Remove fake use of lexical copy

Author: meg-gupta

include/swift/SILOptimizer/Utils/CFGOptUtils.h

@@ -65,13 +65,14 @@ TermInst *changeEdgeValue(TermInst *branch, SILBasicBlock *dest, size_t idx,
 /// specified index. Asserts internally that the argument along the edge does
 /// not have uses.
 TermInst *deleteEdgeValue(TermInst *branch, SILBasicBlock *destBlock,
-                          size_t argIndex);
+                          size_t argIndex, bool cleanupDeadPhiOp = true);
 
 /// Erase the \p argIndex phi argument from \p block. Asserts that the argument
 /// is a /real/ phi argument. Removes all incoming values for the argument from
 /// predecessor terminators. Asserts internally that it only ever is given
 /// "true" phi argument.
-void erasePhiArgument(SILBasicBlock *block, unsigned argIndex);
+void erasePhiArgument(SILBasicBlock *block, unsigned argIndex,
+                      bool cleanupDeadPhiOp = true);
 
 /// Replace a branch target.
 ///

lib/SILOptimizer/Transforms/SILMem2Reg.cpp

@@ -698,23 +698,6 @@ StoreInst *StackAllocationPromoter::promoteAllocationInBlock(
                                        oldRunningVals->value);
         }
         runningVals = beginLexicalLifetimeAfterStore(asi, si);
-        // Create a use of the newly created copy in order to keep phi pruning
-        // from deleting our lifetime beginning instructions.
-        //
-        // TODO: Remove this hack, it is only necessary because erasePhiArgument
-        //       calls deleteEdgeValue which calls
-        //       deleteTriviallyDeadOperandsOfDeadArgument and deletes the copy
-        //       and borrow that we added and want not to have deleted.
-        SILBuilderWithScope::insertAfter(
-            runningVals->value.copy->getDefiningInstruction(),
-            [&](auto builder) {
-              SILLocation loc = RegularLocation::getAutoGeneratedLocation();
-              auto *useOfCopy =
-                  builder.createCopyValue(loc, runningVals->value.copy);
-              // Note that we don't call prepareToDelete useOfCopy because we
-              // specifically want this instruction to remain a use of copy.
-              instructionsToDelete.push_back(useOfCopy);
-            });
       }
       continue;
     }
@@ -1060,7 +1043,8 @@ void StackAllocationPromoter::fixBranchesAndUses(BlockSetVector &phiBlocks,
       auto *phi = cast<SILPhiArgument>(
           block->getArgument(block->getNumArguments() - 1));
       phi->replaceAllUsesWithUndef();
-      erasePhiArgument(block, block->getNumArguments() - 1);
+      erasePhiArgument(block, block->getNumArguments() - 1,
+                       /*cleanupDeadPhiOp*/ false);
     };
     for (auto *block : phiBlocks) {
       auto *proactivePhi = cast<SILPhiArgument>(

lib/SILOptimizer/Utils/CFGOptUtils.cpp

@@ -88,7 +88,7 @@ deleteTriviallyDeadOperandsOfDeadArgument(MutableArrayRef<Operand> termOperands,
 // Our implementation assumes that our caller is attempting to remove a dead
 // SILPhiArgument from a SILBasicBlock and has already RAUWed the argument.
 TermInst *swift::deleteEdgeValue(TermInst *branch, SILBasicBlock *destBlock,
-                                 size_t argIndex) {
+                                 size_t argIndex, bool cleanupDeadPhiOps) {
   if (auto *cbi = dyn_cast<CondBranchInst>(branch)) {
     SmallVector<SILValue, 8> trueArgs;
     SmallVector<SILValue, 8> falseArgs;
@@ -97,14 +97,18 @@ TermInst *swift::deleteEdgeValue(TermInst *branch, SILBasicBlock *destBlock,
     llvm::copy(cbi->getFalseArgs(), std::back_inserter(falseArgs));
 
     if (destBlock == cbi->getTrueBB()) {
-      deleteTriviallyDeadOperandsOfDeadArgument(cbi->getTrueOperands(),
-                                                argIndex);
+      if (cleanupDeadPhiOps) {
+        deleteTriviallyDeadOperandsOfDeadArgument(cbi->getTrueOperands(),
+                                                  argIndex);
+      }
       trueArgs.erase(trueArgs.begin() + argIndex);
     }
 
     if (destBlock == cbi->getFalseBB()) {
-      deleteTriviallyDeadOperandsOfDeadArgument(cbi->getFalseOperands(),
-                                                argIndex);
+      if (cleanupDeadPhiOps) {
+        deleteTriviallyDeadOperandsOfDeadArgument(cbi->getFalseOperands(),
+                                                  argIndex);
+      }
       falseArgs.erase(falseArgs.begin() + argIndex);
     }
 
@@ -120,8 +124,9 @@ TermInst *swift::deleteEdgeValue(TermInst *branch, SILBasicBlock *destBlock,
   if (auto *bi = dyn_cast<BranchInst>(branch)) {
     SmallVector<SILValue, 8> args;
     llvm::copy(bi->getArgs(), std::back_inserter(args));
-
-    deleteTriviallyDeadOperandsOfDeadArgument(bi->getAllOperands(), argIndex);
+    if (cleanupDeadPhiOps) {
+      deleteTriviallyDeadOperandsOfDeadArgument(bi->getAllOperands(), argIndex);
+    }
     args.erase(args.begin() + argIndex);
     auto *result = SILBuilderWithScope(bi).createBranch(bi->getLoc(),
                                                         bi->getDestBB(), args);
@@ -132,7 +137,8 @@ TermInst *swift::deleteEdgeValue(TermInst *branch, SILBasicBlock *destBlock,
   llvm_unreachable("unsupported terminator");
 }
 
-void swift::erasePhiArgument(SILBasicBlock *block, unsigned argIndex) {
+void swift::erasePhiArgument(SILBasicBlock *block, unsigned argIndex,
+                             bool cleanupDeadPhiOps) {
   assert(block->getArgument(argIndex)->isPhi()
          && "Only should be used on phi arguments");
   block->eraseArgument(argIndex);
@@ -149,7 +155,7 @@ void swift::erasePhiArgument(SILBasicBlock *block, unsigned argIndex) {
     predBlocks.insert(pred);
 
   for (auto *pred : predBlocks)
-    deleteEdgeValue(pred->getTerminator(), block, argIndex);
+    deleteEdgeValue(pred->getTerminator(), block, argIndex, cleanupDeadPhiOps);
 }
 
 /// Changes the edge value between a branch and destination basic block