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From: "hjl.tools at gmail dot com" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug target/63527] New: [5 Regression] -fPIC generates more instructions
Date: Mon, 13 Oct 2014 18:49:00 -0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=63527

            Bug ID: 63527
           Summary: [5 Regression] -fPIC generates more instructions
           Product: gcc
           Version: 5.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: target
          Assignee: unassigned at gcc dot gnu.org
          Reporter: hjl.tools at gmail dot com
                CC: evstupac at gmail dot com
            Target: i686-linux

On Linux/x86, r216154 generates more instructions with -O2 -fPIC
for

----
struct cache_file
{
  char magic[sizeof "ld.so-1.7.0" - 1];
  unsigned int nlibs;
};
typedef unsigned int size_t;
size_t cachesize __attribute__ ((visibility ("hidden")));
struct cache_file *cache __attribute__ ((visibility ("hidden")));
extern int __munmap (void *__addr, size_t __len);
void
_dl_unload_cache (void)
{
  if (cache != ((void *)0) && cache != (struct cache_file *) -1)
    {
      __munmap (cache, cachesize);
      cache = ((void *)0) ;
    }
}
----

r216153 generates

---
    .text
.LHOTB0:
    .p2align 4,,15
    .globl    _dl_unload_cache
    .type    _dl_unload_cache, @function
_dl_unload_cache:
    pushl    %ebx
    call    __x86.get_pc_thunk.bx
    addl    $_GLOBAL_OFFSET_TABLE_, %ebx
    subl    $8, %esp
    movl    cache@GOTOFF(%ebx), %eax
    leal    -1(%eax), %edx
    cmpl    $-3, %edx
    ja    .L1
    subl    $8, %esp
    pushl    cachesize@GOTOFF(%ebx)
    pushl    %eax
    call    __munmap@PLT
    movl    $0, cache@GOTOFF(%ebx)
    addl    $16, %esp
.L1:
    addl    $8, %esp
    popl    %ebx
    ret
    .size    _dl_unload_cache, .-_dl_unload_cache
    .section    .text.unlikely
.LCOLDE0:
    .text
.LHOTE0:
    .hidden    cache
    .comm    cache,4,4
    .hidden    cachesize
    .comm    cachesize,4,4
    .section   
.text.__x86.get_pc_thunk.bx,"axG",@progbits,__x86.get_pc_thunk.bx,comdat
    .globl    __x86.get_pc_thunk.bx
    .hidden    __x86.get_pc_thunk.bx
    .type    __x86.get_pc_thunk.bx, @function
__x86.get_pc_thunk.bx:
    movl    (%esp), %ebx
    ret
---

r216154 generates

--
    .text
.LHOTB0:
    .p2align 4,,15
    .globl    _dl_unload_cache
    .type    _dl_unload_cache, @function
_dl_unload_cache:
    pushl    %esi
    pushl    %ebx
    call    __x86.get_pc_thunk.si
    addl    $_GLOBAL_OFFSET_TABLE_, %esi
    subl    $4, %esp
    movl    cache@GOTOFF(%esi), %eax
    leal    -1(%eax), %edx
    cmpl    $-3, %edx
    ja    .L1
    subl    $8, %esp
    pushl    cachesize@GOTOFF(%esi)
    movl    %esi, %ebx
    pushl    %eax
    call    __munmap@PLT
    movl    $0, cache@GOTOFF(%esi)
    addl    $16, %esp
.L1:
    addl    $4, %esp
    popl    %ebx
    popl    %esi
    ret
    .size    _dl_unload_cache, .-_dl_unload_cache
    .section    .text.unlikely
.LCOLDE0:
    .text
.LHOTE0:
    .hidden    cache
    .comm    cache,4,4
    .hidden    cachesize
    .comm    cachesize,4,4
    .section   
.text.__x86.get_pc_thunk.si,"axG",@progbits,__x86.get_pc_thunk.si,comdat
    .globl    __x86.get_pc_thunk.si
    .hidden    __x86.get_pc_thunk.si
    .type    __x86.get_pc_thunk.si, @function
__x86.get_pc_thunk.si:
    movl    (%esp), %esi
    ret
--

Why doesn't r216154 simply use %ebx to access cache, cachesize
and __munmap?