[clang] 012680f - [clang][Expr] Teach IgnoreUnlessSpelledInSource about implicit calls to std::get free function (#122265)
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cfe-commits at lists.llvm.org
Sat Sep 20 10:30:22 PDT 2025
Author: Michael Buch
Date: 2025-09-20T18:30:18+01:00
New Revision: 012680faf4c63a9bd432aa92fa0da97981793ac3
URL: https://github.com/llvm/llvm-project/commit/012680faf4c63a9bd432aa92fa0da97981793ac3
DIFF: https://github.com/llvm/llvm-project/commit/012680faf4c63a9bd432aa92fa0da97981793ac3.diff
LOG: [clang][Expr] Teach IgnoreUnlessSpelledInSource about implicit calls to std::get free function (#122265)
When we generate the debug-info for a `VarDecl` we try to determine
whether it was introduced as part of a structure binding (aka a "holding
var"). If it was then we don't mark it as `artificial`.
The heuristic to determine a holding var uses
`IgnoreUnlessSpelledInSource` to unwrap the `VarDecl` initializer until
we hit a `DeclRefExpr` that refers to a `Decomposition`. For "tuple-like
decompositions", Clang will generate a call to a `template<size_t I> Foo
get(Bar)` function that retrieves the `Ith` element from the tuple-like
structure. If that function is a member function, we get an AST that
looks as follows:
```
VarDecl implicit used z1 'std::tuple_element<0, B>::type &&' cinit
`-ExprWithCleanups <col:10> 'int' xvalue
`-MaterializeTemporaryExpr <col:10> 'int' xvalue extended by Var 0x11d110cf8 'z1' 'std::tuple_element<0, B>::type &&'
`-CXXMemberCallExpr <col:10> 'int'
`-MemberExpr <col:10> '<bound member function type>' .get 0x11d104390
`-ImplicitCastExpr <col:10> 'B' xvalue <NoOp>
`-DeclRefExpr <col:10> 'B' lvalue Decomposition 0x11d1100a8 '' 'B'
```
`IgnoreUnlessSpelledInSource` happily unwraps this down to the
`DeclRefExpr`. However, when the `get` helper is a free function (which
it is for `std::pair` in libc++ for example), then the AST is:
```
VarDecl col:16 implicit used k 'std::tuple_element<0, const std::tuple<int, int>>::type &' cinit
`-CallExpr <col:16> 'const typename tuple_element<0UL, tuple<int, int>>::type':'const int' lvalue adl
|-ImplicitCastExpr <col:16> 'const typename tuple_element<0UL, tuple<int, int>>::type &(*)(const tuple<int, int> &) noexcept' <FunctionToPointerDecay>
| `-DeclRefExpr <col:16> 'const typename tuple_element<0UL, tuple<int, int>>::type &(const tuple<int, int> &) noexcept' lvalue Function 0x1210262d8 'get' 'const typename tuple_element<0UL, tuple<int, int>>::type &(const tuple<int, int> &) noexcept' (FunctionTemplate 0x11d068088 'get')
`-DeclRefExpr <col:16> 'const std::tuple<int, int>' lvalue Decomposition 0x121021518 '' 'const std::tuple<int, int> &'
```
`IgnoreUnlessSpelledInSource` doesn't unwrap this `CallExpr`, so we
incorrectly mark the binding as `artificial` in debug-info.
This patch adjusts `IgnoreUnlessSpelledInSource` so it unwraps implicit
`CallExpr`s. It's almost identical to how we treat implicit constructor
calls (unfortunately the code can't quite be re-used because a
`CXXConstructExpr` is-not a `CallExpr`, and we check `isElidable`, which
doesn't exist for regular function calls. So I added a new
`IgnoreImplicitCallSingleStep`).
Fixes https://github.com/llvm/llvm-project/issues/122028
Added:
Modified:
clang/lib/AST/Expr.cpp
clang/test/DebugInfo/CXX/structured-binding.cpp
clang/unittests/AST/ASTTraverserTest.cpp
lldb/test/API/lang/cpp/structured-binding/TestStructuredBinding.py
lldb/test/API/lang/cpp/structured-binding/main.cpp
Removed:
################################################################################
diff --git a/clang/lib/AST/Expr.cpp b/clang/lib/AST/Expr.cpp
index cdff160067fed..6ef7e54ec00b9 100644
--- a/clang/lib/AST/Expr.cpp
+++ b/clang/lib/AST/Expr.cpp
@@ -2545,6 +2545,18 @@ Stmt *BlockExpr::getBody() {
// Generic Expression Routines
//===----------------------------------------------------------------------===//
+/// Helper to determine wether \c E is a CXXConstructExpr constructing
+/// a DecompositionDecl. Used to skip Clang-generated calls to std::get
+/// for structured bindings.
