[Bug c/40072] New: Nonoptimal code - CMOVxx %eax,%edi; mov %edi,%eax; retq

[vvv at ru dot ru]

Sometimes GCC generate code at end of function:

 cmovge %eax,%edi
 mov    %edi,%eax
 retq   

but faster:

 cmovl %edi,%eax
 retq   

Example:

# cat test.c

#define MX 0
#define LIM 7

char char_char(char m)
{if(m>LIM) return(MX); return(m);}

char char_int(int m)
{if(m>LIM) return(MX); return(m);}

char char_uint(unsigned int m)
{if(m>LIM) return(MX); return(m);}

char char_long(long m)
{if(m>LIM) return(MX); return(m);}

char char_ulong(unsigned long m)
{if(m>LIM) return(MX); return(m);}


int int_char(char m)
{if(m>LIM) return(MX); return(m);}

int int_int(int m)
{if(m>LIM) return(MX); return(m);}      // Nonoptimal 
int int_uint(unsigned int m)
{if(m>LIM) return(MX); return(m);}

int int_long(long m)
{if(m>LIM) return(MX); return(m);}

int int_ulong(unsigned long m)
{if(m>LIM) return(MX); return(m);}



unsigned int uint_char(char m)
{if(m>LIM) return(MX); return(m);}

unsigned int uint_int(int m)
{if(m>LIM) return(MX); return(m);}

unsigned int uint_uint(unsigned int m)  //Nonoptimal
{if(m>LIM) return(MX); return(m);}

unsigned int uint_long(long m)
{if(m>LIM) return(MX); return(m);}

unsigned int uint_ulong(unsigned long m)
{if(m>LIM) return(MX); return(m);}



long long_char(char m)
{if(m>LIM) return(MX); return(m);}

long long_int(int m)
{if(m>LIM) return(MX); return(m);}

long long_uint(unsigned int m)
{if(m>LIM) return(MX); return(m);}

long long_long(long m)                  //Nonoptimal
{if(m>LIM) return(MX); return(m);}

long long_ulong(unsigned long m)
{if(m>LIM) return(MX); return(m);}




unsigned long ulong_char(char m)
{if(m>LIM) return(MX); return(m);}

unsigned long ulong_int(int m)
{if(m>LIM) return(MX); return(m);}

unsigned long ulong_uint(unsigned int m)
{if(m>LIM) return(MX); return(m);}

unsigned long ulong_long(long m)
{if(m>LIM) return(MX); return(m);}

unsigned long ulong_ulong(unsigned long m)      //Nonoptimal
{if(m>LIM) return(MX); return(m);}

# gcc -o t test.c -O2 -c
# objdump -d t

t:     file format elf64-x86-64


Disassembly of section .text:

0000000000000000 <char_char>:
   0:   89 f8                   mov    %edi,%eax
   2:   40 80 ff 08             cmp    $0x8,%dil
   6:   ba 00 00 00 00          mov    $0x0,%edx
   b:   0f 4d c2                cmovge %edx,%eax    <--- It's ok! Optimal
   e:   c3                      retq   
   f:   90                      nop    

<skip...>

0000000000000060 <int_int>:
  60:   83 ff 08                cmp    $0x8,%edi
  63:   b8 00 00 00 00          mov    $0x0,%eax
  68:   0f 4d f8                cmovge %eax,%edi    <--- Nonoptimal
  6b:   89 f8                   mov    %edi,%eax    <--- Nonoptimal
  6d:   c3                      retq   
  6e:   66 90                   xchg   %ax,%ax

<skip...>

00000000000000c0 <uint_uint>:
  c0:   83 ff 08                cmp    $0x8,%edi
  c3:   b8 00 00 00 00          mov    $0x0,%eax
  c8:   0f 43 f8                cmovae %eax,%edi    <--- Nonoptimal
  cb:   89 f8                   mov    %edi,%eax    <--- Nonoptimal
  cd:   c3                      retq   
  ce:   66 90                   xchg   %ax,%ax

<skip...>

0000000000000120 <long_long>:
 120:   48 83 ff 08             cmp    $0x8,%rdi
 124:   b8 00 00 00 00          mov    $0x0,%eax
 129:   48 0f 4d f8             cmovge %rax,%rdi    <--- Nonoptimal
 12d:   48 89 f8                mov    %rdi,%rax    <--- Nonoptimal
 130:   c3                      retq   

<skip...>

0000000000000190 <ulong_ulong>:
 190:   48 83 ff 08             cmp    $0x8,%rdi
 194:   b8 00 00 00 00          mov    $0x0,%eax
 199:   48 0f 43 f8             cmovae %rax,%rdi    <--- Nonoptimal
 19d:   48 89 f8                mov    %rdi,%rax    <--- Nonoptimal
 1a0:   c3                      retq


-- 
           Summary: Nonoptimal code -  CMOVxx %eax,%edi; mov    %edi,%eax;
                    retq
           Product: gcc
           Version: 4.4.0
            Status: UNCONFIRMED
          Severity: minor
          Priority: P3
         Component: c
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: vvv at ru dot ru


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=40072