[llvm] Mips: Mark the $gp setup copy dead when erasing the call's $gp use (PR #227216)

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llvmorg-github-actions[bot] wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-backend-mips

Author: Matt Arsenault (arsenm)

<details>
<summary>Changes</summary>

MipsOptimizePICCall drops the implicit $gp operand from a call when the
lazy binding stub for the callee has already run. The copy that set $gp
up for that call then has no reader left, but nothing flagged it, so the
MIR carried a live def until a later liveness recomputation cleaned it
up.

The pass already walks each block in order, so track the reaching
definition of $gp as it goes and mark it dead when the use is erased.

Co-Authored-By: Claude Opus 5 <noreply@<!-- -->anthropic.com>

---
Full diff: https://github.com/llvm/llvm-project/pull/227216.diff


2 Files Affected:

- (modified) llvm/lib/Target/Mips/MipsOptimizePICCall.cpp (+35-25) 
- (added) llvm/test/CodeGen/Mips/optimize-pic-call-dead-gp.ll (+78) 


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</details>


https://github.com/llvm/llvm-project/pull/227216