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[CIR] Make use of !invariant.group metadata for const allocas #1159

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Merged
merged 1 commit into from
Dec 6, 2024
Merged

[CIR] Make use of !invariant.group metadata for const allocas #1159

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12 changes: 11 additions & 1 deletion clang/lib/CIR/Dialect/Transforms/HoistAllocas.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -48,8 +48,18 @@ static void process(cir::FuncOp func) {

mlir::Operation *insertPoint = &*entryBlock.begin();

for (auto alloca : allocas)
for (auto alloca : allocas) {
alloca->moveBefore(insertPoint);
if (alloca.getConstant()) {
// Hoisted alloca may come from the body of a loop, in which case the
// stack slot is re-used by multiple objects alive in different iterations
// of the loop. In theory, each of these objects are still constant within
// their lifetimes, but currently we're not emitting metadata to further
// describe this. So for now let's behave conservatively and remove the
// const flag on nested allocas when hoisting them.
alloca.setConstant(false);
}
}
}

void HoistAllocasPass::runOnOperation() {
Expand Down
35 changes: 27 additions & 8 deletions clang/lib/CIR/Lowering/DirectToLLVM/LowerToLLVM.cpp
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Expand Up @@ -959,8 +959,7 @@ mlir::LogicalResult CIRToLLVMVTTAddrPointOpLowering::matchAndRewrite(

if (op.getSymAddr()) {
if (op.getOffset() == 0) {
rewriter.replaceAllUsesWith(op, llvmAddr);
rewriter.eraseOp(op);
rewriter.replaceOp(op, {llvmAddr});
return mlir::success();
}

Expand Down Expand Up @@ -1490,11 +1489,21 @@ mlir::LogicalResult CIRToLLVMLoadOpLowering::matchAndRewrite(
alignment = *alignOpt;
}

// TODO: nontemporal, invariant, syncscope.
auto invariant = false;
// Under -O1 or higher optimization levels, add the invariant metadata if the
// load operation loads from a constant object.
if (lowerMod &&
lowerMod->getContext().getCodeGenOpts().OptimizationLevel > 0) {
auto addrAllocaOp =
mlir::dyn_cast_if_present<cir::AllocaOp>(op.getAddr().getDefiningOp());
invariant = addrAllocaOp && addrAllocaOp.getConstant();
}

// TODO: nontemporal, syncscope.
rewriter.replaceOpWithNewOp<mlir::LLVM::LoadOp>(
op, llvmTy, adaptor.getAddr(), /* alignment */ alignment,
op.getIsVolatile(), /* nontemporal */ false,
/* invariant */ false, /* invariantGroup */ false, ordering);
/* invariant */ false, /* invariantGroup */ invariant, ordering);
return mlir::LogicalResult::success();
}

Expand All @@ -1515,10 +1524,20 @@ mlir::LogicalResult CIRToLLVMStoreOpLowering::matchAndRewrite(
alignment = *alignOpt;
}

auto invariant = false;
// Under -O1 or higher optimization levels, add the invariant metadata if the
// store operation stores to a constant object.
if (lowerMod &&
lowerMod->getContext().getCodeGenOpts().OptimizationLevel > 0) {
auto addrAllocaOp =
mlir::dyn_cast_if_present<cir::AllocaOp>(op.getAddr().getDefiningOp());
invariant = addrAllocaOp && addrAllocaOp.getConstant();
}

// TODO: nontemporal, syncscope.
rewriter.replaceOpWithNewOp<mlir::LLVM::StoreOp>(
op, adaptor.getValue(), adaptor.getAddr(), alignment, op.getIsVolatile(),
/* nontemporal */ false, /* invariantGroup */ false, ordering);
/* nontemporal */ false, /* invariantGroup */ invariant, ordering);
return mlir::LogicalResult::success();
}

