https://github.com/ilovepi created https://github.com/llvm/llvm-project/pull/170518
In C, consecutive statements in the same scope are under CompoundStmt/CallExpr, while in C++ they typically fall under CompoundStmt/ExprWithCleanup. This leads to different behavior with respect to where pushFullExprCleanUp inserts the lifetime end markers (e.g., at the end of scope). For these cases, we can track and insert the lifetime end markers right after the call completes. Allowing the stack space to be reused immediately. This partially addresses #109204 and #43598 for improving stack usage. >From 6bd83b3470ba371f84db2ca0528a652bebe550c5 Mon Sep 17 00:00:00 2001 From: Paul Kirth <[email protected]> Date: Tue, 2 Dec 2025 15:14:32 -0800 Subject: [PATCH] [clang] Use tighter lifetime bounds for C temporary arguments In C, consecutive statements in the same scope are under CompoundStmt/CallExpr, while in C++ they typically fall under CompoundStmt/ExprWithCleanup. This leads to different behavior with respect to where pushFullExprCleanUp inserts the lifetime end markers (e.g., at the end of scope). For these cases, we can track and insert the lifetime end markers right after the call completes. Allowing the stack space to be reused immediately. This partially addresses #109204 and #43598 for improving stack usage. --- clang/lib/CodeGen/CGCall.cpp | 18 ++++++++++++++---- clang/lib/CodeGen/CGCall.h | 19 +++++++++++++++++++ clang/test/CodeGen/stack-usage-lifetimes.c | 12 ++++++------ .../CodeGenCXX/stack-reuse-miscompile.cpp | 2 +- 4 files changed, 40 insertions(+), 11 deletions(-) diff --git a/clang/lib/CodeGen/CGCall.cpp b/clang/lib/CodeGen/CGCall.cpp index 92fe954fddcff..fc827c99c22b6 100644 --- a/clang/lib/CodeGen/CGCall.cpp +++ b/clang/lib/CodeGen/CGCall.cpp @@ -4957,11 +4957,16 @@ void CodeGenFunction::EmitCallArg(CallArgList &args, const Expr *E, RawAddress ArgSlotAlloca = Address::invalid(); ArgSlot = CreateAggTemp(E->getType(), "agg.tmp", &ArgSlotAlloca); - // Emit a lifetime start/end for this temporary at the end of the full - // expression. + // Emit a lifetime start/end for this temporary. If the type has a + // destructor, then we need to keep it alive for the full expression. if (!CGM.getCodeGenOpts().NoLifetimeMarkersForTemporaries && - EmitLifetimeStart(ArgSlotAlloca.getPointer())) - pushFullExprCleanup<CallLifetimeEnd>(NormalAndEHCleanup, ArgSlotAlloca); + EmitLifetimeStart(ArgSlotAlloca.getPointer())) { + if (E->getType().isDestructedType()) { + pushFullExprCleanup<CallLifetimeEnd>(NormalAndEHCleanup, ArgSlotAlloca); + } else { + args.addLifetimeCleanup({ArgSlotAlloca.getPointer()}); + } + } } args.add(EmitAnyExpr(E, ArgSlot), type); @@ -6291,6 +6296,11 @@ RValue CodeGenFunction::EmitCall(const CGFunctionInfo &CallInfo, for (CallLifetimeEnd &LifetimeEnd : CallLifetimeEndAfterCall) LifetimeEnd.Emit(*this, /*Flags=*/{}); + if (!CGM.getCodeGenOpts().NoLifetimeMarkersForTemporaries) + for (const CallArgList::EndLifetimeInfo < : + CallArgs.getLifetimeCleanups()) + EmitLifetimeEnd(LT.Addr); + if (!ReturnValue.isExternallyDestructed() && RetTy.isDestructedType() == QualType::DK_nontrivial_c_struct) pushDestroy(QualType::DK_nontrivial_c_struct, Ret.getAggregateAddress(), diff --git a/clang/lib/CodeGen/CGCall.h b/clang/lib/CodeGen/CGCall.h index 1ef8a3f114573..aab4b64d6a4a8 100644 --- a/clang/lib/CodeGen/CGCall.h +++ b/clang/lib/CodeGen/CGCall.h @@ -299,6 +299,10 @@ class CallArgList : public SmallVector<CallArg, 8> { llvm::Instruction *IsActiveIP; }; + struct EndLifetimeInfo { + llvm::Value *Addr; + }; + void add(RValue rvalue, QualType type) { push_back(CallArg(rvalue, type)); } void addUncopiedAggregate(LValue LV, QualType type) { @@ -312,6 +316,9 @@ class CallArgList : public SmallVector<CallArg, 8> { llvm::append_range(*this, other); llvm::append_range(Writebacks, other.Writebacks); llvm::append_range(CleanupsToDeactivate, other.CleanupsToDeactivate); + LifetimeCleanups.insert(LifetimeCleanups.end(), + other.LifetimeCleanups.begin(), + other.LifetimeCleanups.end()); assert(!