hi,
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:
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 -O
000000000400fc0 <__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: 1062000a beq v1,v0,401048 <__my_expf+0x88>
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: 44800000 mtc1 zero,$f0
40103c: 14400002 bnez v0,401048 <__my_expf+0x88>
401040: 00000000 nop
401044: 4600b006 mov.s $f0,$f22
401048: 8fbf001c lw ra,28(sp)
40104c: c7b60028 lwc1 $f22,40(sp)
401050: c7b7002c lwc1 $f23,44(sp)
401054: c7b40020 lwc1 $f20,32(sp)
401058: c7b50024 lwc1 $f21,36(sp)
40105c: 03e00008 jr ra
401060: 27bd0030 addiu sp,sp,48
3. 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
Regards
Zhang Fuxin
fxzhang@ict.ac.cn