Expand Down Expand Up @@ -3887,7 +3906,9 @@ void populateCIRToLLVMConversionPatterns(
CIRToLLVMConstantOpLowering,
CIRToLLVMDerivedDataMemberOpLowering,
CIRToLLVMGetRuntimeMemberOpLowering,
CIRToLLVMGlobalOpLowering
CIRToLLVMGlobalOpLowering,
CIRToLLVMLoadOpLowering,
CIRToLLVMStoreOpLowering
// clang-format on
>(converter, patterns.getContext(), lowerModule);
patterns.add<
Expand Down Expand Up @@ -3938,7 +3959,6 @@ void populateCIRToLLVMConversionPatterns(
CIRToLLVMIsConstantOpLowering,
CIRToLLVMIsFPClassOpLowering,
CIRToLLVMLLVMIntrinsicCallOpLowering,
CIRToLLVMLoadOpLowering,
CIRToLLVMMemChrOpLowering,
CIRToLLVMMemCpyInlineOpLowering,
CIRToLLVMMemCpyOpLowering,
Expand All @@ -3958,7 +3978,6 @@ void populateCIRToLLVMConversionPatterns(
CIRToLLVMShiftOpLowering,
CIRToLLVMSignBitOpLowering,
CIRToLLVMStackSaveOpLowering,
CIRToLLVMStoreOpLowering,
CIRToLLVMSwitchFlatOpLowering,
CIRToLLVMThrowOpLowering,
CIRToLLVMTrapOpLowering,
Expand Down
14 changes: 12 additions & 2 deletions clang/lib/CIR/Lowering/DirectToLLVM/LowerToLLVM.h
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Expand Up @@ -301,8 +301,13 @@ class CIRToLLVMAllocaOpLowering
};

class CIRToLLVMLoadOpLowering : public mlir::OpConversionPattern<cir::LoadOp> {
cir::LowerModule *lowerMod;

public:
using mlir::OpConversionPattern<cir::LoadOp>::OpConversionPattern;
CIRToLLVMLoadOpLowering(const mlir::TypeConverter &typeConverter,
mlir::MLIRContext *context,
cir::LowerModule *lowerModule)
: OpConversionPattern(typeConverter, context), lowerMod(lowerModule) {}

mlir::LogicalResult
matchAndRewrite(cir::LoadOp op, OpAdaptor,
Expand All @@ -311,8 +316,13 @@ class CIRToLLVMLoadOpLowering : public mlir::OpConversionPattern<cir::LoadOp> {

class CIRToLLVMStoreOpLowering
: public mlir::OpConversionPattern<cir::StoreOp> {
cir::LowerModule *lowerMod;

public:
using mlir::OpConversionPattern<cir::StoreOp>::OpConversionPattern;
CIRToLLVMStoreOpLowering(const mlir::TypeConverter &typeConverter,
mlir::MLIRContext *context,
cir::LowerModule *lowerModule)
: OpConversionPattern(typeConverter, context), lowerMod(lowerModule) {}

mlir::LogicalResult
matchAndRewrite(cir::StoreOp op, OpAdaptor,
Expand Down
69 changes: 52 additions & 17 deletions clang/test/CIR/CodeGen/const-alloca.cpp
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Original file line number Diff line number Diff line change
@@ -1,5 +1,7 @@
// RUN: %clang_cc1 -triple x86_64-unknown-linux-gnu -fclangir -emit-cir %s -o %t.cir
// RUN: FileCheck --input-file=%t.cir %s
// RUN: %clang_cc1 -triple x86_64-unknown-linux-gnu -O1 -fclangir -emit-cir %s -o %t.cir
// RUN: FileCheck --input-file=%t.cir --check-prefix=CIR %s
// RUN: %clang_cc1 -triple x86_64-unknown-linux-gnu -O1 -fclangir -emit-llvm %s -o %t.ll
// RUN: FileCheck --input-file=%t.ll --check-prefix=LLVM %s

int produce_int();
void blackbox(const int &);
Expand All @@ -8,33 +10,33 @@ void local_const_int() {
const int x = produce_int();
}

