[NFC][SimplifyCFG] Extract `IncomingValuesAreCompatible()` out of `SafeToMergeTerminators()`

1 files changed, 28 insertions, 11 deletions

diff --git a/llvm/lib/Transforms/Utils/SimplifyCFG.cpp b/llvm/lib/Transforms/Utils/SimplifyCFG.cpp
index ce528e4..d72718e 100644
--- a/llvm/lib/Transforms/Utils/SimplifyCFG.cpp
+++ b/llvm/lib/Transforms/Utils/SimplifyCFG.cpp
@@ -293,6 +293,23 @@ public:
 
 } // end anonymous namespace
 
+/// Return true if all the PHI nodes in the basic block \p BB
+/// receive compatible (identical) incoming values when coming from
+/// all of the predecessor blocks that are specified in \p IncomingBlocks.
+static bool IncomingValuesAreCompatible(BasicBlock *BB,
+                                        ArrayRef<BasicBlock *> IncomingBlocks) {
+  assert(IncomingBlocks.size() == 2 &&
+         "Only for a pair of incoming blocks at the time!");
+
+  // FIXME: it is okay if one of the incoming values is an `undef` value,
+  //        iff the other incoming value is guaranteed to be a non-poison value.
+  // FIXME: it is okay if one of the incoming values is a `poison` value.
+  return all_of(BB->phis(), [IncomingBlocks](PHINode &PN) {
+    return PN.getIncomingValueForBlock(IncomingBlocks[0]) ==
+           PN.getIncomingValueForBlock(IncomingBlocks[1]);
+  });
+}
+
 /// Return true if it is safe to merge these two
 /// terminator instructions together.
 static bool
@@ -309,17 +326,17 @@ SafeToMergeTerminators(Instruction *SI1, Instruction *SI2,
 
   SmallPtrSet<BasicBlock *, 16> SI1Succs(succ_begin(SI1BB), succ_end(SI1BB));
   bool Fail = false;
-  for (BasicBlock *Succ : successors(SI2BB))
-    if (SI1Succs.count(Succ))
-      for (BasicBlock::iterator BBI = Succ->begin(); isa<PHINode>(BBI); ++BBI) {
-        PHINode *PN = cast<PHINode>(BBI);
-        if (PN->getIncomingValueForBlock(SI1BB) !=
-            PN->getIncomingValueForBlock(SI2BB)) {
-          if (FailBlocks)
-            FailBlocks->insert(Succ);
-          Fail = true;
-        }
-      }
+  for (BasicBlock *Succ : successors(SI2BB)) {
+    if (!SI1Succs.count(Succ))
+      continue;
+    if (IncomingValuesAreCompatible(Succ, {SI1BB, SI2BB}))
+      continue;
+    Fail = true;
+    if (FailBlocks)
+      FailBlocks->insert(Succ);
+    else
+      break;
+  }
 
   return !Fail;
 }