https://gcc.gnu.org/bugzilla/show_bug.cgi?id=78936
Bug ID: 78936
Summary: Interprocedural constant propagation miscompiles C++
methods on i686 Windows
Product: gcc
Version: unknown
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: target
Assignee: unassigned at gcc dot gnu.org
Reporter: rnk at google dot com
Target Milestone: ---
The following test case has an issue where some interprocedural optimziation in
GCC 6.2.0 appears to have mixed up the calling convention of a C++ thiscall
method:
https://drive.google.com/open?id=0B5-KodWdXF4YZ1pVczVQX0tiOGM
When I compile the linked file like so, I get the following assembly snippets,
which seem to corrupt the stack pointer:
$ g++ -O2 llvm-subtarget-emitter.cpp -S -o t.s
$ c++filt < t.s | less
...
(anonymous namespace)::SubtargetEmitter::EmitProcessorProp(llvm::raw_ostream&,
llvm::Record const*, llvm::StringRef, char) [clone .constprop.544]:
...
addl $28, %esp
.cfi_remember_state
.cfi_def_cfa_offset 20
popl %ebx
.cfi_restore 3
.cfi_def_cfa_offset 16
popl %esi
.cfi_restore 6
.cfi_def_cfa_offset 12
popl %edi
.cfi_restore 7
.cfi_def_cfa_offset 8
popl %ebp
.cfi_restore 5
.cfi_def_cfa_offset 4
ret
.p2align 4,,10
...
(anonymous namespace)::SubtargetEmitter::EmitSchedModel(llvm::raw_ostream&):
...
call (anonymous
namespace)::SubtargetEmitter::EmitProcessorProp(llvm::raw_ostream&,
llvm::Record const*, llvm::StringRef, char) [clone .constprop.544]
movl 28(%edi), %edx
movl 8(%ebp), %eax
subl $8, %esp
movl $LC170, (%esp)
movl $17, 4(%esp)
call (anonymous
namespace)::SubtargetEmitter::EmitProcessorProp(llvm::raw_ostream&,
llvm::Record const*, llvm::StringRef, char) [clone .constprop.544]
movl 28(%edi), %edx
movl 8(%ebp), %eax
subl $8, %esp
...
Note that the "ret" instruction doesn't match the "sub $8, %esp" instructions
after the call sites of SubtargetEmitter::EmitProcessorProp. The callee-cleanup
property of the EmitProcessorProp clone seems to have been lost, or the call
site hasn't been updated to treat it as a caller cleanup call.
This issue was encountered while building LLVM with the latest GCC provided by
mingw-w64: http://lists.llvm.org/pipermail/cfe-dev/2016-December/051980.html
$ g++ --version
g++.exe (i686-posix-dwarf-rev1, Built by MinGW-W64 project) 6.2.0
Copyright (C) 2016 Free Software Foundation, Inc.
This is free software; see the source for copying conditions. There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
