Bail on unswitching a switch statement for a case with a critical edge. We name
which edge to split by pred/succ pair, which means that we can end up splitting
the wrong edge (by case value) in the switch statement entirely. Fixes PR10031!
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@132535 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Transforms/Scalar/LoopUnswitch.cpp b/lib/Transforms/Scalar/LoopUnswitch.cpp
index 01a99af..e05f29c 100644
--- a/lib/Transforms/Scalar/LoopUnswitch.cpp
+++ b/lib/Transforms/Scalar/LoopUnswitch.cpp
@@ -258,6 +258,7 @@
if (LoopCond && SI->getNumCases() > 1) {
// Find a value to unswitch on:
// FIXME: this should chose the most expensive case!
+ // FIXME: scan for a case with a non-critical edge?
Constant *UnswitchVal = SI->getCaseValue(1);
// Do not process same value again and again.
if (!UnswitchedVals.insert(UnswitchVal))
@@ -560,6 +561,8 @@
BasicBlock *ExitBlock = ExitBlocks[i];
SmallVector<BasicBlock *, 4> Preds(pred_begin(ExitBlock),
pred_end(ExitBlock));
+ // Although SplitBlockPredecessors doesn't preserve loop-simplify in
+ // general, if we call it on all predecessors of all exits then it does.
SplitBlockPredecessors(ExitBlock, Preds.data(), Preds.size(),
".us-lcssa", this);
}
@@ -915,10 +918,11 @@
// Found a dead case value. Don't remove PHI nodes in the
// successor if they become single-entry, those PHI nodes may
// be in the Users list.
-
+
BasicBlock *Switch = SI->getParent();
BasicBlock *SISucc = SI->getSuccessor(DeadCase);
BasicBlock *Latch = L->getLoopLatch();
+ if (!SI->findCaseDest(SISucc)) continue; // Edge is critical.
// If the DeadCase successor dominates the loop latch, then the
// transformation isn't safe since it will delete the sole predecessor edge
// to the latch.