[llvm] [SSAUpdaterBulk] Add PHI simplification pass. (PR #150936)

[Valery Pykhtin via llvm-commits]

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@@ -222,3 +222,94 @@ void SSAUpdaterBulk::RewriteAllUses(DominatorTree *DT,
     }
   }
 }
+
+// Perform a single pass of simplification over the worklist of PHIs.
+static void simplifyPass(MutableArrayRef<PHINode *> Worklist,
+                         const DataLayout &DL) {
+  for (PHINode *&PHI : Worklist) {
+    if (Value *Simplified = simplifyInstruction(PHI, DL)) {
+      PHI->replaceAllUsesWith(Simplified);
+      PHI->eraseFromParent();
+      PHI = nullptr; // Mark as removed.
+    }
+  }
+}
+
+#ifndef NDEBUG // Should this be under EXPENSIVE_CHECKS?
+// New PHI nodes should not reference one another but they may reference
+// themselves or existing PHI nodes, and existing PHI nodes may reference new
+// PHI nodes.
+static bool
+PHIAreRefEachOther(const iterator_range<BasicBlock::phi_iterator> &NewPHIs) {
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vpykhtin wrote:

Done

https://github.com/llvm/llvm-project/pull/150936