(StackBase && other.StackBase) && "can't merge stackbases"); if (!StackBase) StackBase = other.StackBase; @@ -352,6 +359,14 @@ class CallArgList : public SmallVector<CallArg, 8> { /// memory. bool isUsingInAlloca() const { return StackBase; } + void addLifetimeCleanup(EndLifetimeInfo Info) { + LifetimeCleanups.push_back(Info); + } + + ArrayRef<EndLifetimeInfo> getLifetimeCleanups() const { + return LifetimeCleanups; + } + // Support reversing writebacks for MSVC ABI. void reverseWritebacks() { std::reverse(Writebacks.begin(), Writebacks.end()); @@ -365,6 +380,10 @@ class CallArgList : public SmallVector<CallArg, 8> { /// occurs. SmallVector<CallArgCleanup, 1> CleanupsToDeactivate; + /// Lifetime information needed to call llvm.lifetime.end for any temporary + /// argument allocas. + SmallVector<EndLifetimeInfo, 2> LifetimeCleanups; + /// The stacksave call. It dominates all of the argument evaluation. llvm::CallInst *StackBase = nullptr; }; diff --git a/clang/test/CodeGen/stack-usage-lifetimes.c b/clang/test/CodeGen/stack-usage-lifetimes.c index 3787a29e4ce7d..189bc9c229ca4 100644 --- a/clang/test/CodeGen/stack-usage-lifetimes.c +++ b/clang/test/CodeGen/stack-usage-lifetimes.c @@ -40,11 +40,11 @@ void t1(int c) { } void t2(void) { - // x86-precise-remark@-1 {{72 stack bytes}} + // x86-precise-remark@-1 {{40 stack bytes}} // x86-sloppy-remark@-2 {{72 stack bytes}} - // aarch64-precise-remark@-3 {{80 stack bytes}} + // aarch64-precise-remark@-3 {{48 stack bytes}} // aarch64-sloppy-remark@-4 {{80 stack bytes}} - // riscv-precise-remark@-5 {{80 stack bytes}} + // riscv-precise-remark@-5 {{48 stack bytes}} // riscv-sloppy-remark@-6 {{80 stack bytes}} useA(genA()); @@ -52,11 +52,11 @@ void t2(void) { } void t3(void) { - // x86-precise-remark@-1 {{72 stack bytes}} + // x86-precise-remark@-1 {{40 stack bytes}} // x86-sloppy-remark@-2 {{72 stack bytes}} - // aarch64-precise-remark@-3 {{80 stack bytes}} + // aarch64-precise-remark@-3 {{48 stack bytes}} // aarch64-sloppy-remark@-4 {{80 stack bytes}} - // riscv-precise-remark@-5 {{80 stack bytes}} + // riscv-precise-remark@-5 {{48 stack bytes}} // riscv-sloppy-remark@-6 {{80 stack bytes}} useB(genB()); diff --git a/clang/test/CodeGenCXX/stack-reuse-miscompile.cpp b/clang/test/CodeGenCXX/stack-reuse-miscompile.cpp index 50c374d2710f4..4aef39119c94a 100644 --- a/clang/test/CodeGenCXX/stack-reuse-miscompile.cpp +++ b/clang/test/CodeGenCXX/stack-reuse-miscompile.cpp @@ -38,10 +38,10 @@ const char * f(S s) // CHECK: call void @llvm.lifetime.start.p0(ptr [[T3]]) // CHECK: call void @llvm.lifetime.start.p0(ptr [[AGG]]) // CHECK: [[T5:%.*]] = call noundef ptr @_ZN1TC1E1S(ptr {{[^,]*}} [[T3]], [2 x i32] %{{.*}}) +// CHECK: call void @llvm.lifetime.end.p0(ptr [[AGG]]) // // CHECK: call void @_ZNK1T6concatERKS_(ptr dead_on_unwind writable sret(%class.T) align 4 [[T1]], ptr {{[^,]*}} [[T2]], ptr noundef nonnull align 4 dereferenceable(16) [[T3]]) // CHECK: [[T6:%.*]] = call noundef ptr @_ZNK1T3strEv(ptr {{[^,]*}} [[T1]]) -// CHECK: call void @llvm.lifetime.end.p0(ptr [[AGG]]) // // CHECK: call void @llvm.lifetime.end.p0( // CHECK: call void @llvm.lifetime.end.p0( _______________________________________________ llvm-branch-commits mailing list [email protected] https://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-branch-commits
