[llvm] [WIP][InstCombine] Add assume-based optimizations for equality and AMDGPU ballot patterns (PR #160670)

[Sameer Sahasrabuddhe via llvm-commits]

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@@ -3540,6 +3540,79 @@ Instruction *InstCombinerImpl::visitCallInst(CallInst &CI) {
       }
     }
 
+    // Basic assume equality optimization: assume(x == c) -> replace dominated uses of x with c
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ssahasra wrote:

Ouch! I totally missed that. Now I see that `isValidAssumeForContext()` actually checks dominance to make sure that the assume applies at the use of `x`.

https://github.com/llvm/llvm-project/pull/160670