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cmd/compile: preserve KeepAlive through LLVM inlining #82

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Merged
zhouguangyuan0718 merged 1 commit into from
Aug 5, 2026
Merged

cmd/compile: preserve KeepAlive through LLVM inlining #82

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16 changes: 10 additions & 6 deletions src/cmd/compile/internal/ssa/ssa2llvm.go
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Original file line number Diff line number Diff line change
Expand Up @@ -282,10 +282,14 @@ func (lfc *LLVMFuncContext) llvmLifetimeStart(slot llvmStackSlot) {
lfc.b.CreateCall(sig, fn, []llvm.Value{slot.Value}, "")
}

func (lfc *LLVMFuncContext) llvmFakeUse(value llvm.Value) {
sig := llvm.FunctionType(GlobalCtxt.VoidType(), nil, true)
fn := getOrInsertLLVMIntrinsic("llvm.fake.use", sig)
lfc.b.CreateCall(sig, fn, []llvm.Value{value}, "")
func (lfc *LLVMFuncContext) llvmKeepAlive(value llvm.Value) {
// An operand bundle is a real SSA use that follows the call through
// inlining. llvm.donothing survives long enough for the statepoint pass to
// consume that liveness, then code generation emits no instruction for it.
fn := getLLVMIntrinsicDeclaration("llvm.donothing")
bundle := llvm.NewOperandBundle("go.keepalive", []llvm.Value{value})
lfc.b.CreateCallWithOperandBundles(fn.GlobalValueType(), fn, nil, []llvm.OperandBundle{bundle}, "")
bundle.Dispose()
}

func (lfc *LLVMFuncContext) llvmUnaryIntrinsic(v *Value, name string) llvm.Value {
Expand Down Expand Up @@ -1577,12 +1581,12 @@ func (lfc *LLVMFuncContext) GenLV(v *Value) llvm.Value {
lVal = arg0()
if name, ok := v.Aux.(*ir.Name); ok {
if slot, ok := lfc.Locals[llvmLocalKeyForName(name)]; ok && slot.Type.HasPointers() {
lfc.llvmFakeUse(slot.Value)
lfc.llvmKeepAlive(slot.Value)
}
}
case OpKeepAlive:
lVal = arg1()
lfc.llvmFakeUse(arg0())
lfc.llvmKeepAlive(arg0())
case OpLocalAddr:
if v.Uses == 0 {
break
Expand Down
38 changes: 38 additions & 0 deletions src/cmd/vendor/github.com/goallc/go-llvm/ir.go
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10 changes: 10 additions & 0 deletions test/codegen/llvm_memory_order.go
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Original file line number Diff line number Diff line change
Expand Up @@ -6,8 +6,14 @@

package codegen

import "runtime"

var llvmMemoryOrderRoot *int

func llvmSemanticKeepAlive(value *int) {
runtime.KeepAlive(value)
}

//go:noinline
func llvmMemoryOrderStore(value *int) {
llvmMemoryOrderRoot = value
Expand All @@ -22,6 +28,10 @@ func llvmMemoryOrderStore(value *int) {
// LLVM-OPT: call ptr @llvm.go.gc.write.barrier(i32 2)
// LLVM-OPT: store ptr %[[VALUE]], ptr @codegen.llvmMemoryOrderRoot
// LLVM-OPT: ret ptr %[[VALUE]]
// LLVM-LABEL: define goabiinternal void @codegen.llvmSemanticKeepAlive(
// LLVM: call void @llvm.donothing() [ "go.keepalive"(ptr %{{.*}}) ]
// LLVM-OPT-LABEL: define goabiinternal void @codegen.llvmSemanticKeepAlive(
// LLVM-OPT: call void @llvm.donothing() [ "go.keepalive"(ptr %{{.*}}) ]
func llvmMemoryOrderLoad(value *int) *int {
llvmMemoryOrderStore(value)
return llvmMemoryOrderRoot
Expand Down