[Issue 6505] Wrong code for expression involving 8 floats, only with -O

2015-06-08 Thread via Digitalmars-d-bugs 
https://issues.dlang.org/show_bug.cgi?id=6505

Andrei Alexandrescu  changed:

   What|Removed |Added

Version|D1 & D2 |D2

--

[Issue 6505] Wrong code for expression involving 8 floats, only with -O

2011-08-23 Thread d-bugmail 
http://d.puremagic.com/issues/show_bug.cgi?id=6505


Walter Bright  changed:

   What|Removed |Added

 Status|NEW |RESOLVED
 CC||bugzi...@digitalmars.com
 Resolution||FIXED


--- Comment #4 from Walter Bright  2011-08-23 
15:23:43 PDT ---
https://github.com/D-Programming-Language/dmd/commit/628640f45bbc2bed3e84e835e19cf03ee2c4eafe

https://github.com/D-Programming-Language/dmd/commit/a92f6bf42e547c6978e4e317b4feb2c6610cf518

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[Issue 6505] Wrong code for expression involving 8 floats, only with -O

2011-08-23 Thread d-bugmail 
http://d.puremagic.com/issues/show_bug.cgi?id=6505



--- Comment #3 from Don  2011-08-23 12:19:44 PDT ---
Here's the problem. The scheduler keeps track of the number of
used x87 registers via the "fpustackused" variable.
Each instruction has a "fpuadjust" value which says how many x87
registers it uses.
The problem is CALL instructions. They have fpuadjust = 0.
But, a function returning float returns it in ST(0) --- so fpuadjust
should be +1.
And if it's a complex result, fpuadjust should be +2.
I think it should be possible to put an assert in cgsched.c, line 2491:

   if (tbl[j])
   {
   fpu += tbl[j]->fpuadjust;
+  assert(fpu >= 0);
   if (fpu >= 8)   // if FPU stack overflow

but this would fail at the moment, because the total goes negative
after a call followed by an FSTP.
So it needs to distinguish between each type of call, depending on how
it affects the FPU stack.
I think the bug lies in funccall() in cod1.c; it should be setting
something in 'code' to record how many x87 registers are returned.

Then, there'll be another minor problem: the number of FPU values CAN
reach 8. This is because of the code in push87() in cg87.c, which does
fdecstp; fstp; when the stack is full. So the condition above will
need to change to:
   if (fpu > 8)   // if FPU stack overflow

This is too invasive a change for me to make and test.

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[Issue 6505] Wrong code for expression involving 8 floats, only with -O

2011-08-23 Thread d-bugmail 
http://d.puremagic.com/issues/show_bug.cgi?id=6505



--- Comment #2 from Don  2011-08-23 01:52:36 PDT ---
Thanks bearophile, that reduction is very helpful.

The code loads 8 values on the x87 stack. The eighth one would cause an
overflow, so in cg87.c, push87(), it inserts:

fdecstp;
fstp [EBP - 24];

The next line is:
fld [EBP - 18];

The code passes to the scheduler, where there's a bug: it converts the code to:

fdecstp;
fld [EBP - 18];
fxch ST(1);
fstp [EBP - 24];

This is an x87 stack overflow, since the load happens before space has been
made in the save. The x87 returns a NaN.

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[Issue 6505] Wrong code for expression involving 8 floats, only with -O

2011-08-16 Thread d-bugmail 
http://d.puremagic.com/issues/show_bug.cgi?id=6505


bearophile_h...@eml.cc changed:

   What|Removed |Added

 CC||bearophile_h...@eml.cc


--- Comment #1 from bearophile_h...@eml.cc 2011-08-16 06:37:50 PDT ---
Simplified a little:


double foo() {
return 1.0;
}
void main() {
double a = foo();
double b = foo();
double x = a*a + a*a + a*a + a*a + a*a + a*a + a*a +
   a*b + a*b;
assert(x > 0);
}


---

Asm normal compilation:

_D4test3fooFZdcomdat
fld1
ret

__Dmaincomdat
L0:enter024h,0
callnear ptr _D4test3fooFZd
fstpqword ptr -018h[EBP]
callnear ptr _D4test3fooFZd
fstpqword ptr -010h[EBP]
fldqword ptr -018h[EBP]
fmulqword ptr -010h[EBP]
fldqword ptr -018h[EBP]
fmulqword ptr -010h[EBP]
fldqword ptr -018h[EBP]
fmulqword ptr -018h[EBP]
fldqword ptr -018h[EBP]
fmulqword ptr -018h[EBP]
fldqword ptr -018h[EBP]
fmulqword ptr -018h[EBP]
fldqword ptr -018h[EBP]
fmulqword ptr -018h[EBP]
fldqword ptr -018h[EBP]
fmulqword ptr -018h[EBP]
fldqword ptr -018h[EBP]
fmulqword ptr -018h[EBP]
fdecstp
fstpqword ptr -024h[EBP]
fldqword ptr -018h[EBP]
fmulqword ptr -018h[EBP]
faddpST(1),ST
faddpST(1),ST
faddpST(1),ST
faddpST(1),ST
faddpST(1),ST
faddpST(1),ST
faddpST(1),ST
fldqword ptr -024h[EBP]
faddpST(1),ST
fstpqword ptr -8[EBP]
fldqword ptr -8[EBP]
ftst
fstswAX
sahf
fstpST
jaL7B
movEAX,9
callnear ptr _D4test8__assertFiZv
L7B:xorEAX,EAX
leave
ret



Asm compilation with -O:

_D4test3fooFZdcomdat
fldqword ptr FLAT:_DATA[00h]
ret

__Dmaincomdat
L0:subESP,034h
callnear ptr _D4test3fooFZd
fstpqword ptr 0Ch[ESP]
callnear ptr _D4test3fooFZd
fldqword ptr 0Ch[ESP]
fldqword ptr 0Ch[ESP]
fxchST2
fstpqword ptr 014h[ESP]
fmulqword ptr 014h[ESP]
fxchST1
fldqword ptr 0Ch[ESP]
fxchST1
fmulqword ptr 014h[ESP]
fxchST1
fmulST,ST(0)
fldqword ptr 0Ch[ESP]
fmulST,ST(0)
fldqword ptr 0Ch[ESP]
fmulST,ST(0)
fldqword ptr 0Ch[ESP]
fmulST,ST(0)
fldqword ptr 0Ch[ESP]
fmulST,ST(0)
fldqword ptr 0Ch[ESP]
fmulST,ST(0)
fdecstp
fldqword ptr 0Ch[ESP]
fxchST1
fstpqword ptr [ESP]
fmulST,ST(0)
faddpST(1),ST
faddpST(1),ST
faddpST(1),ST
faddpST(1),ST
faddpST(1),ST
faddpST(1),ST
faddpST(1),ST
fldqword ptr [ESP]
faddpST(1),ST
ftst
fstswAX
fstpST
sahf
jaL84
movEAX,9
callnear ptr _D4test8__assertFiZv
L84addESP,034h
xorEAX,EAX
ret



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