Check for side effects before splitting loop.

Patch by Jakub Staszak!


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@102928 91177308-0d34-0410-b5e6-96231b3b80d8

lib/Transforms/Scalar/LoopIndexSplit.cpp

@@ -948,6 +948,25 @@ bool LoopIndexSplit::splitLoop() {
   if (!IVBasedValues.count(SplitCondition->getOperand(!SVOpNum)))
     return false;
 
+  // Check for side effects.
+  for (Loop::block_iterator I = L->block_begin(), E = L->block_end();
+       I != E; ++I) {
+    BasicBlock *BB = *I;
+
+    assert(DT->dominates(Header, BB));
+    if (DT->properlyDominates(SplitCondition->getParent(), BB))
+      continue;
+
+    for (BasicBlock::iterator BI = BB->begin(), BE = BB->end();
+	 BI != BE; ++BI) {
+      Instruction *Inst = BI;
+
+      if (!Inst->isSafeToSpeculativelyExecute() && !isa<PHINode>(Inst)
+	  && !isa<BranchInst>(Inst) && !isa<DbgInfoIntrinsic>(Inst))
+        return false;
+    }
+  }
+
   // Normalize loop conditions so that it is easier to calculate new loop
   // bounds.
   if (IVisGT(*ExitCondition) || IVisGE(*ExitCondition)) {

test/Transforms/LoopIndexSplit/PR4174-2.ll

@@ -0,0 +1,38 @@
+; RUN: llvm-as < %s | opt -loop-index-split | llvm-dis | not grep clone
+
+declare void @f()
+
+define fastcc i32 @main() nounwind {
+entry:
+        br label %bb1552
+
+bb1552:
+        %j295.0.reg2mem.0 = phi i32 [ %storemerge110, %bb1669 ], [ 0, %entry ]
+        br label %bb1553
+
+bb1553:
+        call void @f()
+        %tmp1628 = icmp sgt i32 %j295.0.reg2mem.0, -3
+        br i1 %tmp1628, label %bb1588, label %bb1616
+
+bb1588:
+        br label %bb1616
+
+bb1616:
+        %tmp1629 = icmp sgt i32 %j295.0.reg2mem.0, -3
+        br i1 %tmp1629, label %bb1649, label %bb1632
+
+bb1632:
+        br label %bb1669
+
+bb1649:
+        br label %bb1669
+
+bb1669:
+        %storemerge110 = add i32 %j295.0.reg2mem.0, 1
+        %tmp1672 = icmp sgt i32 %storemerge110, 3
+        br i1 %tmp1672, label %bb1678, label %bb1552
+
+bb1678:
+        ret i32 0
+}

test/Transforms/LoopIndexSplit/PR4174.ll

@@ -0,0 +1,23 @@
+; RUN: llvm-as < %s | opt -loop-index-split | llvm-dis | not grep clone
+
+declare void @f()
+
+define i32 @main() {
+entry:
+        br label %head
+head:
+        %i = phi i32 [0, %entry], [%i1, %tail]
+        call void @f()
+        %splitcond = icmp slt i32 %i, 2
+        br i1 %splitcond, label %yes, label %no
+yes:
+        br label %tail
+no:
+        br label %tail
+tail:
+        %i1 = add i32 %i, 1
+        %exitcond = icmp slt i32 %i1, 4
+        br i1 %exitcond, label %head, label %exit
+exit:
+        ret i32 0
+}