[Attributor] Liveness for internal functions.
For an internal function, if all its call sites are dead, the body of the function is considered dead.
Reviewers: jdoerfert, uenoku
Subscribers: hiraditya, llvm-commits
Differential Revision: https://reviews.llvm.org/D66155
llvm-svn: 369470
diff --git a/llvm/lib/Transforms/IPO/Attributor.cpp b/llvm/lib/Transforms/IPO/Attributor.cpp
index bbd14d7..16894d8 100644
--- a/llvm/lib/Transforms/IPO/Attributor.cpp
+++ b/llvm/lib/Transforms/IPO/Attributor.cpp
@@ -1570,13 +1570,22 @@
void initialize(Attributor &A) override {
const Function *F = getAssociatedFunction();
+
+ if (F->hasInternalLinkage())
+ return;
+
if (!F || !F->hasExactDefinition()) {
indicatePessimisticFixpoint();
return;
}
+ exploreFromEntry(A, F);
+ }
+
+ void exploreFromEntry(Attributor &A, const Function *F) {
ToBeExploredPaths.insert(&(F->getEntryBlock().front()));
AssumedLiveBlocks.insert(&(F->getEntryBlock()));
+
for (size_t i = 0; i < ToBeExploredPaths.size(); ++i)
if (const Instruction *NextNoReturnI =
findNextNoReturn(A, ToBeExploredPaths[i]))
@@ -1606,7 +1615,12 @@
"Attempted to manifest an invalid state!");
ChangeStatus HasChanged = ChangeStatus::UNCHANGED;
- const Function &F = *getAssociatedFunction();
+ Function &F = *getAssociatedFunction();
+
+ if (AssumedLiveBlocks.empty()) {
+ F.replaceAllUsesWith(UndefValue::get(F.getType()));
+ return ChangeStatus::CHANGED;
+ }
// Flag to determine if we can change an invoke to a call assuming the
// callee is nounwind. This is not possible if the personality of the
@@ -1725,6 +1739,13 @@
/// See AbstractAttribute::trackStatistics()
void trackStatistics() const override {
+ STATS_DECL(DeadInternalFunction, Function,
+ "Number of internal functions classified as dead (no live callsite)");
+ BUILD_STAT_NAME(DeadInternalFunction, Function) +=
+ (getAssociatedFunction()->hasInternalLinkage() &&
+ AssumedLiveBlocks.empty())
+ ? 1
+ : 0;
STATS_DECL(DeadBlocks, Function,
"Number of basic blocks classified as dead");
BUILD_STAT_NAME(DeadBlocks, Function) +=
@@ -1796,10 +1817,25 @@
}
ChangeStatus AAIsDeadImpl::updateImpl(Attributor &A) {
+ const Function *F = getAssociatedFunction();
+ ChangeStatus Status = ChangeStatus::UNCHANGED;
+
+ if (F->hasInternalLinkage() && AssumedLiveBlocks.empty()) {
+ auto CallSiteCheck = [&](CallSite) { return false; };
+
+ // All callsites of F are dead.
+ if (A.checkForAllCallSites(CallSiteCheck, *this, true))
+ return ChangeStatus::UNCHANGED;
+
+ // There exists at least one live call site, so we explore the function.
+ Status = ChangeStatus::CHANGED;
+
+ exploreFromEntry(A, F);
+ }
+
// Temporary collection to iterate over existing noreturn instructions. This
// will alow easier modification of NoReturnCalls collection
SmallVector<const Instruction *, 8> NoReturnChanged;
- ChangeStatus Status = ChangeStatus::UNCHANGED;
for (const Instruction *I : NoReturnCalls)
NoReturnChanged.push_back(I);
@@ -2249,6 +2285,11 @@
if (!LivenessAA)
LivenessAA =
&getAAFor<AAIsDead>(AA, IRPosition::function(*CtxI->getFunction()));
+
+ // Don't check liveness for AAIsDead.
+ if (&AA == LivenessAA)
+ return false;
+
if (!LivenessAA->isAssumedDead(CtxI))
return false;