[Bug rtl-optimization/13355] Suboptimal code generated with global register variables

[msebor at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=13355

Martin Sebor  changed:

   What|Removed |Added

 Status|NEW |RESOLVED
 CC||msebor at gcc dot gnu.org
 Resolution|--- |FIXED

--- Comment #12 from Martin Sebor  ---
Wiuth today's top of trunk (GCC 7.0) the object code below matches closely the
assembly expected in comment #3.  Resolving as fixed.

op_imull_EAX_T0:
.LFB1:
.cfi_startproc
movl%ebx, %eax
imull   0(%ebp)
movl%edx, %ecx
movl%eax, %edx
movl%eax, 0(%ebp)
movl%edx, %eax
cltd
xorl%eax, %eax
cmpl%ecx, %edx
setne   %al
movl%ecx, 8(%ebp)
movl%eax, 32(%ebp)
ret

[Bug rtl-optimization/13355] Suboptimal code generated with global register variables

[steven at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=13355



--- Comment #9 from Steven Bosscher steven at gcc dot gnu.org 2012-11-08 
22:41:41 UTC ---

(In reply to comment #6)

 A reduced testcase for the second case.

 On mainline, i686-pc-linux-gnu.

 

 /* -march=i686 -mtune=i686 -fomit-frame-pointer -O2 */

 

 register int ebx asm (ebx);

 register int dummy1 asm (esi);

 register int dummy2 asm (ebp);

 

 int

 foo (int arg)

 {

   long long res = (long long) arg * (long long) ebx;

   return (int) res;

 }

 

 Global variables take up three registers from IA-32!



GCC 4.1, GCC 4.3, and GCC 4.7 compile this to:

foo:

subl$12, %esp

movl16(%esp), %eax

imull   %ebx

movl%eax, (%esp)

movl(%esp), %eax

movl%edx, 4(%esp)

addl$12, %esp

ret





Trunk r193340 compiles it to:

foo:

movl%ebx, %eax

imull   4(%esp)

ret

[Bug rtl-optimization/13355] Suboptimal code generated with global register variables

[steven at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=13355



Steven Bosscher steven at gcc dot gnu.org changed:



   What|Removed |Added



 CC||steven at gcc dot gnu.org



--- Comment #10 from Steven Bosscher steven at gcc dot gnu.org 2012-11-08 
22:46:53 UTC ---

(In reply to comment #1)

 Created attachment 5301 [details]

 example .c file that shows behavior with

  gcc -march=i686 -mtune=i686 -fomit-frame-pointer -O2 test.c



GCC 4.7.1 compiles the two interesting functions in the test case to:



op_cmovl_EAX_T1_T0:

testl   %ebx, %ebx

je  .L2

movl%esi, 0(%ebp)

.L2:

ret



op_imull_EAX_T0:

subl$20, %esp

movl0(%ebp), %eax

imull   %ebx

movl%eax, (%esp)

movl%eax, 0(%ebp)

movl(%esp), %eax

movl%edx, 4(%esp)

movl%edx, 8(%ebp)

movl%eax, %edx

movl%eax, 8(%esp)

sarl$31, %edx

movl4(%esp), %eax

movl%edx, 12(%esp)

cmpl%eax, 12(%esp)

setne   %al

movzbl  %al, %eax

movl%eax, 32(%ebp)

addl$20, %esp

ret





Trunk r193340 produces the following:



op_cmovl_EAX_T1_T0:

testl   %ebx, %ebx

je  .L2

movl%esi, 0(%ebp)

.L2:

ret



op_imull_EAX_T0:

subl$12, %esp

movl%ebx, %eax

imull   0(%ebp)

movl%eax, 0(%ebp)

movl%eax, (%esp)

sarl$31, %eax

movl%eax, 4(%esp)

xorl%eax, %eax

cmpl%edx, 4(%esp)

movl%edx, 8(%ebp)

setne   %al

movl%eax, 32(%ebp)

addl$12, %esp

ret

[Bug rtl-optimization/13355] Suboptimal code generated with global register variables

[steven at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=13355



Steven Bosscher steven at gcc dot gnu.org changed:



   What|Removed |Added



 CC|steven at gcc dot gnu.org   |



--- Comment #11 from Steven Bosscher steven at gcc dot gnu.org 2012-11-08 
22:50:51 UTC ---

So, not quite the code of comment #3, but LRA does appear to improve

things quite a bit.  I'll leave it to the OP to decide whether this

bug report is resolved sufficiently well to close it.

[Bug rtl-optimization/13355] Suboptimal code generated with global register variables

[pinskia at gcc dot gnu dot org]

--- Additional Comments From pinskia at gcc dot gnu dot org  2005-03-29 
01:55 ---
Some of this is already fixed.

-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=13355