SimplifyCFG add tracing

Author: atrick

lib/SILOptimizer/Transforms/SimplifyCFG.cpp

@@ -597,6 +597,8 @@ static bool tryDominatorBasedSimplifications(
         if (stripExpectIntrinsic(Op.get()) == DominatingCondition) {
           if (!EdgeValue)
             EdgeValue = createValueForEdge(UserInst, DominatingTerminator, Idx);
+          LLVM_DEBUG(llvm::dbgs() << "replace dominated operand\n  in "
+                     << *UserInst << "  with " << EdgeValue);
           Op.set(EdgeValue);
           Changed = true;
         }
@@ -1207,6 +1209,14 @@ bool SimplifyCFG::tryJumpThreading(BranchInst *BI) {
 /// result in exposing opportunities for CFG simplification.
 bool SimplifyCFG::simplifyBranchOperands(OperandValueArrayRef Operands) {
   InstModCallbacks callbacks;
+#ifndef NDEBUG
+  callbacks = callbacks.onDelete(
+    [](SILInstruction *instToKill) {
+      LLVM_DEBUG(llvm::dbgs() << "simplify and erase " << *instToKill);
+      instToKill->eraseFromParent();
+    });
+#endif
+
   for (auto O = Operands.begin(), E = Operands.end(); O != E; ++O) {
     // All of our interesting simplifications are on single-value instructions
     // for now.