+static bool IsDecompositionDeclRefExpr(const Expr *E) {
+ const auto *Unwrapped = E->IgnoreUnlessSpelledInSource();
+ const auto *Ref = dyn_cast<DeclRefExpr>(Unwrapped);
+ if (!Ref)
+ return false;
+
+ return isa_and_nonnull<DecompositionDecl>(Ref->getDecl());
+}
+
bool Expr::isReadIfDiscardedInCPlusPlus11() const {
// In C++11, discarded-value expressions of a certain form are special,
// according to [expr]p10:
@@ -3159,10 +3171,39 @@ Expr *Expr::IgnoreUnlessSpelledInSource() {
}
return E;
};
+
+ // Used when Clang generates calls to std::get for decomposing
+ // structured bindings.
+ auto IgnoreImplicitCallSingleStep = [](Expr *E) {
+ auto *C = dyn_cast<CallExpr>(E);
+ if (!C)
+ return E;
+
+ // Looking for calls to a std::get, which usually just takes
+ // 1 argument (i.e., the structure being decomposed). If it has
+ // more than 1 argument, the others need to be defaulted.
+ unsigned NumArgs = C->getNumArgs();
+ if (NumArgs == 0 || (NumArgs > 1 && !isa<CXXDefaultArgExpr>(C->getArg(1))))
+ return E;
+
+ Expr *A = C->getArg(0);
+
+ // This was spelled out in source. Don't ignore.
+ if (A->getSourceRange() != E->getSourceRange())
+ return E;
+
+ // If the argument refers to a DecompositionDecl construction,
+ // ignore it.
+ if (IsDecompositionDeclRefExpr(A))
+ return A;
+
+ return E;
+ };
+
return IgnoreExprNodes(
this, IgnoreImplicitSingleStep, IgnoreImplicitCastsExtraSingleStep,
IgnoreParensOnlySingleStep, IgnoreImplicitConstructorSingleStep,
- IgnoreImplicitMemberCallSingleStep);
+ IgnoreImplicitMemberCallSingleStep, IgnoreImplicitCallSingleStep);
}
bool Expr::isDefaultArgument() const {
diff --git a/clang/test/DebugInfo/CXX/structured-binding.cpp b/clang/test/DebugInfo/CXX/structured-binding.cpp
index 8032ce85c9e25..95457f477deeb 100644
--- a/clang/test/DebugInfo/CXX/structured-binding.cpp
+++ b/clang/test/DebugInfo/CXX/structured-binding.cpp
@@ -1,5 +1,6 @@
-// RUN: %clang_cc1 -emit-llvm -debug-info-kind=standalone -triple %itanium_abi_triple %s -o - | FileCheck %s --implicit-check-not="call void @llvm.dbg.declare"
+// RUN: %clang_cc1 -std=c++23 -emit-llvm -debug-info-kind=standalone -triple %itanium_abi_triple %s -o - | FileCheck %s --implicit-check-not="call void @llvm.dbg.declare"
+// CHECK: define {{.*}} i32 @_Z1fv
// CHECK: #dbg_declare(ptr %{{[a-z]+}}, ![[VAR_0:[0-9]+]], !DIExpression(),
// CHECK: #dbg_declare(ptr %{{[0-9]+}}, ![[VAR_1:[0-9]+]], !DIExpression(),
// CHECK: #dbg_declare(ptr %{{[0-9]+}}, ![[VAR_2:[0-9]+]], !DIExpression(DW_OP_plus_uconst, 4),
@@ -7,6 +8,13 @@
// CHECK: #dbg_declare(ptr %{{[0-9]+}}, ![[VAR_4:[0-9]+]], !DIExpression(DW_OP_deref, DW_OP_plus_uconst, 4),
// CHECK: #dbg_declare(ptr %z1, ![[VAR_5:[0-9]+]], !DIExpression()
// CHECK: #dbg_declare(ptr %z2, ![[VAR_6:[0-9]+]], !DIExpression()
+// CHECK: #dbg_declare(ptr %k, ![[VAR_7:[0-9]+]], !DIExpression()
+// CHECK: #dbg_declare(ptr %v, ![[VAR_8:[0-9]+]], !DIExpression()
