https://llvm.org/bugs/show_bug.cgi?id=28660
Bug ID: 28660
Summary: mcount inlining bug when -pg and -O2 enabled
Product: clang
Version: trunk
Hardware: PC
OS: Linux
Status: NEW
Severity: normal
Priority: P
Component: LLVM Codegen
Assignee: unassignedclangb...@nondot.org
Reporter: hong.gyu....@lge.com
CC: llvm-bugs@lists.llvm.org
Classification: Unclassified
See the simple example below.
$ cat mcount-test.c
int bar()
{
return 0;
}
int foo()
{
return bar();
}
int main()
{
return foo();
}
If the example is compiled with -pg and -O2 options. It generates the code as
below:
$ clang -pg -O2 -S mcount-test.c
$ cat mcount-test.s
(shows assembly code only ...)
bar:
pushq %rbp
movq %rsp, %rbp
callq mcount
xorl %eax, %eax
popq %rbp
retq
foo:
pushq %rbp
movq %rsp, %rbp
callq mcount
callq mcount @ (1) calling bar is inlined with mcount
xorl %eax, %eax
popq %rbp
retq
main:
pushq %rbp
movq %rsp, %rbp
callq mcount
callq mcount @ (2) calling foo is inlined with mcount
callq mcount @ (3) calling bar is inlined with mcount
xorl %eax, %eax
popq %rbp
retq
As I put some comments, the problem is that function inlining is done with
mcount call.
bar() has a single mcount at the entry of function, but foo() has two mcount
calls. It's because bar is inlined with its mcount call into foo's body. And
also main() has three mcount calls because the foo() is inlined its own mcount
and its body that has two mcount calls inside.
This is tested on the current trunk.
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