlagNUW) ? GEPNoWrapFlags::noUnsignedWrap()
+                                              : GEPNoWrapFlags::none();
 
   // Fold a GEP with constant operands.
   if (Constant *CLHS = dyn_cast<Constant>(V))
     if (Constant *CRHS = dyn_cast<Constant>(Idx))
-      return Builder.CreatePtrAdd(CLHS, CRHS);
+      return Builder.CreatePtrAdd(CLHS, CRHS, "", NW);
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preames wrote:

Don't we need to merge the flags if we find an existing GEP in the loop below?  In particular, is it safe to reuse a GEP with flags when expanding one without?

https://github.com/llvm/llvm-project/pull/102133