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[Bug rtl-optimization/23100] New: poor code generation for i686
- From: "dann at godzilla dot ics dot uci dot edu" <gcc-bugzilla at gcc dot gnu dot org>
- To: gcc-bugs at gcc dot gnu dot org
- Date: 27 Jul 2005 19:12:36 -0000
- Subject: [Bug rtl-optimization/23100] New: poor code generation for i686
- Reply-to: gcc-bugzilla at gcc dot gnu dot org
Compiling the code below (extracted from xterm-202) with
-fno-inline -O2 -march=i686
typedef unsigned long Atom;
static int
CutBuffer(unsigned code)
{
int cutbuffer;
switch (code) {
case ((Atom) 9):
cutbuffer = 0;
break;
case ((Atom) 10):
cutbuffer = 1;
break;
case ((Atom) 11):
cutbuffer = 2;
break;
case ((Atom) 12):
cutbuffer = 3;
break;
case ((Atom) 13):
cutbuffer = 4;
break;
case ((Atom) 14):
cutbuffer = 5;
break;
case ((Atom) 15):
cutbuffer = 6;
break;
case ((Atom) 16):
cutbuffer = 7;
break;
default:
cutbuffer = -1;
break;
}
return cutbuffer;
}
int foo (unsigned code)
{
return CutBuffer (code);
}
generates:
CutBuffer:
subl $9, %eax
movl $-1, %edx
pushl %ebp
cmpl $7, %eax
movl %esp, %ebp
ja .L12
jmp *.L11(,%eax,4)
.section .rodata
.align 4
.align 4
.L11:
.long .L3
.long .L4
.long .L5
.long .L6
.long .L7
.long .L8
.long .L9
.long .L10
.text
.L9:
movl $6, %edx
.p2align 4,,15
.L12:
popl %ebp
movl %edx, %eax
ret
.L3:
popl %ebp
xorl %edx, %edx
movl %edx, %eax
.p2align 4,,2
ret
.L10:
popl %ebp
movl $7, %edx
movl %edx, %eax
ret
.L8:
popl %ebp
movl $5, %edx
movl %edx, %eax
ret
.L7:
popl %ebp
movl $4, %edx
movl %edx, %eax
ret
.L6:
popl %ebp
movl $3, %edx
movl %edx, %eax
ret
[snip]
Note the sequences: movl NUMBER, %edx
movl %edx, %eax
instead of using only one instruction for the same thing: movl NUMBER, %eax
--
Summary: poor code generation for i686
Product: gcc
Version: 4.1.0
Status: UNCONFIRMED
Severity: normal
Priority: P2
Component: rtl-optimization
AssignedTo: unassigned at gcc dot gnu dot org
ReportedBy: dann at godzilla dot ics dot uci dot edu
CC: gcc-bugs at gcc dot gnu dot org
GCC host triplet: i686-pc-linux-gnu
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=23100