+// CHECK: #dbg_declare(ptr %w, ![[VAR_9:[0-9]+]], !DIExpression()
+// CHECK: #dbg_declare(ptr %m, ![[VAR_10:[0-9]+]], !DIExpression()
+// CHECK: #dbg_declare(ptr %n, ![[VAR_11:[0-9]+]], !DIExpression()
+// CHECK: #dbg_declare(ptr %s, ![[VAR_12:[0-9]+]], !DIExpression()
+// CHECK: #dbg_declare(ptr %p, ![[VAR_13:[0-9]+]], !DIExpression()
// CHECK: getelementptr inbounds nuw %struct.A, ptr {{.*}}, i32 0, i32 1, !dbg ![[Y1_DEBUG_LOC:[0-9]+]]
// CHECK: getelementptr inbounds nuw %struct.A, ptr {{.*}}, i32 0, i32 1, !dbg ![[Y2_DEBUG_LOC:[0-9]+]]
// CHECK: load ptr, ptr %z2, {{.*}}!dbg ![[Z2_DEBUG_LOC:[0-9]+]]
@@ -20,6 +28,13 @@
// CHECK: ![[VAR_4]] = !DILocalVariable(name: "y2", scope: !{{[0-9]+}}, file: !{{[0-9]+}}, line: {{[0-9]+}}, type: !{{[0-9]+}})
// CHECK: ![[VAR_5]] = !DILocalVariable(name: "z1", scope: !{{[0-9]+}}, file: !{{[0-9]+}}, line: {{[0-9]+}}, type: !{{[0-9]+}})
// CHECK: ![[VAR_6]] = !DILocalVariable(name: "z2", scope: !{{[0-9]+}}, file: !{{[0-9]+}}, line: {{[0-9]+}}, type: !{{[0-9]+}})
+// CHECK: ![[VAR_7]] = !DILocalVariable(name: "k", scope: !{{[0-9]+}}, file: !{{[0-9]+}}, line: {{[0-9]+}}, type: !{{[0-9]+}})
+// CHECK: ![[VAR_8]] = !DILocalVariable(name: "v", scope: !{{[0-9]+}}, file: !{{[0-9]+}}, line: {{[0-9]+}}, type: !{{[0-9]+}})
+// CHECK: ![[VAR_9]] = !DILocalVariable(name: "w", scope: !{{[0-9]+}}, file: !{{[0-9]+}}, line: {{[0-9]+}}, type: !{{[0-9]+}})
+// CHECK: ![[VAR_10]] = !DILocalVariable(name: "m", scope: !{{[0-9]+}}, file: !{{[0-9]+}}, line: {{[0-9]+}}, type: !{{[0-9]+}})
+// CHECK: ![[VAR_11]] = !DILocalVariable(name: "n", scope: !{{[0-9]+}}, file: !{{[0-9]+}}, line: {{[0-9]+}}, type: !{{[0-9]+}})
+// CHECK: ![[VAR_12]] = !DILocalVariable(name: "s", scope: !{{[0-9]+}}, file: !{{[0-9]+}}, line: {{[0-9]+}}, type: !{{[0-9]+}})
+// CHECK: ![[VAR_13]] = !DILocalVariable(name: "p", scope: !{{[0-9]+}}, file: !{{[0-9]+}}, line: {{[0-9]+}}, type: !{{[0-9]+}})
struct A {
int x;
@@ -34,6 +49,22 @@ struct B {
template<> int get<1>() { return z; }
};
+struct C {
+ int w;
+ int z;
+ template<int> int get(this C&& self);
+ template<> int get<0>(this C&& self) { return self.w; }
+ template<> int get<1>(this C&& self) { return self.z; }
+};
+
+struct D {
+ int w;
+ int z;
+ template<int> int get(int unused = 0);
+ template<> int get<0>(int unused) { return w; }
+ template<> int get<1>(int unused) { return z; }
+};
+
// Note: the following declarations are necessary for decomposition of tuple-like
// structured bindings
namespace std {
@@ -44,7 +75,35 @@ struct tuple_size<B> {
static constexpr unsigned value = 2;
};
+template<>
+struct tuple_size<C> {
+ static constexpr unsigned value = 2;
+};
+
+template<>
+struct tuple_size<D> {
+ static constexpr unsigned value = 2;
+};
+
template<unsigned, typename T> struct tuple_element { using type = int; };
+
+// Decomposition of tuple-like bindings but where the `get` methods
+// are declared as free functions.
