[llvm] [SeparateConstOffsetFromGEP] Preserve inbounds flag based on ValueTracking (PR #130617)

[Nikita Popov via llvm-commits]

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@@ -1100,11 +1104,15 @@ bool SeparateConstOffsetFromGEP::splitGEP(GetElementPtrInst *GEP) {
   // address with silently-wrapping two's complement arithmetic".
   // Therefore, the final code will be a semantically equivalent.
   //
-  // TODO(jingyue): do some range analysis to keep as many inbounds as
-  // possible. GEPs with inbounds are more friendly to alias analysis.
-  // TODO(gep_nowrap): Preserve nuw at least.
-  GEPNoWrapFlags NewGEPFlags = GEPNoWrapFlags::none();
-  GEP->setNoWrapFlags(GEPNoWrapFlags::none());
+  // If the initial GEP was inbounds and all variable indices and the
+  // accumulated offsets are non-negative, they can be added in any order and
+  // the intermediate results are in bounds. So, we can preserve the inbounds
+  // flag for both GEPs. GEPs with inbounds are more friendly to alias analysis.
+  //
+  // TODO(gep_nowrap): Preserve nuw?
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nikic wrote:

FWIW, this TODO is relevant. If the GEP is inbounds nuw and the add is nuw you can preserve inbounds nuw, without additional knowledge. Don't know whether that is valuable for your use case or not.

https://github.com/llvm/llvm-project/pull/130617