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Revert "[LoopDeletion] NFC: Move phi node value setting into prepass"

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This reverts commit r306157.
It caused some timeouts in clang tests. Perhaps unreachable loops have
far too many phi nodes.
Reverting and investigating.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@306162 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Anna Thomas 2017-06-23 21:30:48 +00:00
parent 777bbb5e05
commit 48d560bf0c
1 changed files with 11 additions and 13 deletions
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24
lib/Transforms/Scalar/LoopDeletion.cpp
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@ -31,19 +31,20 @@ using namespace llvm;
STATISTIC(NumDeleted, "Number of loops deleted");
/// This function deletes dead loops. The caller of this function needs to
/// guarantee that the loop is infact dead. Here we handle two kinds of dead
/// guarantee that the loop is infact dead. Here we handle two kinds of dead
/// loop. The first kind (\p isLoopDead) is where only invariant values from
/// within the loop are used outside of it. The second kind (\p
/// isLoopNeverExecuted) is where the loop is provably never executed. We can
/// always remove never executed loops since they will not cause any difference
/// to program behaviour.
/// always remove never executed loops since they will not cause any
/// difference to program behaviour.
///
/// This also updates the relevant analysis information in \p DT, \p SE, and \p
/// LI. It also updates the loop PM if an updater struct is provided.
// TODO: This function will be used by loop-simplifyCFG as well. So, move this
// to LoopUtils.cpp
static void deleteDeadLoop(Loop *L, DominatorTree &DT, ScalarEvolution &SE,
LoopInfo &LI, LPMUpdater *Updater = nullptr);
LoopInfo &LI, bool LoopIsNeverExecuted,
LPMUpdater *Updater = nullptr);
/// Determines if a loop is dead.
///
/// This assumes that we've already checked for unique exit and exiting blocks,
@ -167,13 +168,7 @@ static bool deleteLoopIfDead(Loop *L, DominatorTree &DT, ScalarEvolution &SE,
BasicBlock *ExitBlock = L->getUniqueExitBlock();
if (ExitBlock && isLoopNeverExecuted(L)) {
// Set incoming value to undef for phi nodes in the exit block.
BasicBlock::iterator BI = ExitBlock->begin();
while (PHINode *P = dyn_cast<PHINode>(BI)) {
for (unsigned i = 0; i < P->getNumIncomingValues(); i++)
P->setIncomingValue(i, UndefValue::get(P->getType()));
}
deleteDeadLoop(L, DT, SE, LI, Updater);
deleteDeadLoop(L, DT, SE, LI, true /* LoopIsNeverExecuted */, Updater);
++NumDeleted;
return true;
}
@ -201,14 +196,15 @@ static bool deleteLoopIfDead(Loop *L, DominatorTree &DT, ScalarEvolution &SE,
if (isa<SCEVCouldNotCompute>(S))
return Changed;
deleteDeadLoop(L, DT, SE, LI, Updater);
deleteDeadLoop(L, DT, SE, LI, false /* LoopIsNeverExecuted */, Updater);
++NumDeleted;
return true;
}
static void deleteDeadLoop(Loop *L, DominatorTree &DT, ScalarEvolution &SE,
LoopInfo &LI, LPMUpdater *Updater) {
LoopInfo &LI, bool LoopIsNeverExecuted,
LPMUpdater *Updater) {
assert(L->isLCSSAForm(DT) && "Expected LCSSA!");
auto *Preheader = L->getLoopPreheader();
assert(Preheader && "Preheader should exist!");
@ -250,6 +246,8 @@ static void deleteDeadLoop(Loop *L, DominatorTree &DT, ScalarEvolution &SE,
// other incoming values. Given the loop has dedicated exits, all other
// incoming values must be from the exiting blocks.
int PredIndex = 0;
if (LoopIsNeverExecuted)
P->setIncomingValue(PredIndex, UndefValue::get(P->getType()));
P->setIncomingBlock(PredIndex, Preheader);
// Removes all incoming values from all other exiting blocks (including
// duplicate values from an exiting block).