// CHECK-LABEL: @_Z15local_const_intv
// CHECK: %{{.+}} = cir.alloca !s32i, !cir.ptr<!s32i>, ["x", init, const]
// CHECK: }
// CIR-LABEL: @_Z15local_const_intv
// CIR: %{{.+}} = cir.alloca !s32i, !cir.ptr<!s32i>, ["x", init, const]
// CIR: }

void param_const_int(const int x) {}

// CHECK-LABEL: @_Z15param_const_inti
// CHECK: %{{.+}} = cir.alloca !s32i, !cir.ptr<!s32i>, ["x", init, const]
// CHECK: }
// CIR-LABEL: @_Z15param_const_inti
// CIR: %{{.+}} = cir.alloca !s32i, !cir.ptr<!s32i>, ["x", init, const]
// CIR: }

void local_constexpr_int() {
constexpr int x = 42;
blackbox(x);
}

// CHECK-LABEL: @_Z19local_constexpr_intv
// CHECK: %{{.+}} = cir.alloca !s32i, !cir.ptr<!s32i>, ["x", init, const]
// CHECK: }
// CIR-LABEL: @_Z19local_constexpr_intv
// CIR: %{{.+}} = cir.alloca !s32i, !cir.ptr<!s32i>, ["x", init, const]
// CIR: }

void local_reference() {
int x = 0;
int &r = x;
}

// CHECK-LABEL: @_Z15local_referencev
// CHECK: %{{.+}} = cir.alloca !cir.ptr<!s32i>, !cir.ptr<!cir.ptr<!s32i>>, ["r", init, const]
// CHECK: }
// CIR-LABEL: @_Z15local_referencev
// CIR: %{{.+}} = cir.alloca !cir.ptr<!s32i>, !cir.ptr<!cir.ptr<!s32i>>, ["r", init, const]
// CIR: }

struct Foo {
int a;
Expand All @@ -47,6 +49,39 @@ void local_const_struct() {
const Foo x = produce_foo();
}

// CHECK-LABEL: @_Z18local_const_structv
// CHECK: %{{.+}} = cir.alloca !ty_Foo, !cir.ptr<!ty_Foo>, ["x", init, const]
// CHECK: }
// CIR-LABEL: @_Z18local_const_structv
// CIR: %{{.+}} = cir.alloca !ty_Foo, !cir.ptr<!ty_Foo>, ["x", init, const]
// CIR: }

[[clang::optnone]]
int local_const_load_store() {
const int x = produce_int();
int y = x;
return y;
}

// CIR-LABEL: @_Z22local_const_load_storev
// CIR: %{{.+}} = cir.alloca !s32i, !cir.ptr<!s32i>, ["x", init, const] {alignment = 4 : i64}
// CIR: }

// LLVM-LABEL: @_Z22local_const_load_storev
// LLVM: %[[#INIT:]] = call i32 @_Z11produce_intv()
// LLVM-NEXT: store i32 %[[#INIT]], ptr %[[#SLOT:]], align 4, !invariant.group !{{.+}}
// LLVM-NEXT: %{{.+}} = load i32, ptr %[[#SLOT]], align 4, !invariant.group !{{.+}}
// LLVM: }

int local_const_optimize() {
const int x = produce_int();
blackbox(x);
blackbox(x);
return x;
}

// LLVM-LABEL: @_Z20local_const_optimizev()
// LLVM-NEXT: %[[#slot:]] = alloca i32, align 4
// LLVM-NEXT: %[[#init:]] = tail call i32 @_Z11produce_intv()
// LLVM-NEXT: store i32 %[[#init]], ptr %[[#slot]], align 4, !invariant.group !{{.+}}
// LLVM-NEXT: call void @_Z8blackboxRKi(ptr nonnull %[[#slot]])
// LLVM-NEXT: call void @_Z8blackboxRKi(ptr nonnull %[[#slot]])
// LLVM-NEXT: ret i32 %[[#init]]
// LLVM-NEXT: }
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