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From: "miguel.ojeda.sandonis at gmail dot com" <gcc-bugzilla@gcc.gnu.org>
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Subject: [Bug tree-optimization/97856] New: Missed optimization: repeated call
Date: Mon, 16 Nov 2020 17:40:55 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D97856

            Bug ID: 97856
           Summary: Missed optimization: repeated call
           Product: gcc
           Version: unknown
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: miguel.ojeda.sandonis at gmail dot com
  Target Milestone: ---

For code such as:

    void f(int);
    void g(int v) {
        switch (v) {
            case 1: f(1);
            case 2: f(2);
            case 3: f(3);
            default: f(4);
        }
    }

GCC generates for e.g. x86_64:

    g(int):
            subq    $8, %rsp
            cmpl    $2, %edi
            je      .L2
            cmpl    $3, %edi
            je      .L3
            cmpl    $1, %edi
            je      .L13
            movl    $4, %edi
            addq    $8, %rsp
            jmp     f(int)
    .L13:
            call    f(int)
    .L2:
            movl    $2, %edi
            call    f(int)
    .L3:
            movl    $3, %edi
            call    f(int)
            movl    $4, %edi
            addq    $8, %rsp
            jmp     f(int)

Repeating the `f(4);` call can be avoided by reordering the cases, reducing
code size.=