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From: "absoler at smail dot nju.edu.cn" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug rtl-optimization/114591] New: rtl-reload introduce an extra
 load operation since gcc-12
Date: Thu, 04 Apr 2024 18:57:39 +0000
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X-Bugzilla-Product: gcc
X-Bugzilla-Component: rtl-optimization
X-Bugzilla-Version: 13.2.0
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D114591

            Bug ID: 114591
           Summary: rtl-reload introduce an extra load operation since
                    gcc-12
           Product: gcc
           Version: 13.2.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: rtl-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: absoler at smail dot nju.edu.cn
  Target Milestone: ---

Hi, I found such a case:
```
unsigned v1;
long long v2;

short func_1() {
    v2 =3D v1;
    return v2;
}
```
gcc-12 and gcc-13 would produce under -O2:
```
func_1:
 mov    0x0(%rip),%eax        # v1
 mov    %rax,0x0(%rip)        # v2
 movzwl 0x0(%rip),%eax        # v1

```
and gcc-11's:

```
func_1:
 mov    0x0(%rip),%edx        # v1
 mov    %rdx,0x0(%rip)        # v2
 mov    %rdx,%rax
```

I guess the latter is better? the second load of `v1` was introduced in
RTL-reload pass, maybe this pessimize the performance.=