https://bugs.llvm.org/show_bug.cgi?id=33770
Bug ID: 33770
Summary: Inline Assembler Comments
Product: new-bugs
Version: 4.0
Hardware: PC
OS: Linux
Status: NEW
Severity: enhancement
Priority: P
Component: new bugs
Assignee: unassignedb...@nondot.org
Reporter: rigger.man...@gmail.com
CC: llvm-bugs@lists.llvm.org
I'm investigating how inline assembly is used in C projects. While doing so, I
found that a number of projects include comments as part of their inline
assembly snippets. The code snippet below is an example:
#include <stdint.h>
uint64_t atomic_swap_long(volatile uint64_t *p, uint64_t v) {
__asm __volatile(
"xchgq %1,%0; # atomic_swap_long"
: "+r" (v), /* 0 */
"+m" (*p)); /* 1 */
return v;
}
When compiling with GCC (gcc -O1 -S) the following code is produced for the
inline assembly snippet on my system:
#APP
# 4 "inline-assembly-comment.c" 1
xchgq (%rdi),%rax; # atomic_swap_long
# 0 "" 2
#NO_APP
With Clang 3.8 and below, an empty line is inserted instead of the comment:
#APP
xchgq %rsi, (%rdi)
#NO_APP
With Clang 3.9 and 4.0, the newline disappeared but the comment is still not
part of the assembly code.
The comment is retained on the LLVM IR level:
%5 = call i64 asm sideeffect "xchgq\09$1,$0; # atomic_swap_long",
"=r,=*m,0,*m,~{dirflag},~{fpsr},~{flags}"(i64* %4, i64 %3, i64* %4)
On the mailing list (see
http://lists.llvm.org/pipermail/cfe-dev/2017-July/054657.html), I got the
advice to delete the trailing semicolon. This works for Clang 4.0.
--
You are receiving this mail because:
You are on the CC list for the bug._______________________________________________
llvm-bugs mailing list
llvm-bugs@lists.llvm.org
http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-bugs
