hi,
I find that you are asking only gcc related parts,that is related less,
here they are(from posts on linux-mips,i cc them to the list in case it is
useful,sorry if it brings you inconvenience):
1.about NaN handling
-----------------begin of the first problem--------------------------------
I am sorry but it seems i can't fix this without ugly changes.
since i am not familiar with gcc code, i decide to leave it to you,
but provide some information instead.
In gcc there are 3 spaces where the NaN handling is assumed the
Intel way.
1. gcc/real.c (the most important one)
here the author seems to have known the NaN pattern problem,so
he leaves a interface macro for defining non intel NaN patterns:
(comment of function "make_nan()",at about line 6219)
/* Output a binary NaN bit pattern in the target machine's format. */
/* If special NaN bit patterns are required, define them in tm.h
as arrays of unsigned 16-bit shorts. Otherwise, use the default
patterns here. */
I have read through this file and decided that the follow defined should
be enough for mips:
/* NaN pattern,mips QNAN & SNAN is different from intel's
* DFMODE_NAN and SFMODE_NAN is used in real.c */
#define DFMODE_NAN \
unsigned short DFbignan[4] = {0x7ff7, 0xffff, 0xffff, 0xffff}; \
unsigned short DFlittlenan[4] = {0xffff, 0xffff, 0xffff, 0xfff7}
#define SFMODE_NAN \
unsigned short SFbignan[2] = {0x7fbf, 0xffff}; \
unsigned short SFlittlenan[2] = {0xffff, 0xffbf}
But the problem is where to put them:(. Obviously it is target specified
definitions and should be in config/mips/. Documents say tm.h is a symbol
link and included in config.h,but it is no long true.If i add them to xm-mips.h
then for native compilation it is ok but it fails for cross-compile.
2.gcc/reg-stack.c (H.J. tell me it is not used on mips)
There is a hardcoded QNaN used around line 477:
nan = gen_lowpart (SFmode, GEN_INT (0x7fc00000));
I sugest defining a macro QNAN_HAS_1ST_FRACBIT_CLEARED for mips and change
it to,just don't know where to put it:
#ifndef QNAN_HAS_1ST_FRACBIT_CLEARED
nan = gen_lowpart (SFmode, GEN_INT (0x7fc00000));
#else
nan = gen_lowpart (SFmode, GEN_INT (0x7fbfffff));
#endif
3. config/fp-bit.c (H.J. said it is not mean to target specified)
this is for machine having no fpu hardware.
again i susgest define QNAN_HAS_1ST_FRACBIT_CLEARED and then apply this patch:
190d189
< #ifndef QNAN_HAS_1ST_FRACBIT_CLEARED
192,195d190
< #else
< fraction &= ~QUIET_NAN;
< #endif
<
379,380d373
<
< #ifndef QNAN_HAS_1ST_FRACBIT_CLEARED
382,384d374
< #else
< if (!(fraction & QUIET_NAN))
< #endif
ÔÚ 2002-02-03 22:54:00 you wrote£º
>On Mon, Feb 04, 2002 at 02:22:48PM +0800, Zhang Fuxin wrote:
>> hi,
>>
>> Gcc (2.96 20000731,H.J.LU's rh port for mips) think 0x7fc00000 is QNaN and
>> optimize 0.0/0.0 as 0x7fc00000 for single precision ops,while for my cpu
>> (maybe most mips cpu) is a SNaN. R4k user's manual and "See Mips Run" both
>> say so.And experiments confirm this.
>>
>> Should we correct it?
>
>Yes. Do you have a patch?
>
>Thanks.
>
>
>H.J.
-------------------------end of first problem--------------------------------
--------------------------begin of the second problem------------------------
2. gcc -O2 optimization bug No.1
It seems gcc with optimization > -O2 will produce incorrect code for fp code:
I find this example when tracking down the libm-test failures.