+struct triple {
+ int k;
+ int v;
+ int w;
+};
+
+template<>
+struct tuple_size<triple> {
+ static constexpr unsigned value = 3;
+};
+
+template <unsigned I> int get(triple);
+template <> int get<0>(triple p) { return p.k; }
+template <> int get<1>(triple p) { return p.v; }
+template <> int get<2>(triple p) { return p.w; }
} // namespace std
int f() {
@@ -58,6 +117,9 @@ int f() {
auto &[c1, c2] = cmplx;
int vctr __attribute__ ((vector_size (sizeof(int)*2)))= {1, 2};
auto &[v1, v2] = vctr;
+ auto [k, v, w] = std::triple{3, 4, 5};
+ auto [m, n] = C{2, 3};
+ auto [s, p] = D{2, 3};
return //
x1 //
+ //
diff --git a/clang/unittests/AST/ASTTraverserTest.cpp b/clang/unittests/AST/ASTTraverserTest.cpp
index 988e81d8e51de..bcbf01b6b0385 100644
--- a/clang/unittests/AST/ASTTraverserTest.cpp
+++ b/clang/unittests/AST/ASTTraverserTest.cpp
@@ -1174,6 +1174,12 @@ struct Pair
int x, y;
};
+// Tuple-like structure with a `get` method that has a default argument.
+struct Pair2
+{
+ int x, y;
+};
+
// Note: these utilities are required to force binding to tuple like structure
namespace std
{
@@ -1188,6 +1194,12 @@ namespace std
static constexpr size_t value = 2;
};
+ template <>
+ struct tuple_size<Pair2>
+ {
+ static constexpr size_t value = 2;
+ };
+
template <size_t I, class T>
struct tuple_element
{
@@ -1199,12 +1211,17 @@ namespace std
template <size_t I>
int &&get(Pair &&p);
+template <size_t I>
+int &&get(Pair2 &&p, int unused = 0);
+
void decompTuple()
{
Pair p{1, 2};
auto [a, b] = p;
a = 3;
+
+ auto [c, d] = Pair2{3, 4};
}
)cpp",
@@ -1586,6 +1603,62 @@ DecompositionDecl ''
|-DeclRefExpr 'p'
|-BindingDecl 'a'
`-BindingDecl 'b'
+)cpp");
+ }
+
+ {
+ auto FN = ast_matchers::match(
+ functionDecl(hasName("decompTuple"),
+ hasDescendant(callExpr(hasAncestor(varDecl(
+ hasName("a"),
+ hasAncestor(bindingDecl()))))
+ .bind("decomp_call"))),
+ AST2->getASTContext());
+ EXPECT_EQ(FN.size(), 1u);
+
+ EXPECT_EQ(dumpASTString(TK_AsIs, FN[0].getNodeAs<CallExpr>("decomp_call")),
+ R"cpp(
+CallExpr
+|-ImplicitCastExpr
+| `-DeclRefExpr 'get'
+`-ImplicitCastExpr
+ `-DeclRefExpr ''
+)cpp");
+
+ EXPECT_EQ(dumpASTString(TK_IgnoreUnlessSpelledInSource,
+ FN[0].getNodeAs<CallExpr>("decomp_call")),
+ R"cpp(
+DeclRefExpr ''
+)cpp");
+ }
+
+ {
+ auto FN = ast_matchers::match(
+ functionDecl(hasName("decompTuple"),
+ hasDescendant(callExpr(hasAncestor(varDecl(
+ hasName("c"),
+ hasAncestor(bindingDecl()))))
+ .bind("decomp_call_with_default"))),
+ AST2->getASTContext());
+ EXPECT_EQ(FN.size(), 1u);
+
+ EXPECT_EQ(dumpASTString(TK_AsIs, FN[0].getNodeAs<CallExpr>(
+ "decomp_call_with_default")),
+ R"cpp(
+CallExpr
+|-ImplicitCastExpr
+| `-DeclRefExpr 'get'
+|-ImplicitCastExpr
+| `-DeclRefExpr ''
+`-CXXDefaultArgExpr
+ `-IntegerLiteral
+)cpp");
+
+ EXPECT_EQ(
+ dumpASTString(TK_IgnoreUnlessSpelledInSource,
+ FN[0].getNodeAs<CallExpr>("decomp_call_with_default")),
+ R"cpp(
+DeclRefExpr ''
)cpp");
}
}
diff --git a/lldb/test/API/lang/cpp/structured-binding/TestStructuredBinding.py b/lldb/test/API/lang/cpp/structured-binding/TestStructuredBinding.py
index 1e026cf8c237c..5f939ecfbef29 100644
--- a/lldb/test/API/lang/cpp/structured-binding/TestStructuredBinding.py
+++ b/lldb/test/API/lang/cpp/structured-binding/TestStructuredBinding.py
@@ -98,3 +98,17 @@ def test(self):
self.expect_expr("tx2", result_value="4")
self.expect_expr("ty2", result_value="'z'")
self.expect_expr("tz2", result_value="10")
+
+ self.expect(
+ "frame variable",
+ substrs=[
+ "tx1 =",
+ "ty1 =",
+ "tz1 =",
+ "tx2 =",
+ "ty2 =",
+ "tz2 =",
+ "mp1 =",
+ "mp2 =",
+ ],
+ )
diff --git a/lldb/test/API/lang/cpp/structured-binding/main.cpp b/lldb/test/API/lang/cpp/structured-binding/main.cpp
index 3fbfb18dbeff0..b649358ebdf66 100644
--- a/lldb/test/API/lang/cpp/structured-binding/main.cpp
+++ b/lldb/test/API/lang/cpp/structured-binding/main.cpp
@@ -1,13 +1,80 @@
// Structured binding in C++ can bind identifiers to subobjects of an object.
