[llvm] [AMDGPU] Do not preserve UniformityInfo (PR #76696)

[via llvm-commits]

llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-backend-amdgpu

Author: Sameer Sahasrabuddhe (ssahasra)

<details>
<summary>Changes</summary>

UniformityInfo has a transitive dependence on CycleInfo. A transform may change the CFG in trivial ways that do not affect uniformity, but that can leave cycles in a slightly inconsistent state. In the absence of updates to CycleInfo, it's cleaner to just invalidate both analyses.

This supersedes #<!-- -->76011, which tries to recompute CycleInfo when computing UniformityInfo.

---
Full diff: https://github.com/llvm/llvm-project/pull/76696.diff


2 Files Affected:

- (modified) llvm/lib/Target/AMDGPU/AMDGPURewriteUndefForPHI.cpp (-1) 
- (modified) llvm/lib/Target/AMDGPU/AMDGPUUnifyDivergentExitNodes.cpp (-3) 


``````````diff
diff --git a/llvm/lib/Target/AMDGPU/AMDGPURewriteUndefForPHI.cpp b/llvm/lib/Target/AMDGPU/AMDGPURewriteUndefForPHI.cpp
index 459400e3359ca1..79e9312034da45 100644
--- a/llvm/lib/Target/AMDGPU/AMDGPURewriteUndefForPHI.cpp
+++ b/llvm/lib/Target/AMDGPU/AMDGPURewriteUndefForPHI.cpp
@@ -85,7 +85,6 @@ class AMDGPURewriteUndefForPHILegacy : public FunctionPass {
     AU.addRequired<DominatorTreeWrapperPass>();
 
     AU.addPreserved<DominatorTreeWrapperPass>();
-    AU.addPreserved<UniformityInfoWrapperPass>();
     AU.setPreservesCFG();
   }
 };
diff --git a/llvm/lib/Target/AMDGPU/AMDGPUUnifyDivergentExitNodes.cpp b/llvm/lib/Target/AMDGPU/AMDGPUUnifyDivergentExitNodes.cpp
index 9bc3ba161c9ebe..1bfb7c0edd80a9 100644
--- a/llvm/lib/Target/AMDGPU/AMDGPUUnifyDivergentExitNodes.cpp
+++ b/llvm/lib/Target/AMDGPU/AMDGPUUnifyDivergentExitNodes.cpp
@@ -109,9 +109,6 @@ void AMDGPUUnifyDivergentExitNodes::getAnalysisUsage(AnalysisUsage &AU) const {
     // FIXME: preserve PostDominatorTreeWrapperPass
   }
 
-  // No divergent values are changed, only blocks and branch edges.
-  AU.addPreserved<UniformityInfoWrapperPass>();
-
   // We preserve the non-critical-edgeness property
   AU.addPreservedID(BreakCriticalEdgesID);
 

``````````

</details>


https://github.com/llvm/llvm-project/pull/76696