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[CIR] Upstream trivial constructor const handling #164849

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merged 2 commits into from
Oct 24, 2025
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[CIR] Upstream trivial constructor const handling #164849

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[CIR] Upstream trivial constructor const handling
andykaylor Oct 22, 2025
20b47cd
Add marker for future investigation
andykaylor Oct 24, 2025
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3 changes: 1 addition & 2 deletions clang/lib/CIR/CodeGen/CIRGenExprAggregate.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -362,8 +362,7 @@ class AggExprEmitter : public StmtVisitor<AggExprEmitter> {
cgf.cgm.errorNYI(e->getSourceRange(), "AggExprEmitter: VisitCXXTypeidExpr");
}
void VisitMaterializeTemporaryExpr(MaterializeTemporaryExpr *e) {
cgf.cgm.errorNYI(e->getSourceRange(),
"AggExprEmitter: VisitMaterializeTemporaryExpr");
Visit(e->getSubExpr());
}
void VisitOpaqueValueExpr(OpaqueValueExpr *e) {
cgf.cgm.errorNYI(e->getSourceRange(),
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24 changes: 21 additions & 3 deletions clang/lib/CIR/CodeGen/CIRGenExprConstant.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -1069,9 +1069,27 @@ class ConstExprEmitter

mlir::Attribute VisitCXXConstructExpr(CXXConstructExpr *e, QualType ty) {
if (!e->getConstructor()->isTrivial())
return nullptr;
cgm.errorNYI(e->getBeginLoc(), "trivial constructor const handling");
return {};
return {};

// Only default and copy/move constructors can be trivial.
if (e->getNumArgs()) {
assert(e->getNumArgs() == 1 && "trivial ctor with > 1 argument");
assert(e->getConstructor()->isCopyOrMoveConstructor() &&
"trivial ctor has argument but isn't a copy/move ctor");

Expr *arg = e->getArg(0);
assert(cgm.getASTContext().hasSameUnqualifiedType(ty, arg->getType()) &&
"argument to copy ctor is of wrong type");

// Look through the temporary; it's just converting the value to an lvalue
// to pass it to the constructor.
if (auto const *mte = dyn_cast<MaterializeTemporaryExpr>(arg))
return Visit(mte->getSubExpr(), ty);
// Don't try to support arbitrary lvalue-to-rvalue conversions for now.
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@erichkeane erichkeane Oct 23, 2025

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Should this be a not-yet-implemented or something?

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@andykaylor andykaylor Oct 23, 2025

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This comment is carried over from classic codegen, which does the same thing here.

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@erichkeane erichkeane Oct 23, 2025

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Oh weird... Can you replace the dyn_cast with a cast in classic codegen? Does it hit anything? I'm actually pretty concerned by this...

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@andykaylor andykaylor Oct 23, 2025

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If I report and error after the dyn_cast falls through in classic codegen, it fires 14 times in eight tests in the CodeGenCXX tests:

llvm-project/clang/test/CodeGenCXX/microsoft-uuidof.cpp

Line 44 in a909ec6

GUID thing = (side_effect(), __uuidof(Curly));

llvm-project/clang/test/CodeGenCXX/cxx0x-initializer-stdinitializerlist.cpp

Line 214 in a909ec6

target({ inner, { destroyme1() } });

llvm-project/clang/test/CodeGenCXX/cxx0x-initializer-stdinitializerlist.cpp

Line 245 in a909ec6

(void) new std::initializer_list<int> {i, 2, 3};

llvm-project/clang/test/CodeGenCXX/cxx0x-initializer-stdinitializerlist.cpp

Line 250 in a909ec6

(void) new std::initializer_list<destroyme1> {destroyme1(), destroyme1()};

llvm-project/clang/test/CodeGenCXX/cxx0x-initializer-stdinitializerlist.cpp

Line 304 in a909ec6

std::initializer_list<S>{ S(), S() };

llvm-project/clang/test/CodeGenCXX/cxx0x-initializer-stdinitializerlist.cpp

Line 321 in a909ec6

auto x = std::initializer_list<S>{ S(), S() };

llvm-project/clang/test/CodeGenCXX/atomicinit.cpp

Line 117 in a909ec6

Y y2 = { x, z };

llvm-project/clang/test/CodeGenCXX/reference-init.cpp

Line 38 in a909ec6

SelfReference self_reference_2 = {self_reference_1};

llvm-project/clang/test/CodeGenCXX/aix-static-init-temp-spec-and-inline-var.cpp

Line 44 in a909ec6

A<int> A<int>::instance = bar();

llvm-project/clang/test/CodeGenCXX/cxx1z-decomposition.cpp

Line 34 in a909ec6

auto [a1, a2] = make<A>();

llvm-project/clang/test/CodeGenCXX/cxx1z-decomposition.cpp

Line 122 in a909ec6

static auto [x1, x2] = make<A>();

llvm-project/clang/test/CodeGenCXX/cxx1z-decomposition.cpp

Line 138 in a909ec6

static auto [x1, x2] = make<B>();

llvm-project/clang/test/CodeGenCXX/static-init-3.cpp

Line 27 in a909ec6

X2< B > bg = X1< X2< B > >::get();

llvm-project/clang/test/CodeGenCXX/copy-constructor-synthesis-2.cpp

Line 11 in a909ec6

PR23373 pr23373_b(pr23373_a);