//
-// There are three cases we need to test:
+// There are four cases we need to test:
// 1) arrays
-// 2) tuples like objects
-// 3) non-static data members
+// 2) tuple-like objects with `get` member functions
+// 3) tuple-like objects with `get` free functions
+// 4) non-static data members
//
// They can also bind by copy, reference or rvalue reference.
-#include <tuple>
+struct MyPair {
+ int m1;
+ int m2;
+
+ // Helpers to enable tuple-like decomposition.
+ template <unsigned> int get();
+ template <> int get<0>() { return m1; }
+ template <> int get<1>() { return m2; }
+};
+
+namespace std {
+template <typename T1, typename T2, typename T3> struct mock_tuple {
+ T1 m1;
+ T2 m2;
+ T3 m3;
+};
+
+template <typename T> struct tuple_size;
+
+template <unsigned, typename T> struct tuple_element;
+
+// Helpers to enable tuple-like decomposition for MyPair
+template <unsigned I> struct tuple_element<I, MyPair> {
+ using type = int;
+};
+
+template <> struct tuple_size<MyPair> {
+ static constexpr unsigned value = 2;
+};
+
+// Helpers to enable tuple-like decomposition for mock_tuple
+template <typename T1, typename T2, typename T3>
+struct tuple_element<0, mock_tuple<T1, T2, T3>> {
+ using type = T1;
+};
+
+template <typename T1, typename T2, typename T3>
+struct tuple_element<1, mock_tuple<T1, T2, T3>> {
+ using type = T2;
+};
+
+template <typename T1, typename T2, typename T3>
+struct tuple_element<2, mock_tuple<T1, T2, T3>> {
+ using type = T3;
+};
+
+template <typename T1, typename T2, typename T3>
+struct tuple_size<mock_tuple<T1, T2, T3>> {
+ static constexpr unsigned value = 3;
+};
+
+template <unsigned I, typename T1, typename T2, typename T3>
+typename tuple_element<I, mock_tuple<T1, T2, T3>>::type
+get(mock_tuple<T1, T2, T3> p) {
+ switch (I) {
+ case 0:
+ return p.m1;
+ case 1:
+ return p.m2;
+ case 2:
+ return p.m3;
+ default:
+ __builtin_trap();
+ }
+}
+
+} // namespace std
struct A {
int x;
@@ -54,10 +121,12 @@ int main() {
char y{'z'};
int z{10};
- std::tuple<float, char, int> tpl(x, y, z);
+ std::mock_tuple<float, char, int> tpl{.m1 = x, .m2 = y, .m3 = z};
auto [tx1, ty1, tz1] = tpl;
auto &[tx2, ty2, tz2] = tpl;
+ auto [mp1, mp2] = MyPair{.m1 = 1, .m2 = 2};
+
return a1.x + b1 + c1 + d1 + e1 + f1 + a2.y + b2 + c2 + d2 + e2 + f2 + a3.x +
b3 + c3 + d3 + e3 + f3 + carr_copy1 + carr_copy2 + carr_copy3 +
sarr_copy1 + sarr_copy2 + sarr_copy3 + iarr_copy1 + iarr_copy2 +
@@ -65,5 +134,5 @@ int main() {
sarr_ref2 + sarr_ref3 + iarr_ref1 + iarr_ref2 + iarr_ref3 +
carr_rref1 + carr_rref2 + carr_rref3 + sarr_rref1 + sarr_rref2 +
sarr_rref3 + iarr_rref1 + iarr_rref2 + iarr_rref3 + tx1 + ty1 + tz1 +
- tx2 + ty2 + tz2; // break here
+ tx2 + ty2 + tz2 + mp1 + mp2; // break here
}
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