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* [Bug rtl-optimization/21643] New: GCC fails to merge ranges in comparison.
@ 2005-05-18 12:32 dwmw2 at infradead dot org
2005-05-18 12:33 ` [Bug rtl-optimization/21643] " dwmw2 at infradead dot org
` (3 more replies)
0 siblings, 4 replies; 5+ messages in thread
From: dwmw2 at infradead dot org @ 2005-05-18 12:32 UTC (permalink / raw)
To: gcc-bugs
I'd expect the result of compiling these two functions to be identical, but it
isn't:
int fish1(unsigned char c)
{
if (c =='"' || c == 0x20 || c < 0x20)
return 1;
}
int fish2(unsigned char c)
{
if (c == '"' || c <= 0x20)
return 1;
}
If I remove the 'c == '"' ||' from each, I do get the expected results.
$ gcc -O2 -S asd.c -o /dev/stdout
.file "asd.c"
.section ".text"
.align 2
.p2align 4,,15
.globl fish1
.type fish1, @function
fish1:
mr 0,3
li 3,1
cmpwi 7,0,34
cmpwi 6,0,32
beqlr 7
cmplwi 7,0,31
beqlr 6
blelr 7
blr
.size fish1,.-fish1
.align 2
.p2align 4,,15
.globl fish2
.type fish2, @function
fish2:
mr 0,3
li 3,1
cmpwi 7,0,34
cmplwi 6,0,32
beqlr 7
blelr 6
blr
.size fish2,.-fish2
.ident "GCC: (GNU) 4.0.0 20050512 (Red Hat 4.0.0-5)"
.section .note.GNU-stack,"",@progbits
--
Summary: GCC fails to merge ranges in comparison.
Product: gcc
Version: 4.0.0
Status: UNCONFIRMED
Severity: normal
Priority: P2
Component: rtl-optimization
AssignedTo: unassigned at gcc dot gnu dot org
ReportedBy: dwmw2 at infradead dot org
CC: gcc-bugs at gcc dot gnu dot org,jakub at redhat dot com
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=21643
^ permalink raw reply [flat|nested] 5+ messages in thread
* [Bug rtl-optimization/21643] GCC fails to merge ranges in comparison.
2005-05-18 12:32 [Bug rtl-optimization/21643] New: GCC fails to merge ranges in comparison dwmw2 at infradead dot org
@ 2005-05-18 12:33 ` dwmw2 at infradead dot org
2005-05-18 12:39 ` [Bug tree-optimization/21643] " pinskia at gcc dot gnu dot org
` (2 subsequent siblings)
3 siblings, 0 replies; 5+ messages in thread
From: dwmw2 at infradead dot org @ 2005-05-18 12:33 UTC (permalink / raw)
To: gcc-bugs
------- Additional Comments From dwmw2 at infradead dot org 2005-05-18 12:33 -------
Happens with gcc 3.4 too, and also on i386.
--
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=21643
^ permalink raw reply [flat|nested] 5+ messages in thread
* [Bug tree-optimization/21643] GCC fails to merge ranges in comparison.
2005-05-18 12:32 [Bug rtl-optimization/21643] New: GCC fails to merge ranges in comparison dwmw2 at infradead dot org
2005-05-18 12:33 ` [Bug rtl-optimization/21643] " dwmw2 at infradead dot org
@ 2005-05-18 12:39 ` pinskia at gcc dot gnu dot org
2005-05-18 17:21 ` trt at acm dot org
2005-05-18 17:28 ` trt at acm dot org
3 siblings, 0 replies; 5+ messages in thread
From: pinskia at gcc dot gnu dot org @ 2005-05-18 12:39 UTC (permalink / raw)
To: gcc-bugs
------- Additional Comments From pinskia at gcc dot gnu dot org 2005-05-18 12:38 -------
Confirmed.
--
What |Removed |Added
----------------------------------------------------------------------------
CC| |pinskia at gcc dot gnu dot
| |org
Severity|normal |enhancement
Status|UNCONFIRMED |NEW
Component|rtl-optimization |tree-optimization
Ever Confirmed| |1
Keywords| |missed-optimization
Last reconfirmed|0000-00-00 00:00:00 |2005-05-18 12:38:44
date| |
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=21643
^ permalink raw reply [flat|nested] 5+ messages in thread
* [Bug tree-optimization/21643] GCC fails to merge ranges in comparison.
2005-05-18 12:32 [Bug rtl-optimization/21643] New: GCC fails to merge ranges in comparison dwmw2 at infradead dot org
2005-05-18 12:33 ` [Bug rtl-optimization/21643] " dwmw2 at infradead dot org
2005-05-18 12:39 ` [Bug tree-optimization/21643] " pinskia at gcc dot gnu dot org
@ 2005-05-18 17:21 ` trt at acm dot org
2005-05-18 17:28 ` trt at acm dot org
3 siblings, 0 replies; 5+ messages in thread
From: trt at acm dot org @ 2005-05-18 17:21 UTC (permalink / raw)
To: gcc-bugs
------- Additional Comments From trt at acm dot org 2005-05-18 17:21 -------
This is because fold-const.c only does ad-hoc re-association.
Here is an example for fold_truthop (approx line 8805)
/* Check for the possibility of merging component references. If our
lhs is another similar operation, try to merge its rhs with our
rhs. Then try to merge our lhs and rhs. */
if (TREE_CODE (arg0) == code
&& 0 != (tem = fold_truthop (code, type,
TREE_OPERAND (arg0, 1), arg1)))
return fold_build2 (code, type, TREE_OPERAND (arg0, 0), tem);
A similar hack could be done for fold_range_test.
(I wrote a helper fold_assoc (f, x, code, type, op1, op2) that does this in a
more general way, but it in turn needed `find_assoc_p' and `commutes_p'
functions, and handling EXPR_MINUS was onerous. It might be too slow for
general use. Basically, it needs a fast way to check for common subexpressions
to avoid pointless recursions.)
--
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=21643
^ permalink raw reply [flat|nested] 5+ messages in thread
* [Bug tree-optimization/21643] GCC fails to merge ranges in comparison.
2005-05-18 12:32 [Bug rtl-optimization/21643] New: GCC fails to merge ranges in comparison dwmw2 at infradead dot org
` (2 preceding siblings ...)
2005-05-18 17:21 ` trt at acm dot org
@ 2005-05-18 17:28 ` trt at acm dot org
3 siblings, 0 replies; 5+ messages in thread
From: trt at acm dot org @ 2005-05-18 17:28 UTC (permalink / raw)
To: gcc-bugs
------- Additional Comments From trt at acm dot org 2005-05-18 17:28 -------
Here is a equivalent case that gcc also misses (but beyond scope of
fold-const.c). By the way, since there is a missing final return, can't gcc just
simplify all three functions into "return 1;" :-)
int fish3(unsigned char c)
{
if (c =='"') return 1;
if (c == 0x20) return 1;
if (c < 0x20) return 1;
}
--
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=21643
^ permalink raw reply [flat|nested] 5+ messages in thread
end of thread, other threads:[~2005-05-18 17:28 UTC | newest]
Thread overview: 5+ messages (download: mbox.gz / follow: Atom feed)
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2005-05-18 12:32 [Bug rtl-optimization/21643] New: GCC fails to merge ranges in comparison dwmw2 at infradead dot org
2005-05-18 12:33 ` [Bug rtl-optimization/21643] " dwmw2 at infradead dot org
2005-05-18 12:39 ` [Bug tree-optimization/21643] " pinskia at gcc dot gnu dot org
2005-05-18 17:21 ` trt at acm dot org
2005-05-18 17:28 ` trt at acm dot org
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