https://gcc.gnu.org/bugzilla/show_bug.cgi?id=21809
nicbrown changed:
What|Removed |Added
CC||contacts at buymore dot pro
--- Comment #23
--- Additional Comments From pinskia at gcc dot gnu dot org 2005-05-29
17:04 ---
This is a target problem, as the RTL is correct.
Looks like there is a forgotten rounding back to float.
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What|Removed |Added
--- Additional Comments From themis_hv at yahoo dot co dot uk 2005-05-29
17:58 ---
This also occurs with double, using test-case.c but with float replaced with
double, so code fragment looks like:
test-case.c:
#include assert,h
volatile double x = 3;
int main()
{
double a = 1 / x;
x =
--- Additional Comments From pinskia at gcc dot gnu dot org 2005-05-29
18:27 ---
(In reply to comment #5)
Should I put this as separate PR?
Actually this is all a dup of bug 323. The problem is excessive pression,
which most non fp
developers will not know about, read the full PR
--- Additional Comments From themis_hv at yahoo dot co dot uk 2005-05-29
19:01 ---
It should be logical equivalent regardless of how it stored in memory.
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What|Removed |Added
--- Additional Comments From pinskia at gcc dot gnu dot org 2005-05-29
19:06 ---
when you store it to memory the precission goes down (aka rounding) read 323
and all the rest of the
problems related to it.
*** This bug has been marked as a duplicate of 323 ***
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What
--- Additional Comments From themis_hv at yahoo dot co dot uk 2005-05-29
19:18 ---
Surely assigning a float value to another float variable should not cause any
rounding as they are same data type.
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What|Removed |Added
--- Additional Comments From pinskia at gcc dot gnu dot org 2005-05-29
19:24 ---
Please go read the papers. Basically x87 is broken in this respect, use either
a different machine or use
SSE.
*** This bug has been marked as a duplicate of 323 ***
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What|Removed
--- Additional Comments From themis_hv at yahoo dot co dot uk 2005-05-29
19:28 ---
Read the code carefully:
test-case.c:
#include assert,h
volatile float x = 3;
int main()
{
float a = 1 / x;
x = a;
assert(a == x);
}
Notice x = a before assertion, both of these variables are of the
--- Additional Comments From pinskia at gcc dot gnu dot org 2005-05-29
19:31 ---
(In reply to comment #11)
This is *not* related to precission.
This is behaviour, you would expect from a compiler.
For non floating point, yes but floating point is different with respect with
--- Additional Comments From themis_hv at yahoo dot co dot uk 2005-05-29
19:32 ---
(In reply to comment #10)
Please go read the papers. Basically x87 is broken in this respect, use
eithera different machine or use
SSE.
It be good idea to do that by default then?
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What
--- Additional Comments From pinskia at gcc dot gnu dot org 2005-05-29
19:35 ---
(In reply to comment #13)
(In reply to comment #10)
Please go read the papers. Basically x87 is broken in this respect, use
eithera different machine or use
SSE.
It be good idea to do that by
--- Additional Comments From themis_hv at yahoo dot co dot uk 2005-05-29
19:36 ---
It be good idea to do that by default then?
It is on x86_64, remember SSE is not every where.
x86-64 has support for SSE3 so it would use that instead.
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What|Removed
--- Additional Comments From joseph at codesourcery dot com 2005-05-29
19:37 ---
Subject: Re: New: [3.4/4.0/4.1 Regression]
Floating Optimization Bug
On Sun, 29 May 2005, themis_hv at yahoo dot co dot uk wrote:
This case (test-case.c) works with gcc -O0 without a problem.
But
--- Additional Comments From pinskia at gcc dot gnu dot org 2005-05-29
19:43 ---
(In reply to comment #15)
x86-64 has support for SSE3 so it would use that instead.
Actually that is wrong, the subset which is supported by AMD and Intel (EM64T)
only have SSE, SSE2,
and MMX. AMD's
--- Additional Comments From themis_hv at yahoo dot co dot uk 2005-05-29
19:46 ---
Again just use -ffloat-store as required not get the excessive precision.
This should included in gcc spec file by defaults.
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What|Removed |Added
--- Additional Comments From pinskia at gcc dot gnu dot org 2005-05-29
19:47 ---
That is not going to change, the assert is allowed to fail by the standard by
the way.
*** This bug has been marked as a duplicate of 323 ***
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What|Removed |Added
--- