[llvm] [llvm][GVN] Propagate `trunc nuw to i1` equalities (PR #143273)

[Andreas Jonson via llvm-commits]

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@@ -2579,6 +2579,22 @@ bool GVNPass::propagateEquality(Value *LHS, Value *RHS,
 
       continue;
     }
+
+    // Propagate equality that result from truncation with no unsigned wrap
+    // like (trunc nuw i64 %v to i1) == "true" or (trunc nuw i64 %v to i1) ==
+    // "false"
+    if (auto *Trunc = dyn_cast<TruncInst>(LHS)) {
+      if (Trunc->hasNoUnsignedWrap() && Trunc->getType()->isIntegerTy(1)) {
+        Value *Input = Trunc->getOperand(0);
+        if (ConstantInt *CI = dyn_cast<ConstantInt>(RHS)) {
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andjo403 wrote:

maybe even simply do this?
```suggestion
                Worklist.emplace_back(Input,
                              ConstantInt::get(Input->getType(), IsKnownTrue));
```

https://github.com/llvm/llvm-project/pull/143273