[llvm] [InstCombine] Replace all dominated uses of condition with constants (PR #105510)

[via llvm-commits]

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@@ -3705,6 +3705,20 @@ Instruction *InstCombinerImpl::visitBranchInst(BranchInst &BI) {
     return nullptr;
   }
 
+  // Replace all dominated uses of the condition with true/false
+  if (BI.getSuccessor(0) != BI.getSuccessor(1)) {
+    for (auto &U : make_early_inc_range(Cond->uses())) {
+      BasicBlockEdge Edge0(BI.getParent(), BI.getSuccessor(0));
+      if (DT.dominates(Edge0, U)) {
+        replaceUse(U, ConstantInt::getTrue(Cond->getType()));
+        continue;
+      }
+      BasicBlockEdge Edge1(BI.getParent(), BI.getSuccessor(1));
+      if (DT.dominates(Edge1, U))
+        replaceUse(U, ConstantInt::getFalse(Cond->getType()));
+    }
+  }
+
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goldsteinn wrote:

Can we do the same thing with switches?

https://github.com/llvm/llvm-project/pull/105510