( expf(NaN) == NaN will report an extra "invalid operation" exception )
The faulting code snippet is(from glibc/sysdeps/ieee754/flt-32/w_expf.c):
float __my_expf(float x) /* wrapper expf */
{
float z;
unsigned int hx;
z = __ieee754_expf(x);
if(_LIB_VERSION == _IEEE_) return z;
if(__finitef(x)) {
if(x>o_threshold)
return 1.0;
else if(x<u_threshold)
return 2.0;
printf("haha\n");
}
return z;
}
with -O2(or higher),some statements inside "if (__finitef(x))" are put before
testing the return value of __finitef(x),one of which is a c.lt.s that cause
the extra "invalid operation" exception being raised.
the obj codes is listed below:
1. without -O
0000000000401290 <__my_expf>:
401290: 3c1c0fc0 lui gp,0xfc0
401294: 279c6dd0 addiu gp,gp,28112
401298: 0399e021 addu gp,gp,t9
40129c: 27bdffd0 addiu sp,sp,-48
4012a0: afbc0010 sw gp,16(sp)
4012a4: afbf0028 sw ra,40(sp)
4012a8: afbe0024 sw s8,36(sp)
4012ac: afbc0020 sw gp,32(sp)
4012b0: 03a0f021 move s8,sp
4012b4: e7cc0030 swc1 $f12,48(s8)
4012b8: c7cc0030 lwc1 $f12,48(s8)
4012bc: 8f998088 lw t9,-32632(gp)
4012c0: 00000000 nop
4012c4: 0320f809 jalr t9
4012c8: 00000000 nop
4012cc: 8fdc0010 lw gp,16(s8)
4012d0: e7c00018 swc1 $f0,24(s8)
4012d4: 8f8380ac lw v1,-32596(gp)
4012d8: 00000000 nop
4012dc: 8c630000 lw v1,0(v1)
4012e0: 2402ffff li v0,-1
4012e4: 14620004 bne v1,v0,4012f8 <__my_expf+0x68>
4012e8: 00000000 nop
4012ec: c7c00018 lwc1 $f0,24(s8)
4012f0: 10000032 b 4013bc <__my_expf+0x12c>
4012f4: 00000000 nop
4012f8: c7cc0030 lwc1 $f12,48(s8)
4012fc: 8f998090 lw t9,-32624(gp)
401300: 00000000 nop
401304: 0320f809 jalr t9
401308: 00000000 nop
40130c: 8fdc0010 lw gp,16(s8)
401310: 10400029 beqz v0,4013b8 <__my_expf+0x128>
401314: 00000000 nop
401318: c7c20030 lwc1 $f2,48(s8)
40131c: 8f818018 lw at,-32744(gp)
401320: 00000000 nop
401324: 242142a0 addiu at,at,17056
401328: c4200000 lwc1 $f0,0(at)
40132c: 00000000 nop
401330: 4602003c c.lt.s $f0,$f2
401334: 00000000 nop
401338: 45010003 bc1t 401348 <__my_expf+0xb8>
40133c: 00000000 nop
401340: 10000005 b 401358 <__my_expf+0xc8>
401344: 00000000 nop
401348: 3c013f80 lui at,0x3f80
40134c: 44810000 mtc1 at,$f0
401350: 1000001a b 4013bc <__my_expf+0x12c>
401354: 00000000 nop
401358: c7c20030 lwc1 $f2,48(s8)
40135c: 8f818018 lw at,-32744(gp)
401360: 00000000 nop
401364: 242142a4 addiu at,at,17060
401368: c4200000 lwc1 $f0,0(at)
40136c: 00000000 nop
401370: 4600103c c.lt.s $f2,$f0
401374: 00000000 nop
401378: 45010003 bc1t 401388 <__my_expf+0xf8>
40137c: 00000000 nop
401380: 10000005 b 401398 <__my_expf+0x108>
401384: 00000000 nop
401388: 3c014000 lui at,0x4000
40138c: 44810000 mtc1 at,$f0
401390: 1000000a b 4013bc <__my_expf+0x12c>
401394: 00000000 nop
401398: 8f848018 lw a0,-32744(gp)
