[LoopUnrollRuntime] NFC: use the precomputed loop exit in ConnectProlog

Minor refactoring to use the preexisting loop exit that's already
calculated. We do not need to recompute the loop exit in ConnectProlog.
Apart from avoiding redundant computation, this is required for
supporting multiple loop exits when Prolog remainder loops are generated.

llvm-svn: 307417

diff --git a/llvm/lib/Transforms/Utils/LoopUnrollRuntime.cpp b/llvm/lib/Transforms/Utils/LoopUnrollRuntime.cpp
index f96c0bd..5b3282c 100644 (file)
--- a/llvm/lib/Transforms/Utils/LoopUnrollRuntime.cpp
+++ b/llvm/lib/Transforms/Utils/LoopUnrollRuntime.cpp
@@ -65,9 +65,11 @@ static cl::opt<bool> UnrollRuntimeMultiExit(
 ///   than the unroll factor.
 ///
 static void ConnectProlog(Loop *L, Value *BECount, unsigned Count,
-                          BasicBlock *PrologExit, BasicBlock *PreHeader,
-                          BasicBlock *NewPreHeader, ValueToValueMapTy &VMap,
-                          DominatorTree *DT, LoopInfo *LI, bool PreserveLCSSA) {
+                          BasicBlock *PrologExit,
+                          BasicBlock *OriginalLoopLatchExit,
+                          BasicBlock *PreHeader, BasicBlock *NewPreHeader,
+                          ValueToValueMapTy &VMap, DominatorTree *DT,
+                          LoopInfo *LI, bool PreserveLCSSA) {
   BasicBlock *Latch = L->getLoopLatch();
   assert(Latch && "Loop must have a latch");
   BasicBlock *PrologLatch = cast<BasicBlock>(VMap[Latch]);
@@ -142,17 +144,15 @@ static void ConnectProlog(Loop *L, Value *BECount, unsigned Count,
   // then (BECount + 1) cannot unsigned-overflow.
   Value *BrLoopExit =
       B.CreateICmpULT(BECount, ConstantInt::get(BECount->getType(), Count - 1));
-  BasicBlock *Exit = L->getUniqueExitBlock();
-  assert(Exit && "Loop must have a single exit block only");
   // Split the exit to maintain loop canonicalization guarantees
-  SmallVector<BasicBlock*, 4> Preds(predecessors(Exit));
-  SplitBlockPredecessors(Exit, Preds, ".unr-lcssa", DT, LI,
+  SmallVector<BasicBlock *, 4> Preds(predecessors(OriginalLoopLatchExit));
+  SplitBlockPredecessors(OriginalLoopLatchExit, Preds, ".unr-lcssa", DT, LI,
                          PreserveLCSSA);
   // Add the branch to the exit block (around the unrolled loop)
-  B.CreateCondBr(BrLoopExit, Exit, NewPreHeader);
+  B.CreateCondBr(BrLoopExit, OriginalLoopLatchExit, NewPreHeader);
   InsertPt->eraseFromParent();
   if (DT)
-    DT->changeImmediateDominator(Exit, PrologExit);
+    DT->changeImmediateDominator(OriginalLoopLatchExit, PrologExit);
 }
 
 /// Connect the unrolling epilog code to the original loop.
@@ -782,8 +782,8 @@ bool llvm::UnrollRuntimeLoopRemainder(Loop *L, unsigned Count,
   } else {
     // Connect the prolog code to the original loop and update the
     // PHI functions.
-    ConnectProlog(L, BECount, Count, PrologExit, PreHeader, NewPreHeader,
-                  VMap, DT, LI, PreserveLCSSA);
+    ConnectProlog(L, BECount, Count, PrologExit, LatchExit, PreHeader,
+                  NewPreHeader, VMap, DT, LI, PreserveLCSSA);
   }
 
   // If this loop is nested, then the loop unroller changes the code in the