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Subject: [Bug middle-end/47735] New: [4.5/4.6 Regression] Unnecessary adjustments to stack pointer
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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=47735

           Summary: [4.5/4.6 Regression] Unnecessary adjustments to stack
                    pointer
           Product: gcc
           Version: 4.6.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: middle-end
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: hjl.tools@gmail.com
                CC: matz@gcc.gnu.org


For this tescase, gcc 4.4 generates the most efficient code
while 4.5/4.6 become worse and worse:

[hjl@gnu-6 gcc]$ cat x.i 
unsigned mulh(unsigned a, unsigned b)
{
  unsigned long long l __attribute__ ((aligned(32)))
    =((unsigned long long)a * (unsigned long long)b) >> 32;
  return l;
}
[hjl@gnu-6 gcc]$ /usr/gcc-4.4/bin/gcc -O2 -S -fomit-frame-pointer x.i -m32
[hjl@gnu-6 gcc]$ cat x.s 
    .file    "x.i"
    .text
    .p2align 4,,15
.globl mulh
    .type    mulh, @function
mulh:
    movl    8(%esp), %eax
    mull    4(%esp)
    movl    %edx, %eax
    ret
    .size    mulh, .-mulh
    .ident    "GCC: (GNU) 4.4.4"
    .section    .note.GNU-stack,"",@progbits
[hjl@gnu-6 gcc]$ /usr/gcc-4.5/bin/gcc -O2 -S -fomit-frame-pointer x.i -m32
[hjl@gnu-6 gcc]$ cat x.s
    .file    "x.i"
    .text
    .p2align 4,,15
.globl mulh
    .type    mulh, @function
mulh:
    pushl    %ebp
    movl    %esp, %ebp
    movl    12(%ebp), %eax
    mull    8(%ebp)
    popl    %ebp
    movl    %edx, %eax
    ret
    .size    mulh, .-mulh
    .ident    "GCC: (GNU) 4.5.1 20100507 (prerelease) [gcc-4_5-branch revision
159167]"
    .section    .note.GNU-stack,"",@progbits
[hjl@gnu-6 gcc]$ ./xgcc -B./  -O2 -S -fomit-frame-pointer x.i -m32
[hjl@gnu-6 gcc]$ cat x.s
    .file    "x.i"
    .text
    .p2align 4,,15
    .globl    mulh
    .type    mulh, @function
mulh:
.LFB0:
    .cfi_startproc
    pushl    %ebp
    .cfi_def_cfa_offset 8
    .cfi_offset 5, -8
    movl    %esp, %ebp
    .cfi_def_cfa_register 5
    andl    $-32, %esp
    movl    12(%ebp), %eax
    mull    8(%ebp)
    leave
    .cfi_restore 5
    .cfi_def_cfa 4, 4
    movl    %edx, %eax
    ret
    .cfi_endproc
.LFE0:
    .size    mulh, .-mulh
    .ident    "GCC: (GNU) 4.6.0 20110131 (experimental)"
    .section    .note.GNU-stack,"",@progbits
[hjl@gnu-6 gcc]$

This is caused by revision 146817:

http://gcc.gnu.org/ml/gcc-cvs/2009-04/msg01459.html