40139c: 00000000 nop
4013a0: 248442a8 addiu a0,a0,17064
4013a4: 8f998058 lw t9,-32680(gp)
4013a8: 00000000 nop
4013ac: 0320f809 jalr t9
4013b0: 00000000 nop
4013b4: 8fdc0010 lw gp,16(s8)
4013b8: c7c00018 lwc1 $f0,24(s8)
4013bc: 03c0e821 move sp,s8
4013c0: 8fbf0028 lw ra,40(sp)
4013c4: 8fbe0024 lw s8,36(sp)
4013c8: 03e00008 jr ra
4013cc: 27bd0030 addiu sp,sp,48
2. with -O2
0000000000400fc0 <__my_expf>:
400fc0: 3c1c0fc0 lui gp,0xfc0
400fc4: 279c70a0 addiu gp,gp,28832
400fc8: 0399e021 addu gp,gp,t9
400fcc: 27bdffd0 addiu sp,sp,-48
400fd0: afbc0010 sw gp,16(sp)
400fd4: e7b60028 swc1 $f22,40(sp)
400fd8: e7b7002c swc1 $f23,44(sp)
400fdc: e7b40020 swc1 $f20,32(sp)
400fe0: e7b50024 swc1 $f21,36(sp)
400fe4: afbf001c sw ra,28(sp)
400fe8: 46006506 mov.s $f20,$f12
400fec: afbc0018 sw gp,24(sp)
400ff0: 8f998088 lw t9,-32632(gp)
400ff4: 00000000 nop
400ff8: 0320f809 jalr t9
400ffc: 00000000 nop
401000: 8fbc0010 lw gp,16(sp)
401004: 00000000 nop
401008: 8f8380ac lw v1,-32596(gp)
40100c: 00000000 nop
401010: 8c630000 lw v1,0(v1)
401014: 2402ffff li v0,-1
401018: 46000586 mov.s $f22,$f0
40101c: 10620021 beq v1,v0,4010a4 <__my_expf+0xe4>
401020: 4600a306 mov.s $f12,$f20
401024: 8f998090 lw t9,-32624(gp)
401028: 00000000 nop
40102c: 0320f809 jalr t9
401030: 00000000 nop
401034: 8fbc0010 lw gp,16(sp)
401038: 3c0142b1 lui at,0x42b1
40103c: 34217180 ori at,at,0x7180
401040: 44811000 mtc1 at,$f2
401044: 3c013f80 lui at,0x3f80
401048: 44810000 mtc1 at,$f0
40104c: 4614103c c.lt.s $f2,$f20 // this is wrongly put ahead ?
401050: 10400013 beqz v0,4010a0 <__my_expf+0xe0>
401054: 00000000 nop
401058: 45010012 bc1t 4010a4 <__my_expf+0xe4>
40105c: 00000000 nop
401060: 3c01c2cf lui at,0xc2cf
401064: 3421f1b5 ori at,at,0xf1b5
401068: 44810000 mtc1 at,$f0
40106c: 8f848018 lw a0,-32744(gp)
401070: 00000000 nop
401074: 24843fa8 addiu a0,a0,16296
401078: 4600a03c c.lt.s $f20,$f0
40107c: 3c014000 lui at,0x4000
401080: 44810000 mtc1 at,$f0
401084: 45010007 bc1t 4010a4 <__my_expf+0xe4>
401088: 00000000 nop
40108c: 8f998058 lw t9,-32680(gp)
401090: 00000000 nop
401094: 0320f809 jalr t9
401098: 00000000 nop
40109c: 8fbc0010 lw gp,16(sp)
4010a0: 4600b006 mov.s $f0,$f22
4010a4: 8fbf001c lw ra,28(sp)
4010a8: c7b60028 lwc1 $f22,40(sp)
4010ac: c7b7002c lwc1 $f23,44(sp)
4010b0: c7b40020 lwc1 $f20,32(sp)
4010b4: c7b50024 lwc1 $f21,36(sp)
4010b8: 03e00008 jr ra
4010bc: 27bd0030 addiu sp,sp,48
----------------------------end of the second problem------------------------
----------------------------begin of 3rd problem-----------------------------
3.wrong code from gcc -O2,No.2
hi,
it seems fixed in latest gcc (3.1). gcc 2.96 does produce wrong code
for -O2, i posted another example one or two days ago.
