For your questions:
[1]. why the assertion,
asm volatile ("%0" : : "i#*X"(x)); is a wrong assembler statement, it
should be DCEed by optimizer and should not exist in CG phase.
[2]. in order to get DCE. we should make condition
_builtin_constant_p (x)
&& x != 0
be folded to constant 0, intrinsic_op _builtin_constant_p(x) should be
simplified to 0 and then let the optimizer further optimized
_builtin_constant_p (x)
&& x != 0
to 0
[3]. at phase O0, _builtin_constant_p(x) is already folded to 0 by gcc. and
the original case, with the __OPTIMIZE__ macro will not be enabled.
Regards
Gang
On Sat, Dec 17, 2011 at 5:11 PM, Sun Chan <sun.c...@gmail.com> wrote:
> Pls send more info for me to adequately review this fix.
> Why do you suggest this fix. What is the problem with the assertion.
> If you do that at -O0, what would happen?
> Sun
>
> On Sat, Dec 17, 2011 at 12:52 AM, Gang Yu <yugang...@gmail.com> wrote:
>
>> Hi,
>>
>> Could a gatekeeper please help review the fix for bug595(
>> https://bugs.open64.net/show_bug.cgi?id=595)?
>>
>> bug case:
>>
>> extern void doit(int);
>> void
>> quick_doit(int x)
>> {
>> if (__builtin_constant_p (x)
>> && x != 0)
>> asm volatile ("%0" : : "i#*X"(x));
>> else
>> doit(x);
>> }
>> Compiling quick_doit(0)
>> "bug595.c", line 9: Error: Invalid 'asm' constrain : Cannot find
>> immediate operand for ASM
>> opencc ERROR:
>> /fc/proj/ctires/open64/o64guru/OPEN64_X86_DBG/LATEST/bits//lib/gcc-lib/x86_64-open64-linux/5.0/be
>> returned non-zero status 4
>> Analysis:
>> __builtin_constant_p(x) && x !=0 should be directly folded to if 0(it did
>> not), then DCE does unreachable elimination, which finally sent out "doit"
>> to CG.
>>
>> Suggested fix:
>> index 148c4e2..42f55fb 100644
>> --- a/osprey/be/opt/opt_htable.cxx
>> +++ b/osprey/be/opt/opt_htable.cxx
>> @@ -3575,7 +3575,9 @@ CODEMAP::Add_expr(WN *wn, OPT_STAB *opt_stab,
>> STMTREP *stmt, CANON_CR *ccr,
>> ccr->Set_tree(NULL);
>> ccr->Set_scale(retv->Const_val());
>> retv->DecUsecnt();
>> - return FALSE;
>> + // bug595 open64.net. intrinsic op folded to compile constant
>> + // should be marked propogated for further fold/optimizations.
>> + return TRUE;
>> }
>> if (retv->Kind() == CK_RCONST) {
>> ccr->Set_tree(retv);
>> Would a gatekeeper help the review? thanks
>> Regards
>> Gang
>>
>>
>> ------------------------------------------------------------------------------
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>>
>>
>
------------------------------------------------------------------------------
Learn Windows Azure Live! Tuesday, Dec 13, 2011
Microsoft is holding a special Learn Windows Azure training event for
developers. It will provide a great way to learn Windows Azure and what it
provides. You can attend the event by watching it streamed LIVE online.
Learn more at http://p.sf.net/sfu/ms-windowsazure
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