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

[Nikita Popov via llvm-commits]

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@@ -372,8 +372,8 @@ define ptr @trunk_explicit(ptr %ptr, i64 %idx) {
 ; CHECK-LABEL: define ptr @trunk_explicit(
 ; CHECK-SAME: ptr [[PTR:%.*]], i64 [[IDX:%.*]]) {
 ; CHECK-NEXT:  entry:
-; CHECK-NEXT:    [[TMP0:%.*]] = getelementptr [[STRUCT0:%.*]], ptr [[PTR]], i64 0, i32 3, i64 [[IDX]], i32 1
-; CHECK-NEXT:    [[PTR21:%.*]] = getelementptr i8, ptr [[TMP0]], i64 3216
+; CHECK-NEXT:    [[TMP0:%.*]] = getelementptr inbounds [[STRUCT0:%.*]], ptr [[PTR]], i64 0, i32 3, i64 [[IDX]], i32 1
+; CHECK-NEXT:    [[PTR21:%.*]] = getelementptr inbounds i8, ptr [[TMP0]], i64 3216
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nikic wrote:

This isn't right. The first index of the original GEP got reassociated into a separate GEP at the end here, which generally cannot preserve inbounds. (Imagine %idx is negative.)

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