ÔÚ 2002-02-08 19:37:00 you wrote£º
>I found gcc 2.96 (gcc-2.96-99.1.mipsel.rpm in H.J.Lu's RedHat 7.1)
>outputs wrong code for this short program.
>
>int foo(unsigned long long a, unsigned long long b)
>{
> int as, bs;
> as = a >> 63;
> bs = b >> 63;
> if (as != bs)
> return as || !(b << 1);
> return (a == b) || as;
>}
>
>int main(int argc, char **argv)
>{
> return foo(0, 0xffffffffffffffffull);
>}
>
>This program must return 0. But compiling with -O2 it returns 1 !!
>
># gcc -O -o foo foo.c;./foo;echo $?
>0
># gcc -O2 -o foo foo.c;./foo;echo $?
>1
>
>Output wth -O -g are:
>
>00400780 <foo>:
> 400780: 3c1c0fc0 lui gp,0xfc0
> 400784: 279c78b0 addiu gp,gp,30896
> 400788: 0399e021 addu gp,gp,t9
> 40078c: 00804021 move t0,a0
> 400790: 00a04821 move t1,a1
> 400794: 000917c2 srl v0,t1,0x1f
> 400798: 00402821 move a1,v0
> 40079c: 000717c2 srl v0,a3,0x1f
> 4007a0: 10a2000d beq a1,v0,4007d8 <foo+0x58>
> 4007a4: 00001821 move v1,zero
> 4007a8: 14a00008 bnez a1,4007cc <foo+0x4c>
> 4007ac: 00004021 move t0,zero
> 4007b0: 00071840 sll v1,a3,0x1
> 4007b4: 000627c2 srl a0,a2,0x1f
> 4007b8: 00641825 or v1,v1,a0
> 4007bc: 00061040 sll v0,a2,0x1
> 4007c0: 00621025 or v0,v1,v0
> 4007c4: 14400002 bnez v0,4007d0 <foo+0x50>
> 4007c8: 00000000 nop
> 4007cc: 24080001 li t0,1
> 4007d0: 03e00008 jr ra
> 4007d4: 01001021 move v0,t0
> 4007d8: 15060003 bne t0,a2,4007e8 <foo+0x68>
> 4007dc: 00001021 move v0,zero
> 4007e0: 11270003 beq t1,a3,4007f0 <foo+0x70>
> 4007e4: 00000000 nop
> 4007e8: 10a00002 beqz a1,4007f4 <foo+0x74>
> 4007ec: 00000000 nop
> 4007f0: 24020001 li v0,1
> 4007f4: 03e00008 jr ra
> 4007f8: 00000000 nop
>
>Output with -O2 -g are:
>
>00400780 <foo>:
> 400780: 3c1c0fc0 lui gp,0xfc0
> 400784: 279c78b0 addiu gp,gp,30896
> 400788: 0399e021 addu gp,gp,t9
> 40078c: 00805021 move t2,a0
> 400790: 00c04021 move t0,a2
> 400794: 00a05821 move t3,a1
> 400798: 00e04821 move t1,a3
> 40079c: 000b17c2 srl v0,t3,0x1f
> 4007a0: 000927c2 srl a0,t1,0x1f
> 4007a4: 00001821 move v1,zero
> 4007a8: 1044000a beq v0,a0,4007d4 <foo+0x54>
> 4007ac: 00002821 move a1,zero
> 4007b0: 14400006 bnez v0,4007cc <foo+0x4c>
> 4007b4: 24050001 li a1,1
> 4007b8: 00091840 sll v1,t1,0x1
> 4007bc: 000827c2 srl a0,t0,0x1f
> 4007c0: 00641825 or v1,v1,a0
> 4007c4: 00081040 sll v0,t0,0x1
> 4007c8: 00621025 or v0,v1,v0
> 4007cc: 03e00008 jr ra
> 4007d0: 00a01021 move v0,a1
> 4007d4: 15480003 bne t2,t0,4007e4 <foo+0x64>
> 4007d8: 00001821 move v1,zero
> 4007dc: 11690003 beq t3,t1,4007ec <foo+0x6c>
> 4007e0: 00000000 nop
> 4007e4: 10400002 beqz v0,4007f0 <foo+0x70>
> 4007e8: 00000000 nop
> 4007ec: 24030001 li v1,1
> 4007f0: 03e00008 jr ra
> 4007f4: 00601021 move v0,v1
>
>
>It seems one 'bnez' in good code (at 4007c4) was lost in bad code.
