[PM] Teach LoopDeletion to correctly update the LPM when loops are
deleted.
I've expanded its test coverage a bit including adding one test that
will crash clearly without this change.
llvm-svn: 292332
diff --git a/llvm/lib/Transforms/Scalar/LoopDeletion.cpp b/llvm/lib/Transforms/Scalar/LoopDeletion.cpp
index 62702dac..3089f5c 100644
--- a/llvm/lib/Transforms/Scalar/LoopDeletion.cpp
+++ b/llvm/lib/Transforms/Scalar/LoopDeletion.cpp
@@ -100,12 +100,16 @@
/// This entire process relies pretty heavily on LoopSimplify form and LCSSA in
/// order to make various safety checks work.
///
-/// \returns true if any changes are made, even if the loop is not deleted.
+/// \returns true if the loop is deleted.
+///
+/// This also sets the \p Changed output parameter to `true` if any changes
+/// were made. This may mutate the loop even if it is unable to delete it due
+/// to hoisting trivially loop invariant instructions out of the loop.
///
/// This also updates the relevant analysis information in \p DT, \p SE, and \p
/// LI.
static bool deleteLoopIfDead(Loop *L, DominatorTree &DT, ScalarEvolution &SE,
- LoopInfo &LI) {
+ LoopInfo &LI, bool &Changed) {
assert(L->isLCSSAForm(DT) && "Expected LCSSA!");
// We can only remove the loop if there is a preheader that we can
@@ -135,15 +139,14 @@
return false;
// Finally, we have to check that the loop really is dead.
- bool Changed = false;
if (!isLoopDead(L, SE, ExitingBlocks, ExitBlock, Changed, Preheader))
- return Changed;
+ return false;
// Don't remove loops for which we can't solve the trip count.
// They could be infinite, in which case we'd be changing program behavior.
const SCEV *S = SE.getMaxBackedgeTakenCount(L);
if (isa<SCEVCouldNotCompute>(S))
- return Changed;
+ return false;
// Now that we know the removal is safe, remove the loop by changing the
// branch from the preheader to go to the single exit block.
@@ -215,15 +218,21 @@
++NumDeleted;
- return Changed;
+ return true;
}
PreservedAnalyses LoopDeletionPass::run(Loop &L, LoopAnalysisManager &AM,
LoopStandardAnalysisResults &AR,
- LPMUpdater &) {
- bool Changed = deleteLoopIfDead(&L, AR.DT, AR.SE, AR.LI);
- if (!Changed)
+ LPMUpdater &Updater) {
+ bool Changed = false;
+
+ if (deleteLoopIfDead(&L, AR.DT, AR.SE, AR.LI, Changed)) {
+ assert(Changed && "Cannot delete a loop without changing something!");
+ // Need to update the LPM about this loop going away.
+ Updater.markLoopAsDeleted(L);
+ } else if (!Changed) {
return PreservedAnalyses::all();
+ }
return getLoopPassPreservedAnalyses();
}
@@ -262,5 +271,6 @@
ScalarEvolution &SE = getAnalysis<ScalarEvolutionWrapperPass>().getSE();
LoopInfo &LI = getAnalysis<LoopInfoWrapperPass>().getLoopInfo();
- return deleteLoopIfDead(L, DT, SE, LI);
+ bool Changed = false;
+ return deleteLoopIfDead(L, DT, SE, LI, Changed) || Changed;
}