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

[Fabian Ritter 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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ritter-x2a wrote:

The most recent commit preserves more flags based on nuw. All test cases in the updated preserve-inbounds.ll were validated by alive2 (no timeouts or memouts were hit, with `-tv-smt-to=1500000 -tv-smt-max-mem=80000 --tv-disable-undef-input`).

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