[llvm] [ObjCARC] Allow removal of autoreleasepools (PR #85493)
John McCall via llvm-commits
llvm-commits at lists.llvm.org
Mon Mar 18 09:51:13 PDT 2024
================
@@ -756,6 +756,76 @@ void ObjCARCOpt::OptimizeAutoreleaseRVCall(Function &F,
LLVM_DEBUG(dbgs() << "New: " << *AutoreleaseRV << "\n");
}
+/// Interprocedurally determine if calls made by the given call site can
+/// possibly produce autoreleases.
+bool MayAutorelease(const CallBase &CB, unsigned Depth = 0) {
+ if (const Function *Callee = CB.getCalledFunction()) {
+ if (!Callee->hasExactDefinition())
+ return true;
+ // This recursion depth limit is big enough to cover the vast majority
+ // of cases this will ever require.
+ if (Depth > 64)
+ return true;
+ for (const BasicBlock &BB : *Callee) {
+ for (const Instruction &I : BB)
+ if (const CallBase *JCB = dyn_cast<CallBase>(&I))
+ if (!JCB->onlyReadsMemory() && MayAutorelease(*JCB, Depth + 1))
+ return true;
+ }
+ return false;
+ }
+
+ return true;
+}
+
+// Remove autorelease pools if nothing is in between then
+bool ObjCARCOpt::OptimizeAutoreleasePools(Function &F) {
+ bool didChange = false;
+ Instruction *Push = nullptr;
+ for (BasicBlock &BB : F) {
+ bool foundAnyInBlock = false;
+ for (Instruction &Inst : BB) {
+ // FIXME: For now, only support pairs that are in the same block.
+ // It is possible to do this across other blocks, but only if you can
+ // prove every single pop call site corresponds to the push via going
+ // through each successor and checking every single one, and I don't even
+ // know if the push call could be split across call sites.
+ switch (GetBasicARCInstKind(&Inst)) {
+ case ARCInstKind::AutoreleasepoolPush:
+ Push = &Inst;
+ foundAnyInBlock = true;
+ break;
+ case ARCInstKind::AutoreleasepoolPop:
+ // If this pop matches a push and nothing in between can autorelease,
+ // zap the pair.
+ if (cast<CallInst>(&Inst)->getArgOperand(0) == Push &&
+ foundAnyInBlock) {
+ Changed = true;
+ didChange = true;
+ LLVM_DEBUG(dbgs()
+ << "ObjCARCAPElim::OptimizeBB: Zapping push pop "
+ "autorelease pair:\n"
+ " Pop: "
+ << Inst << "\n"
+ << " Push: " << *Push << "\n");
+
+ Inst.eraseFromParent();
+ Push->eraseFromParent();
+ }
+ Push = nullptr;
+ break;
+ case ARCInstKind::CallOrUser:
+ if (MayAutorelease(cast<CallBase>(Inst)))
+ Push = nullptr;
----------------
rjmccall wrote:
Please only do this analysis if there's actually a `push` we're considering optimizing.
https://github.com/llvm/llvm-project/pull/85493
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