>
>Is this a know problem? If so, is there any patches available?
>
>Thank you.
>---
>Atsushi Nemoto
-----------------------------end of 3rd problem------------------------
ÔÚ 2002-02-18 09:16:00 you wrote£º
>Hi Zhang,
>
>we're talking to Algorithmics about the possibility of productizing their
>SDE compiler for Linux. If this materializes, we should be able to get the
>GCC issues you mention fixed.
>
>Could you therefore pls. send me examples showing all the GCC issues you
>mention:
>
>1) SNan & QNan handling wrong
>2) Wrong code generated with -O2 (exception handling problem)
>3) Wrong code generated with -O2 (long long type problem)
>
>I would like (small!) examples suitable for inclusion directly in a work
>specification, so items like "Mozilla doesn't run" is not good enough :-)
>
>Finally, Kjeld E. at MIPS is spending some time on math-emu. So if you have
>specific issues, you can try to mail him as well (kjelde@mips.com).
>
>Problem #4 you report could be either in glibc or math-emu. If it's math-emu
>we'll fix it.
>
>/Hartvig
>
>
>Zhang Fuxin writes:
>>
>> hi,
>> There are so many problems on math handling for linux-mips,including:
>> 1. SNaN & QNan handling(both gcc & glibc)
>> 2. gcc2.96 generates wrong code with -O2,at least
>> one will lead to exception handling problem(reported by me)
>> one will lead to some 'long long' type mishandling(reported by Atsushi Nemoto)
>>
>> (gcc3.1 seems a lot better,but it has problem to compile glibc.I can't even compile
>> current glibc cvs code(with dl-conflict.c etc patched) with it. The best result is
>> a segment fault when using ld.so.1:
>> ../elf/ld.so.1 --library-path ..:../math:../elf:../dlfcn:../nss:../nis:../rt:../resolv:
>> ../crypt:../linuxthreads ./rpcgen -Y ../scripts -c rpcsvc/bootparam_prot.x -o
>> xbootparam_prot.T
>> make[1]: *** [xbootparam_prot.stmp] Segmentation fault
>> )
>> 3. problems with math-emu
>> 4. other problems to be investigated for its cause,including this one,
>>
>> pow(2,7) = 128.0 when rounding = TONEAREST or UPWARD
>> = 64.1547.. when rounding = DOWNWARD or TOWARDZERO
>>
>> when today i find out the above problem I was feeling almost despaired:(
>>
>> I want to fix these problems,if i could.But it concerns so many things that i am not
>> expert on and no time to dig:(. So any help will be highly appreciated.
>>
>>
>>
>>
>> Regards
>> Zhang Fuxin
>> fxzhang@ict.ac.cn
Regards
Zhang Fuxin
fxzhang@ict.ac.cn
