Skip to content

[CIR] Add undef handling to enable global lambdas #169721

New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

Sign up for GitHub

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

Merged
merged 4 commits into from
Nov 26, 2025
Merged

[CIR] Add undef handling to enable global lambdas #169721

Show file tree
Hide file tree
Changes from all commits
Commits
Show all changes
4 commits
Select commit Hold shift + click to select a range
dae3a66
[CIR] Add undef handling to enable global lambdas
andykaylor Nov 26, 2025
fd1f4a2
Minor test update
andykaylor Nov 26, 2025
a2e6808
Fix formatting
andykaylor Nov 26, 2025
45d2d3f
Address review feedback
andykaylor Nov 26, 2025
File filter

Filter by extension

Filter by extension
Conversations
Failed to load comments.
Loading
Jump to
Jump to file
Failed to load files.
Loading
Diff view
Diff view
6 changes: 6 additions & 0 deletions clang/lib/CIR/Dialect/IR/CIRDialect.cpp
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -330,6 +330,12 @@ static LogicalResult checkConstantTypes(mlir::Operation *op, mlir::Type opType,
"zero expects struct, array, vector, or complex type");
}

if (mlir::isa<cir::UndefAttr>(attrType)) {
if (!mlir::isa<cir::VoidType>(opType))
return success();
return op->emitOpError("undef expects non-void type");
}

if (mlir::isa<cir::BoolAttr>(attrType)) {
if (!mlir::isa<cir::BoolType>(opType))
return op->emitOpError("result type (")
Expand Down
22 changes: 16 additions & 6 deletions clang/lib/CIR/Lowering/DirectToLLVM/LowerToLLVM.cpp
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -240,7 +240,7 @@ class CIRAttrToValue {
.Case<cir::IntAttr, cir::FPAttr, cir::ConstComplexAttr,
Copy link
Collaborator

@erichkeane erichkeane Nov 26, 2025

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

Its a Little weird to me that this is a hand-typed list here, and that we don't have some sort of tablegen to get this list? Perhaps a task for a future patch :)

Copy link
Contributor Author

@andykaylor andykaylor Nov 26, 2025

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

We could possibly do that in a way similar to what @Lancern did here: #159390

I'm not sure it's worth the effort though. I don't expect there to ever be a huge number of cases that need to be handled here. This doesn't cover every CIR-specific attribute, only attributes that have a reason (and a way) to be converted to a value in the LLVM dialect. If we had a tablegen for this, we'd still need to provide a CIRAttrToValue::visitCirAttr implementation for anything that wasn't trivially convertible (as IntAttr and FPAttr are).

There are two more in the incubator that we haven't upstreamed yet, bool and poison. I was going to say that I didn't know why we aren't seeing problems related to bool being missing, but I just discovered that it's because we didn't have a test for it (bool initializers for globals are being lowered incorrectly!). I'll fix that shortly.

Copy link
Collaborator

@erichkeane erichkeane Nov 26, 2025

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

Ah, I guess if we're 'near the end' here, that is probably fine. This just looked like the kind of list that would get bad really fast as we grew.

One thing we've done in the past is have the declaration of things like visitCirAttr tablegen'ed, and leave it to the linker to let you know when you've forgotten that. But the lack of compile-time errors on forgetting something like this in a list is unfortunate.

Copy link
Contributor Author

@andykaylor andykaylor Nov 26, 2025

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

On closer inspection, the problem with boolean global initializers is something in the LLVM dialect to LLVM IR translation for the constant. We don't appear to be hitting this visitor for BoolAttr in any case I've found. Maybe it isn't needed.

cir::ConstArrayAttr, cir::ConstRecordAttr, cir::ConstVectorAttr,
cir::ConstPtrAttr, cir::GlobalViewAttr, cir::TypeInfoAttr,
cir::VTableAttr, cir::ZeroAttr>(
cir::UndefAttr, cir::VTableAttr, cir::ZeroAttr>(
[&](auto attrT) { return visitCirAttr(attrT); })
.Default([&](auto attrT) { return mlir::Value(); });
}
Expand All @@ -254,6 +254,7 @@ class CIRAttrToValue {
mlir::Value visitCirAttr(cir::ConstVectorAttr attr);
mlir::Value visitCirAttr(cir::GlobalViewAttr attr);
mlir::Value visitCirAttr(cir::TypeInfoAttr attr);
mlir::Value visitCirAttr(cir::UndefAttr attr);
Copy link
Collaborator

@erichkeane erichkeane Nov 26, 2025

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

This list could/should probably be tablegen'ed/macro'ed too (in a future patch).

mlir::Value visitCirAttr(cir::VTableAttr attr);
mlir::Value visitCirAttr(cir::ZeroAttr attr);

Expand Down Expand Up @@ -591,6 +592,13 @@ mlir::Value CIRAttrToValue::visitCirAttr(cir::TypeInfoAttr typeInfoAttr) {
return result;
}

/// UndefAttr visitor.
mlir::Value CIRAttrToValue::visitCirAttr(cir::UndefAttr undefAttr) {
mlir::Location loc = parentOp->getLoc();
return mlir::LLVM::UndefOp::create(
rewriter, loc, converter->convertType(undefAttr.getType()));
}

