[llvm] [NFC] Remove goto in PromoteMem2Reg::RenamePass (PR #142454)

[via llvm-commits]

llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-llvm-transforms

Author: Vitaly Buka (vitalybuka)

<details>
<summary>Changes</summary>

'goto' is essentially a shortcut for push/pop for worklist.
It can be expensive if we copy vectors, but if we move them, it should
be an issue.

Without 'goto' it's easier to reason about the
code, and it `PromoteMem2Reg::RenamePass` process
exactly one edge at a time.

There is out of order processing of the first
successor, just to make this path pure NFC. I'll
remove this in follow up patch.


---
Full diff: https://github.com/llvm/llvm-project/pull/142454.diff


1 Files Affected:

- (modified) llvm/lib/Transforms/Utils/PromoteMemoryToRegister.cpp (+11-11) 


``````````diff
diff --git a/llvm/lib/Transforms/Utils/PromoteMemoryToRegister.cpp b/llvm/lib/Transforms/Utils/PromoteMemoryToRegister.cpp
index 6ba64968193cf..d84b07bd1457c 100644
--- a/llvm/lib/Transforms/Utils/PromoteMemoryToRegister.cpp
+++ b/llvm/lib/Transforms/Utils/PromoteMemoryToRegister.cpp
@@ -424,8 +424,8 @@ struct PromoteMem2Reg {
                            const SmallPtrSetImpl<BasicBlock *> &DefBlocks,
                            SmallPtrSetImpl<BasicBlock *> &LiveInBlocks);
   void RenamePass(BasicBlock *BB, BasicBlock *Pred,
-                  RenamePassData::ValVector &IncVals,
-                  RenamePassData::LocationVector &IncLocs,
+                  RenamePassData::ValVector IncVals,
+                  RenamePassData::LocationVector IncLocs,
                   std::vector<RenamePassData> &Worklist);
   bool QueuePhiNode(BasicBlock *BB, unsigned AllocaIdx, unsigned &Version);
 
@@ -869,7 +869,8 @@ void PromoteMem2Reg::run() {
     RenamePassData RPD = std::move(RenamePassWorkList.back());
     RenamePassWorkList.pop_back();
     // RenamePass may add new worklist entries.
-    RenamePass(RPD.BB, RPD.Pred, RPD.Values, RPD.Locations, RenamePassWorkList);
+    RenamePass(RPD.BB, RPD.Pred, std::move(RPD.Values),
+               std::move(RPD.Locations), RenamePassWorkList);
   } while (!RenamePassWorkList.empty());
 
   // Remove the allocas themselves from the function.
@@ -1096,10 +1097,9 @@ static void updateForIncomingValueLocation(PHINode *PN, DebugLoc DL,
 /// IncomingVals indicates what value each Alloca contains on exit from the
 /// predecessor block Pred.
 void PromoteMem2Reg::RenamePass(BasicBlock *BB, BasicBlock *Pred,
-                                RenamePassData::ValVector &IncomingVals,
-                                RenamePassData::LocationVector &IncomingLocs,
+                                RenamePassData::ValVector IncomingVals,
+                                RenamePassData::LocationVector IncomingLocs,
                                 std::vector<RenamePassData> &Worklist) {
-NextIteration:
   // If we are inserting any phi nodes into this BB, they will already be in the
   // block.
   if (PHINode *APN = dyn_cast<PHINode>(BB->begin())) {
@@ -1222,17 +1222,17 @@ void PromoteMem2Reg::RenamePass(BasicBlock *BB, BasicBlock *Pred,
   // Keep track of the successors so we don't visit the same successor twice
   SmallPtrSet<BasicBlock *, 8> VisitedSuccs;
 
-  // Handle the first successor without using the worklist.
+  // Handle the first successor after the rest, to mimic legacy behaviour.
+  // FIXME: Handle them in regular order.
   VisitedSuccs.insert(*I);
-  Pred = BB;
-  BB = *I;
   ++I;
 
   for (; I != E; ++I)
     if (VisitedSuccs.insert(*I).second)
-      Worklist.emplace_back(*I, Pred, IncomingVals, IncomingLocs);
+      Worklist.emplace_back(*I, BB, IncomingVals, IncomingLocs);
 
-  goto NextIteration;
+  Worklist.emplace_back(*succ_begin(BB), BB, std::move(IncomingVals),
+                        std::move(IncomingLocs));
 }
 
 void llvm::PromoteMemToReg(ArrayRef<AllocaInst *> Allocas, DominatorTree &DT,

``````````

</details>


https://github.com/llvm/llvm-project/pull/142454