/// isLoopDead - Determined if a loop is dead. This assumes that we've already
/// checked for unique exit and exiting blocks, and that the code is in LCSSA
/// form.
bool LoopDeletion::isLoopDead(Loop *L, ScalarEvolution &SE,
SmallVectorImpl<BasicBlock *> &exitingBlocks,
SmallVectorImpl<BasicBlock *> &exitBlocks,
bool &Changed, BasicBlock *Preheader) {
BasicBlock *exitBlock = exitBlocks[0];
// Make sure that all PHI entries coming from the loop are loop invariant.
// Because the code is in LCSSA form, any values used outside of the loop
// must pass through a PHI in the exit block, meaning that this check is
// sufficient to guarantee that no loop-variant values are used outside
// of the loop.
BasicBlock::iterator BI = exitBlock->begin();
bool AllEntriesInvariant = true;
bool AllOutgoingValuesSame = true;
while (PHINode *P = dyn_cast<PHINode>(BI)) {
Value *incoming = P->getIncomingValueForBlock(exitingBlocks[0]);
// Make sure all exiting blocks produce the same incoming value for the exit
// block. If there are different incoming values for different exiting
// blocks, then it is impossible to statically determine which value should
// be used.
AllOutgoingValuesSame =
all_of(makeArrayRef(exitingBlocks).slice(1), [&](BasicBlock *BB) {
return incoming == P->getIncomingValueForBlock(BB);
});
if (!AllOutgoingValuesSame)
break;
if (Instruction *I = dyn_cast<Instruction>(incoming))
if (!L->makeLoopInvariant(I, Changed, Preheader->getTerminator())) {
AllEntriesInvariant = false;
break;
}
++BI;
}
if (Changed)
SE.forgetLoopDispositions(L);
if (!AllEntriesInvariant || !AllOutgoingValuesSame)
return false;
// Make sure that no instructions in the block have potential side-effects.
// This includes instructions that could write to memory, and loads that are
// marked volatile. This could be made more aggressive by using aliasing
// information to identify readonly and readnone calls.
for (Loop::block_iterator LI = L->block_begin(), LE = L->block_end();
LI != LE; ++LI) {
for (BasicBlock::iterator BI = (*LI)->begin(), BE = (*LI)->end();
BI != BE; ++BI) {
if (BI->mayHaveSideEffects())
return false;
}
}
return true;
}
/// Determines if a loop is dead.
///
/// This assumes that we've already checked for unique exit and exiting blocks,
/// and that the code is in LCSSA form.
static bool isLoopDead(Loop *L, ScalarEvolution &SE,
SmallVectorImpl<BasicBlock *> &ExitingBlocks,
BasicBlock *ExitBlock, bool &Changed,
BasicBlock *Preheader) {
// Make sure that all PHI entries coming from the loop are loop invariant.
// Because the code is in LCSSA form, any values used outside of the loop
// must pass through a PHI in the exit block, meaning that this check is
// sufficient to guarantee that no loop-variant values are used outside
// of the loop.
BasicBlock::iterator BI = ExitBlock->begin();
bool AllEntriesInvariant = true;
bool AllOutgoingValuesSame = true;
while (PHINode *P = dyn_cast<PHINode>(BI)) {
Value *incoming = P->getIncomingValueForBlock(ExitingBlocks[0]);
// Make sure all exiting blocks produce the same incoming value for the exit
// block. If there are different incoming values for different exiting
// blocks, then it is impossible to statically determine which value should
// be used.
AllOutgoingValuesSame =
all_of(makeArrayRef(ExitingBlocks).slice(1), [&](BasicBlock *BB) {
return incoming == P->getIncomingValueForBlock(BB);
});
if (!AllOutgoingValuesSame)
break;
if (Instruction *I = dyn_cast<Instruction>(incoming))
if (!L->makeLoopInvariant(I, Changed, Preheader->getTerminator())) {
AllEntriesInvariant = false;
break;
}
++BI;
}
if (Changed)
SE.forgetLoopDispositions(L);
if (!AllEntriesInvariant || !AllOutgoingValuesSame)
return false;
// Make sure that no instructions in the block have potential side-effects.
// This includes instructions that could write to memory, and loads that are
// marked volatile.
for (auto &I : L->blocks())
if (any_of(*I, [](Instruction &I) { return I.mayHaveSideEffects(); }))
return false;
return true;
}