// VTableAttr visitor.
mlir::Value CIRAttrToValue::visitCirAttr(cir::VTableAttr vtableArr) {
mlir::Type llvmTy = converter->convertType(vtableArr.getType());
Expand Down Expand Up @@ -2046,9 +2054,11 @@ CIRToLLVMGlobalOpLowering::matchAndRewriteRegionInitializedGlobal(
cir::GlobalOp op, mlir::Attribute init,
mlir::ConversionPatternRewriter &rewriter) const {
// TODO: Generalize this handling when more types are needed here.
assert((isa<cir::ConstArrayAttr, cir::ConstRecordAttr, cir::ConstVectorAttr,
cir::ConstPtrAttr, cir::ConstComplexAttr, cir::GlobalViewAttr,
cir::TypeInfoAttr, cir::VTableAttr, cir::ZeroAttr>(init)));
assert(
(isa<cir::ConstArrayAttr, cir::ConstRecordAttr, cir::ConstVectorAttr,
cir::ConstPtrAttr, cir::ConstComplexAttr, cir::GlobalViewAttr,
cir::TypeInfoAttr, cir::UndefAttr, cir::VTableAttr, cir::ZeroAttr>(
init)));

// TODO(cir): once LLVM's dialect has proper equivalent attributes this
// should be updated. For now, we use a custom op to initialize globals
Expand Down Expand Up @@ -2106,8 +2116,8 @@ mlir::LogicalResult CIRToLLVMGlobalOpLowering::matchAndRewrite(
} else if (mlir::isa<cir::ConstArrayAttr, cir::ConstVectorAttr,
cir::ConstRecordAttr, cir::ConstPtrAttr,
cir::ConstComplexAttr, cir::GlobalViewAttr,
cir::TypeInfoAttr, cir::VTableAttr, cir::ZeroAttr>(
init.value())) {
cir::TypeInfoAttr, cir::UndefAttr, cir::VTableAttr,
cir::ZeroAttr>(init.value())) {
// TODO(cir): once LLVM's dialect has proper equivalent attributes this
// should be updated. For now, we use a custom op to initialize globals
// to the appropriate value.
Expand Down
33 changes: 33 additions & 0 deletions clang/test/CIR/CodeGen/lambda.cpp
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -8,6 +8,39 @@
// We declare anonymous record types to represent lambdas. Rather than trying to
// to match the declarations, we establish variables for these when they are used.

auto global_lambda = [](){};
void use_global_lambda() {
global_lambda();
}

// CIR: cir.global "private" internal dso_local @global_lambda = #cir.undef : ![[REC_LAM_GLOBAL_LAMBDA:.*]] {alignment = 1 : i64}
// CIR: cir.func lambda internal private dso_local @_ZNK3$_0clEv(%[[THIS_ARG:.*]]: !cir.ptr<![[REC_LAM_GLOBAL_LAMBDA]]> {{.*}})
// CIR: %[[THIS:.*]] = cir.alloca !cir.ptr<![[REC_LAM_GLOBAL_LAMBDA]]>, !cir.ptr<!cir.ptr<![[REC_LAM_GLOBAL_LAMBDA]]>>, ["this", init]
// CIR: cir.store %[[THIS_ARG]], %[[THIS]]
// CIR: cir.load %[[THIS]]
//
// CIR: cir.func {{.*}} @_Z17use_global_lambdav()
// CIR: %[[LAMBDA:.*]] = cir.get_global @global_lambda : !cir.ptr<![[REC_LAM_GLOBAL_LAMBDA]]>
// CIR: cir.call @_ZNK3$_0clEv(%[[LAMBDA]]) : (!cir.ptr<![[REC_LAM_GLOBAL_LAMBDA]]>) -> ()

// LLVM: @global_lambda = internal global %[[REC_LAM_GLOBAL_LAMBDA:.*]] undef, align 1
// LLVM: define internal void @"_ZNK3$_0clEv"(ptr %[[THIS_ARG:.*]])
// LLVM: %[[THIS_ADDR:.*]] = alloca ptr
// LLVM: store ptr %[[THIS_ARG]], ptr %[[THIS_ADDR]]
// LLVM: %[[THIS:.*]] = load ptr, ptr %[[THIS_ADDR]]
//
// LLVM: define dso_local void @_Z17use_global_lambdav()
// LLVM: call void @"_ZNK3$_0clEv"(ptr @global_lambda)

// OGCG: @global_lambda = internal global %[[REC_LAM_GLOBAL_LAMBDA:.*]] undef, align 1
// OGCG: define dso_local void @_Z17use_global_lambdav()
// OGCG: call void @"_ZNK3$_0clEv"(ptr noundef nonnull align 1 dereferenceable(1) @global_lambda)
//
// OGCG: define internal void @"_ZNK3$_0clEv"(ptr {{.*}} %[[THIS_ARG:.*]])
// OGCG: %[[THIS_ADDR:.*]] = alloca ptr
// OGCG: store ptr %[[THIS_ARG]], ptr %[[THIS_ADDR]]
// OGCG: %[[THIS:.*]] = load ptr, ptr %[[THIS_ADDR]]

void fn() {
auto a = [](){};
a();
Expand Down
Loading