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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/114688] New: repeat load argument of an inline
 function
Date: Thu, 11 Apr 2024 06:56:45 +0000
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X-Bugzilla-Component: rtl-optimization
X-Bugzilla-Version: 13.2.0
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D114688

            Bug ID: 114688
           Summary: repeat load argument of an inline function
           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, here's the case, regression from gcc-10, x86-64
```
char g;
int v;

void foo(char p_17);
void func_1() { foo(g); }

void foo(char c) {=20
    v =3D (char)(2 - c) & c;=20
}
```

-O2 produce this for `func_1`:

```
<func_1>:
foo():
  401130:       mov    $0x2,%eax
  401135:       sub    0x2ef5(%rip),%al        # 404030 <g>
  40113b:       and    0x2eef(%rip),%al        # 404030 <g>
  401141:       movsbl %al,%eax
  401144:       mov    %eax,0x2ee2(%rip)        # 40402c <v>
func_1():
  40114a:       retq
```
it seems register allocator feels it's better to repeat load `g` instead of
generating an extra `mov` to load it.

while clang-trunk choose to do so: https://godbolt.org/z/bqxz8fMYn=