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C++ interop: support for default arguments. (#6108)

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The general strategy here is to force use of a thunk when we want to use
default arguments, and have Clang generate uses of the default arguments
on its side of the thunk.

To support this, change the key type used in `clang_decls` from being
just a `Decl*` to being a pair of `Decl*` and number of parameters in
the case of function decls. Import distinct `SemIR::Function`s for each
number of parameters that's used, and corresponding distinct thunks.

---------

Co-authored-by: Jon Ross-Perkins <jperkins@google.com>
This commit is contained in:
Richard Smith
2025-09-24 01:07:59 +00:00
committed by GitHub
co-authored by Jon Ross-Perkins
parent 82679e6689
commit 1e7b7e53ae
42 changed files with 2097 additions and 720 deletions
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toolchain/lower/testdata/interop/cpp/function_decl.carbon
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+72 -1
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@@ -2,7 +2,7 @@
// Exceptions. See /LICENSE for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
// INCLUDE-FILE: toolchain/testing/testdata/min_prelude/convert.carbon
// INCLUDE-FILE: toolchain/testing/testdata/min_prelude/int.carbon
//
// AUTOUPDATE
// TIP: To test this file alone, run:
@@ -106,6 +106,26 @@ fn MyF() {
Cpp.foo2();
}
// ============================================================================
// Default arguments
// ============================================================================
// --- with_default_args.h
void F(int a = 1, int b = 2);
// --- call_with_default_args.carbon
library "[[@TEST_NAME]]";
import Cpp library "with_default_args.h";
fn MyF() {
Cpp.F();
Cpp.F(3);
Cpp.F(3, 4);
}
// CHECK:STDOUT: ; ModuleID = 'import_function_decl.carbon'
// CHECK:STDOUT: source_filename = "import_function_decl.carbon"
// CHECK:STDOUT: target datalayout = "e-m:e-p270:32:32-p271:32:32-p272:64:64-i64:64-i128:128-f80:128-n8:16:32:64-S128"
@@ -307,3 +327,54 @@ fn MyF() {
// CHECK:STDOUT: !9 = !{}
// CHECK:STDOUT: !10 = !DILocation(line: 8, column: 3, scope: !7)
// CHECK:STDOUT: !11 = !DILocation(line: 6, column: 1, scope: !7)
// CHECK:STDOUT: ; ModuleID = 'call_with_default_args.carbon'
// CHECK:STDOUT: source_filename = "call_with_default_args.carbon"
// CHECK:STDOUT: target datalayout = "e-m:e-p270:32:32-p271:32:32-p272:64:64-i64:64-i128:128-f80:128-n8:16:32:64-S128"
// CHECK:STDOUT: target triple = "x86_64-unknown-linux-gnu"
// CHECK:STDOUT:
// CHECK:STDOUT: define void @_CMyF.Main() !dbg !7 {
// CHECK:STDOUT: entry:
// CHECK:STDOUT: call void @_Z1Fii.carbon_thunk0(), !dbg !10
// CHECK:STDOUT: call void @_Z1Fii.carbon_thunk1(i32 3), !dbg !11
// CHECK:STDOUT: call void @_Z1Fii(i32 3, i32 4), !dbg !12
// CHECK:STDOUT: ret void, !dbg !13
// CHECK:STDOUT: }
// CHECK:STDOUT:
// CHECK:STDOUT: declare void @_Z1Fii(i32, i32)
// CHECK:STDOUT:
// CHECK:STDOUT: ; Function Attrs: alwaysinline mustprogress
// CHECK:STDOUT: define dso_local void @_Z1Fii.carbon_thunk0() #0 {
// CHECK:STDOUT: entry:
// CHECK:STDOUT: call void @_Z1Fii(i32 1, i32 2)
// CHECK:STDOUT: ret void
// CHECK:STDOUT: }
// CHECK:STDOUT:
// CHECK:STDOUT: ; Function Attrs: alwaysinline mustprogress
// CHECK:STDOUT: define dso_local void @_Z1Fii.carbon_thunk1(i32 %a) #0 {
// CHECK:STDOUT: entry:
// CHECK:STDOUT: %a.addr = alloca i32, align 4
// CHECK:STDOUT: store i32 %a, ptr %a.addr, align 4
// CHECK:STDOUT: %0 = load i32, ptr %a.addr, align 4
// CHECK:STDOUT: call void @_Z1Fii(i32 %0, i32 2)
// CHECK:STDOUT: ret void
// CHECK:STDOUT: }
// CHECK:STDOUT:
// CHECK:STDOUT: attributes #0 = { alwaysinline mustprogress "min-legal-vector-width"="0" "no-trapping-math"="true" "stack-protector-buffer-size"="0" "target-cpu"="x86-64" "target-features"="+cmov,+cx8,+fxsr,+mmx,+sse,+sse2,+x87" "tune-cpu"="generic" }
// CHECK:STDOUT:
// CHECK:STDOUT: !llvm.module.flags = !{!0, !1, !2, !3, !4}
// CHECK:STDOUT: !llvm.dbg.cu = !{!5}
// CHECK:STDOUT:
// CHECK:STDOUT: !0 = !{i32 7, !"Dwarf Version", i32 5}
// CHECK:STDOUT: !1 = !{i32 2, !"Debug Info Version", i32 3}
// CHECK:STDOUT: !2 = !{i32 1, !"wchar_size", i32 4}
// CHECK:STDOUT: !3 = !{i32 8, !"PIC Level", i32 0}
// CHECK:STDOUT: !4 = !{i32 7, !"PIE Level", i32 2}
// CHECK:STDOUT: !5 = distinct !DICompileUnit(language: DW_LANG_C, file: !6, producer: "carbon", isOptimized: false, runtimeVersion: 0, emissionKind: FullDebug)
// CHECK:STDOUT: !6 = !DIFile(filename: "call_with_default_args.carbon", directory: "")
// CHECK:STDOUT: !7 = distinct !DISubprogram(name: "MyF", linkageName: "_CMyF.Main", scope: null, file: !6, line: 6, type: !8, spFlags: DISPFlagDefinition, unit: !5)
// CHECK:STDOUT: !8 = !DISubroutineType(types: !9)
// CHECK:STDOUT: !9 = !{}
// CHECK:STDOUT: !10 = !DILocation(line: 7, column: 3, scope: !7)
// CHECK:STDOUT: !11 = !DILocation(line: 8, column: 3, scope: !7)
// CHECK:STDOUT: !12 = !DILocation(line: 9, column: 3, scope: !7)
// CHECK:STDOUT: !13 = !DILocation(line: 6, column: 1, scope: !7)