I haven't looked at these in detail yet, but I know that we can get here if the constructor argument is not a constant, and if we do then returning nullptr is the correct behavior.

The only case that would be a problem is if the argument is not a MaterializeTemporaryExpr but is a constant, and even in that case if we return null here, something else is going to handle it, though possibly not correctly.

I also tried inserting a call to ConstantExprEmitter::Visit(Arg, Ty) in the case where the dyn_cast failed, and that doesn't change anything.

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@bcardosolopes bcardosolopes Oct 23, 2025

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One possible alternative is to add a missing feature as a way to track what needs to be investigated into both CodeGen paths.

return {};
}

return cgm.getBuilder().getZeroInitAttr(cgm.convertType(ty));
}

mlir::Attribute VisitStringLiteral(StringLiteral *e, QualType t) {
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44 changes: 44 additions & 0 deletions clang/test/CIR/CodeGen/trivial-ctor-const-init.cpp
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Original file line number Diff line number Diff line change
@@ -0,0 +1,44 @@
// RUN: %clang_cc1 -triple x86_64-unknown-linux-gnu -std=c++11 -fclangir -emit-cir %s -o %t.cir
// RUN: FileCheck --input-file=%t.cir %s --check-prefix=CIR
// RUN: %clang_cc1 -triple x86_64-unknown-linux-gnu -std=c++11 -fclangir -emit-llvm %s -o %t-cir.ll
// RUN: FileCheck --input-file=%t-cir.ll %s --check-prefix=LLVM
// RUN: %clang_cc1 -triple x86_64-unknown-linux-gnu -std=c++11 -emit-llvm %s -o %t.ll
// RUN: FileCheck --input-file=%t.ll %s --check-prefix=OGCG

struct StructWithDefaultCtor {
int n;
};

StructWithDefaultCtor defCtor = StructWithDefaultCtor();

// CIR: cir.global {{.*}} @defCtor = #cir.zero : !rec_StructWithDefaultCtor
// LLVM: @defCtor = global %struct.StructWithDefaultCtor zeroinitializer
// OGCG: @defCtor = global %struct.StructWithDefaultCtor zeroinitializer

struct StructWithCtorArg {
double value;
StructWithCtorArg(const double& x) : value(x) {}
};

StructWithCtorArg withArg = 0.0;

// CIR: cir.global {{.*}} @withArg = #cir.zero : !rec_StructWithCtorArg
// LLVM: @withArg = global %struct.StructWithCtorArg zeroinitializer
// OGCG: @withArg = global %struct.StructWithCtorArg zeroinitializer

// CIR: cir.func {{.*}} @__cxx_global_var_init()
// CIR: %[[TMP0:.*]] = cir.alloca !cir.double, !cir.ptr<!cir.double>, ["ref.tmp0"]
// CIR: %[[WITH_ARG:.*]] = cir.get_global @withArg : !cir.ptr<!rec_StructWithCtorArg>
// CIR: %[[ZERO:.*]] = cir.const #cir.fp<0.000000e+00> : !cir.double
// CIR: cir.store{{.*}} %[[ZERO]], %[[TMP0]] : !cir.double, !cir.ptr<!cir.double>
// CIR: cir.call @_ZN17StructWithCtorArgC1ERKd(%[[WITH_ARG]], %[[TMP0]]) : (!cir.ptr<!rec_StructWithCtorArg>, !cir.ptr<!cir.double>) -> ()

// LLVM: define {{.*}} void @__cxx_global_var_init()
// LLVM: %[[TMP0:.*]] = alloca double
// LLVM: store double 0.000000e+00, ptr %[[TMP0]]
// LLVM: call void @_ZN17StructWithCtorArgC1ERKd(ptr @withArg, ptr %[[TMP0]])

// OGCG: define {{.*}} void @__cxx_global_var_init()
// OGCG: %[[TMP0:.*]] = alloca double
// OGCG: store double 0.000000e+00, ptr %[[TMP0]]
// OGCG: call void @_ZN17StructWithCtorArgC1ERKd(ptr {{.*}} @withArg, ptr {{.*}} %[[TMP0]])
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