Make LoopSimplify change conditional branches in loop exiting blocks
which branch on undef to branch on a boolean constant for the edge
exiting the loop. This helps ScalarEvolution compute trip counts for
loops.
Teach ScalarEvolution to recognize single-value PHIs, when safe, and
ForgetSymbolicName to forget such single-value PHI nodes as apprpriate
in ForgetSymbolicName.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@97126 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Analysis/ScalarEvolution.cpp b/lib/Analysis/ScalarEvolution.cpp
index 5bad4b2..fba6e20 100644
--- a/lib/Analysis/ScalarEvolution.cpp
+++ b/lib/Analysis/ScalarEvolution.cpp
@@ -2549,14 +2549,14 @@
/// the Scalars map if they reference SymName. This is used during PHI
/// resolution.
void
-ScalarEvolution::ForgetSymbolicName(Instruction *I, const SCEV *SymName) {
+ScalarEvolution::ForgetSymbolicName(Instruction *PN, const SCEV *SymName) {
SmallVector<Instruction *, 16> Worklist;
- PushDefUseChildren(I, Worklist);
+ PushDefUseChildren(PN, Worklist);
SmallPtrSet<Instruction *, 8> Visited;
- Visited.insert(I);
+ Visited.insert(PN);
while (!Worklist.empty()) {
- I = Worklist.pop_back_val();
+ Instruction *I = Worklist.pop_back_val();
if (!Visited.insert(I)) continue;
std::map<SCEVCallbackVH, const SCEV *>::iterator It =
@@ -2568,12 +2568,15 @@
continue;
// SCEVUnknown for a PHI either means that it has an unrecognized
- // structure, or it's a PHI that's in the progress of being computed
- // by createNodeForPHI. In the former case, additional loop trip
- // count information isn't going to change anything. In the later
- // case, createNodeForPHI will perform the necessary updates on its
- // own when it gets to that point.
- if (!isa<PHINode>(I) || !isa<SCEVUnknown>(It->second)) {
+ // structure, it's a PHI that's in the progress of being computed
+ // by createNodeForPHI, or it's a single-value PHI. In the first case,
+ // additional loop trip count information isn't going to change anything.
+ // In the second case, createNodeForPHI will perform the necessary
+ // updates on its own when it gets to that point. In the third, we do
+ // want to forget the SCEVUnknown.
+ if (!isa<PHINode>(I) ||
+ !isa<SCEVUnknown>(It->second) ||
+ (I != PN && It->second == SymName)) {
ValuesAtScopes.erase(It->second);
Scalars.erase(It);
}
@@ -2696,9 +2699,21 @@
return SymbolicName;
}
- // It's tempting to recognize PHIs with a unique incoming value, however
- // this leads passes like indvars to break LCSSA form. Fortunately, such
- // PHIs are rare, as instcombine zaps them.
+ // If the PHI has a single incoming value, follow that value, unless the
+ // PHI's incoming blocks are in a different loop, in which case doing so
+ // risks breaking LCSSA form. Instcombine would normally zap these, but
+ // it doesn't have DominatorTree information, so it may miss cases.
+ if (Value *V = PN->hasConstantValue(DT)) {
+ bool AllSameLoop = true;
+ Loop *PNLoop = LI->getLoopFor(PN->getParent());
+ for (size_t i = 0, e = PN->getNumIncomingValues(); i != e; ++i)
+ if (LI->getLoopFor(PN->getIncomingBlock(i)) != PNLoop) {
+ AllSameLoop = false;
+ break;
+ }
+ if (AllSameLoop)
+ return getSCEV(V);
+ }
// If it's not a loop phi, we can't handle it yet.
return getUnknown(PN);