[llvm-bugs] [Bug 47530] New: clang asm chooses poorly for "=rm"
via llvm-bugs
llvm-bugs at lists.llvm.org
Mon Sep 14 14:55:11 PDT 2020
https://bugs.llvm.org/show_bug.cgi?id=47530
Bug ID: 47530
Summary: clang asm chooses poorly for "=rm"
Product: clang
Version: trunk
Hardware: PC
OS: Linux
Status: NEW
Severity: enhancement
Priority: P
Component: LLVM Codegen
Assignee: unassignedclangbugs at nondot.org
Reporter: luto at mit.edu
CC: llvm-bugs at lists.llvm.org, neeilans at live.com,
richard-llvm at metafoo.co.uk
With this trivial input:
unsigned long mov_zero(void)
{
unsigned long ret;
asm ("movq $0, %0" : "=rm" (ret));
return ret;
}
clang -O2 generates this very suboptimal output:
mov_zero:
movq $0x0,-0x8(%rsp)
mov -0x8(%rsp),%rax
ret
gcc does much better:
mov_zero:
mov $0x0,%rax
retq
--
You are receiving this mail because:
You are on the CC list for the bug.
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.llvm.org/pipermail/llvm-bugs/attachments/20200914/765d1ee4/attachment.html>
More information about the llvm-bugs
mailing list