[llvm-bugs] [Bug 51255] New: tail call applied to __attribute__((no_caller_saved_registers)) negates its purpose

[via llvm-bugs]

https://bugs.llvm.org/show_bug.cgi?id=51255

            Bug ID: 51255
           Summary: tail call applied to
                    __attribute__((no_caller_saved_registers)) negates its
                    purpose
           Product: clang
           Version: 12.0
          Hardware: PC
                OS: Linux
            Status: NEW
          Severity: normal
          Priority: P
         Component: -New Bugs
          Assignee: unassignedclangbugs at nondot.org
          Reporter: thiago at kde.org
                CC: htmldeveloper at gmail.com, llvm-bugs at lists.llvm.org,
                    neeilans at live.com, richard-llvm at metafoo.co.uk

$ clang --version
clang version 12.0.1
Target: x86_64-unknown-linux-gnu
Thread model: posix
InstalledDir: /usr/bin

$ cat test.c
// general-regs-only is helpful with Clang trunk
__attribute__((target("general-regs-only"), no_caller_saved_registers))
int g(int (*f)(void))
{
    return f();
}

$ clang -O2 -S -o - -mgeneral-regs-only test.c
[ see result with clang trunk at https://clang.godbolt.org/z/rMzaPjhn3 ]
g(int (*)()):                              # @g(int (*)())
        pushq   %r11
        pushq   %r10
        pushq   %r9
        pushq   %r8
        pushq   %rsi
        pushq   %rdx
        pushq   %rcx
        pushq   %rax
        popq    %rax
        popq    %rcx
        popq    %rdx
        popq    %rsi
        popq    %r8
        popq    %r9
        popq    %r10
        popq    %r11
        jmpq    *%rdi                           # TAILCALL

The register preservation does not encompass the actual function call.

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