[Issue 19078] New: dmd does not remove inlined functions

[d-bugmail at puremagic.com]

https://issues.dlang.org/show_bug.cgi?id=19078

          Issue ID: 19078
           Summary: dmd does not remove inlined functions
           Product: D
           Version: D2
          Hardware: x86_64
                OS: Linux
            Status: NEW
          Severity: enhancement
          Priority: P2
         Component: dmd
          Assignee: nobody at puremagic.com
          Reporter: johnnymarler at gmail.com

I've attempted to create a minimal example to demonstrate that dmd fails to
remove inlined functions from the final executable.  In order to keep the final
executable small enough analyze with a disassembler, I've omitted
druntime/phobos.  Because of this, the example is very platform specific.  It
was made to work on the linux x86_64 platform.

--- build.sh
dmd -c -conf= -O -release -inline -betterC main.d object.d
ld -o main main.o object.o

--- object.d
module object;

alias size_t = ulong;
alias ptrdiff_t = long;

alias string = immutable(char)[];

--- main.d
pragma(inline)
int removeme(int x)
{
    return x;
}

extern(C) int main(int argc, char*[] argv, char*[] envp)
{
    sys_write(1, "running...\n".ptr, 11);
    return removeme(0);
}

extern (C) ptrdiff_t sys_exit(int exitCode)
{
    asm
    {
        naked;
        mov EAX, 60;
    }
}
extern (C) ptrdiff_t sys_write(int fd, const(char)* buf, size_t n)
{
    asm
    {
        naked;
        mov EAX, 1;
        syscall;
        ret;
    }
}
extern (C) void _start()
{
    asm
    {
        naked;
        xor RBP,RBP;
        pop RDI;
        mov RSI,RSP;
        mov RDX,RDI;
        add RDX,1;
        shl RDX, 3;
        add RDX,RSP;
        add RSP,-8;
        and RSP, 0xFFFFFFFFFFFFFFF8;
        call main;
        mov RDI, RAX;  // syscall param 1 = RAX (return value of main)
        mov RAX, 60;   // SYS_exit
        syscall;
    }
}


After running `./build.sh`, it should create the `main` executable.  You can
run it with `./main` and verify it prints "running'.  However, if you
disassemble it then you'll find that it does not remove the "removeme" function
that should have been inlined.

> objdump -d main

main:     file format elf64-x86-64


Disassembly of section .text:

00000000004000b0 <_D4main8removemeFiZi>:
  4000b0:       50                      push   %rax
  4000b1:       48 89 f8                mov    %rdi,%rax
  4000b4:       59                      pop    %rcx
  4000b5:       c3                      retq   
        ...

00000000004000b8 <main>:
  4000b8:       55                      push   %rbp
  4000b9:       48 8b ec                mov    %rsp,%rbp
  4000bc:       ba 0b 00 00 00          mov    $0xb,%edx
  4000c1:       be 10 01 40 00          mov    $0x400110,%esi
  4000c6:       bf 01 00 00 00          mov    $0x1,%edi
  4000cb:       e8 0c 00 00 00          callq  4000dc <sys_write>
  4000d0:       31 c0                   xor    %eax,%eax
  4000d2:       5d                      pop    %rbp
  4000d3:       c3                      retq   

00000000004000d4 <sys_exit>:
  4000d4:       b8 3c 00 00 00          mov    $0x3c,%eax
  4000d9:       00 00                   add    %al,(%rax)
        ...

00000000004000dc <sys_write>:
  4000dc:       b8 01 00 00 00          mov    $0x1,%eax
  4000e1:       0f 05                   syscall 
  4000e3:       c3                      retq   

00000000004000e4 <_start>:
  4000e4:       31 ed                   xor    %ebp,%ebp
  4000e6:       5f                      pop    %rdi
  4000e7:       48 89 e6                mov    %rsp,%rsi
  4000ea:       48 89 fa                mov    %rdi,%rdx
  4000ed:       48 83 c2 01             add    $0x1,%rdx
  4000f1:       48 c1 e2 03             shl    $0x3,%rdx
  4000f5:       48 01 e2                add    %rsp,%rdx
  4000f8:       48 83 c4 f8             add    $0xfffffffffffffff8,%rsp
  4000fc:       48 83 e4 f8             and    $0xfffffffffffffff8,%rsp
  400100:       e8 b3 ff ff ff          callq  4000b8 <main>
  400105:       48 89 c7                mov    %rax,%rdi
  400108:       b8 3c 00 00 00          mov    $0x3c,%eax
  40010d:       0f 05                   syscall

--