Do not simplifyLatch for loops where hoisting increments couldresult in extra live range interferance

llvm-svn: 220872

3 files changed, 34 insertions, 7 deletions

diff --git a/llvm/lib/Transforms/Scalar/LoopRotation.cpp b/llvm/lib/Transforms/Scalar/LoopRotation.cpp
index ddb53926ff7..afd2eca598e 100644
--- a/llvm/lib/Transforms/Scalar/LoopRotation.cpp
+++ b/llvm/lib/Transforms/Scalar/LoopRotation.cpp
@@ -194,8 +194,13 @@ static void RewriteUsesOfClonedInstructions(BasicBlock *OrigHeader,
 /// heuristics. We handle a single arithmetic instruction along with any type
 /// conversions.
 static bool shouldSpeculateInstrs(BasicBlock::iterator Begin,
-                                  BasicBlock::iterator End) {
+                                  BasicBlock::iterator End, Loop *L) {
   bool seenIncrement = false;
+  bool MultiExitLoop = false;
+
+  if (!L->getExitingBlock())
+    MultiExitLoop = true;
+
   for (BasicBlock::iterator I = Begin; I != End; ++I) {
 
     if (!isSafeToSpeculativelyExecute(I))
@@ -219,11 +224,33 @@ static bool shouldSpeculateInstrs(BasicBlock::iterator Begin,
     case Instruction::Xor:
     case Instruction::Shl:
     case Instruction::LShr:
-    case Instruction::AShr:
+    case Instruction::AShr: {
+      Value *IVOpnd = nullptr;
+      if (isa<ConstantInt>(I->getOperand(0)))
+        IVOpnd = I->getOperand(1);
+
+      if (isa<ConstantInt>(I->getOperand(1))) {
+        if (IVOpnd)
+          return false;
+
+        IVOpnd = I->getOperand(0);
+      }
+
+      // If increment operand is used outside of the loop, this speculation
+      // could cause extra live range interference.
+      if (MultiExitLoop && IVOpnd) {
+        for (User *UseI : IVOpnd->users()) {
+          auto *UserInst = cast<Instruction>(UseI);
+          if (!L->contains(UserInst))
+            return false;
+        }
+      }
+
       if (seenIncrement)
         return false;
       seenIncrement = true;
       break;
+    }
     case Instruction::Trunc:
     case Instruction::ZExt:
     case Instruction::SExt:
@@ -259,7 +286,7 @@ bool LoopRotate::simplifyLoopLatch(Loop *L) {
   if (!BI)
     return false;
 
-  if (!shouldSpeculateInstrs(Latch->begin(), Jmp))
+  if (!shouldSpeculateInstrs(Latch->begin(), Jmp, L))
     return false;
 
   DEBUG(dbgs() << "Folding loop latch " << Latch->getName() << " into "
diff --git a/llvm/test/Transforms/LoopRotate/dbgvalue.ll b/llvm/test/Transforms/LoopRotate/dbgvalue.ll
index e90065609aa..4da0776d6c8 100644
--- a/llvm/test/Transforms/LoopRotate/dbgvalue.ll
+++ b/llvm/test/Transforms/LoopRotate/dbgvalue.ll
@@ -46,9 +46,9 @@ define void @FindFreeHorzSeg(i64 %startCol, i64 %row, i64* %rowStart) {
 ; CHECK-LABEL: define void @FindFreeHorzSeg(
 ; CHECK: %dec = add
 ; CHECK-NEXT: tail call void @llvm.dbg.value
-; CHECK-NEXT: br i1 %tobool, label %for.cond, label %[[LOOP_EXIT:[^,]*]]
-; CHECK: [[LOOP_EXIT]]:
-; CHECK-NEXT: phi i64 [ %{{[^,]*}}, %{{[^,]*}} ]
+; CHECK: %cmp = icmp
+; CHECK: br i1 %cmp
+; CHECK: phi i64 [ %{{[^,]*}}, %{{[^,]*}} ]
 ; CHECK-NEXT: br label %for.end
 
 
diff --git a/llvm/test/Transforms/LoopRotate/simplifylatch.ll b/llvm/test/Transforms/LoopRotate/simplifylatch.ll
index d646cb9d6cb..62e5b1ae11d 100644
--- a/llvm/test/Transforms/LoopRotate/simplifylatch.ll
+++ b/llvm/test/Transforms/LoopRotate/simplifylatch.ll
@@ -4,7 +4,7 @@
 @mode_table = global [4 x i32] zeroinitializer		; <[4 x i32]*> [#uses=1]
 
 ; CHECK-LABEL: @f(
-; CHECK-NOT: bb4
+; CHECK-NOT: bb:
 define i8 @f() {
 entry:
 	tail call i32 @fegetround( )		; <i32>:0 [#uses=1]