[clang][modules] Virtual function with dependent return type included and imported causes compiler to hang

[davidstone]

Given the following three files:

h.hpp:

template<typename>
struct r {
};

template<typename T>
struct s {
	virtual r<T> v() {
		return {};
	}
};

void f() {
	s<void> x;
}

a.cpp:

module;

#include "h.hpp"

export module a;

b.cpp:

#include "h.hpp"

import a;

after compiling clang++ -std=c++20 -x c++-module --precompile a.cpp -o a.pcm, the command clang++ -std=c++20 -fmodule-file=a=a.pcm -c b.cpp never completes.

This was introduced in one of

91cdd35 [clang] Improve nested name specifier AST representation (#147835)
160f5ca [AVR][NFC] Split AVRTargetTransformInfo.h to AVRTargetTransformInfo.cpp (#152841)
10e146a [AMDGPU] Fix out of bound physreg tuple condition. NFC. (#152777)
2f8e4f8 [LoongArch] Pre-commit tests for shuffle visiting same lane. NFC
b9fef09 [clang][bytecode] Add canClassify() helper (#152755)
723de7f [LV][RISCV] Try fixing Windows buildbot failure in force-vect-msg.ll. NFC
f89306f [AVR] Fix build break with shared libraries
7a6c981 [clang][bytecode] Add AccessFlags to Block (#152590)
e98b8cb [MIRParser] Remove an unnecessary cast (NFC) (#152835)
39941a2 [ExecutionEngine] Remove an unnecessary cast (NFC) (#152836)
5ebb22d [Mips] Remove an unnecessary cast (NFC) (#152837)
190ad0b [llvm] Proofread SourceLevelDebugging.rst (#152838)
d1827f0 Add REQUIRES: riscv to test added in 151639 to skip the test when riscv is not built. (#152858)
92a966b [RISCV] Add -march=unset to cancel and ignore a previous -march. (#148321)
7fb8630 [RISCV] Add another packh+packw pattern. (#152744)
e86c9b6 [libc][math] Refactor cos implementation to header-only in src/__support/math folder. (#151883)
870aa97 [clang][bytecode] Use visitExpr() in interpretCall (#152857)
24b7727 [libc++] Implement LWG4222 'expected' constructor from a single value missing a constraint (#152676)
62735d2 [DAGCombine] Correctly extend the constant RHS in TargetLowering::SimplifySetCC (#152862)
aee4f2b [libFuzzer] always install signal handler with SA_ONSTACK (#147422)
06fd0f9 [VPlan] Move initial skeleton construction earlier (NFC). (#150848)
dea50a1 [flang][Driver] Enable FLANG_DEFAULT_LINKER (#149786)
d9199a8 [LV] Add missing check lines for tests.
c9b6242 [CIR] Fix build after the improved nested name specifier AST repr (91cdd35)
34164da [clang] missing changes to the Rewriter (#152845)

git bisect cannot reduce it any further because most of those commits fail to compile. I suspect the culprit is 91cdd35 @mizvekov based solely on "539 files changed +11195 -10586 lines changed". The first commit that successfully compiles and causes the hang is 34164da.

[davidstone]

Note that this pattern appears in <format>, so it essentially cannot be used with modules currently.

[llvmbot]

@llvm/issue-subscribers-clang-modules

Author: David Stone (davidstone)

Given the following three files:

h.hpp:

template<typename>
struct r {
};

template<typename T>
struct s {
	virtual r<T> v() {
		return {};
	}
};

void f() {
	s<void> x;
}

a.cpp:

module;

#include "h.hpp"

export module a;

b.cpp:

#include "h.hpp"

import a;

after compiling clang++ -std=c++20 -x c++-module --precompile a.cpp -o a.pcm, the command clang++ -std=c++20 -fmodule-file=a=a.pcm -c b.cpp never completes.

This was introduced in one of

91cdd35 [clang] Improve nested name specifier AST representation (#147835)
160f5ca [AVR][NFC] Split AVRTargetTransformInfo.h to AVRTargetTransformInfo.cpp (#152841)
10e146a [AMDGPU] Fix out of bound physreg tuple condition. NFC. (#152777)
2f8e4f8 [LoongArch] Pre-commit tests for shuffle visiting same lane. NFC
b9fef09 [clang][bytecode] Add canClassify() helper (#152755)
723de7f [LV][RISCV] Try fixing Windows buildbot failure in force-vect-msg.ll. NFC
f89306f [AVR] Fix build break with shared libraries
7a6c981 [clang][bytecode] Add AccessFlags to Block (#152590)
e98b8cb [MIRParser] Remove an unnecessary cast (NFC) (#152835)
39941a2 [ExecutionEngine] Remove an unnecessary cast (NFC) (#152836)
5ebb22d [Mips] Remove an unnecessary cast (NFC) (#152837)
190ad0b [llvm] Proofread SourceLevelDebugging.rst (#152838)
d1827f0 Add REQUIRES: riscv to test added in 151639 to skip the test when riscv is not built. (#152858)
92a966b [RISCV] Add -march=unset to cancel and ignore a previous -march. (#148321)
7fb8630 [RISCV] Add another packh+packw pattern. (#152744)
e86c9b6 [libc][math] Refactor cos implementation to header-only in src/__support/math folder. (#151883)
870aa97 [clang][bytecode] Use visitExpr() in interpretCall (#152857)
24b7727 [libc++] Implement LWG4222 'expected' constructor from a single value missing a constraint (#152676)
62735d2 [DAGCombine] Correctly extend the constant RHS in TargetLowering::SimplifySetCC (#152862)
aee4f2b [libFuzzer] always install signal handler with SA_ONSTACK (#147422)
06fd0f9 [VPlan] Move initial skeleton construction earlier (NFC). (#150848)
dea50a1 [flang][Driver] Enable FLANG_DEFAULT_LINKER (#149786)
d9199a8 [LV] Add missing check lines for tests.
c9b6242 [CIR] Fix build after the improved nested name specifier AST repr (91cdd35)
34164da [clang] missing changes to the Rewriter (#152845)

git bisect cannot reduce it any further because most of those commits fail to compile. I suspect the culprit is 91cdd35 @mizvekov based solely on "539 files changed +11195 -10586 lines changed". The first commit that successfully compiles and causes the hang is 34164da.