llvm-project

a6e1700f - [Utils][Local] Preserve !nosanitize in combineMetadata when merging instructions (#148376)

[Utils][Local] Preserve !nosanitize in combineMetadata when merging instructions (#148376) `combineMetadata` helper currently drops `!nosanitize` metadata when merging two instructions, even if both originally carried `!nosanitize`. This is problematic because `!nosanitize` is a key mechanism used by sanitizer (e.g., ASan) to suppress instrumentation. Removing it can lead to unintended sanitizer behavior. This patch adds `nosanitize` to the whitelist in combineMetadata, preserving it only if both instructions carry `!nosanitize`; otherwise, it is dropped. This patch also adds corresponding tests in a test file and regenerates it. --- ### Details **Example (see [Godbolt](https://godbolt.org/z/83P5eWczx) for details**): ```llvm %v1 = load i32, ptr %p, !nosanitize %v2 = load i32, ptr %p, !nosanitize ``` When merged via `combineMetadata(%v1, %v2, ...)`, the resulting instruction loses its `!nosanitize` metadata. Tools such as UBSan and AFL rely on `nosanitize` to prevent unwanted transformations or checks. However, the current implementation of combineMetadata mistakenly drops !nosanitize. This may lead to unintended behavior during optimization. For example, under `-fsanitize=address,undefined -O2`, IR emitted by UBSan may lose its `!nosanitize` metadata due to the incorrect metadata merging in optimization. As a result, ASan could unexpectedly instrument those instructions. > Note: due to the current UBSan handlers having relatively coarse-grained attributes, this specific case is difficult to reproduce end-to-end from source code—UBSan currently inhibits such optimizations (refer to #135135 for details). Still, I believe it's necessary to fix this now, to support future versions of UBSan that might allow such optimizations, and to support third-party tools (such as AFL-based fuzzers) that rely on the presence of !nosanitize.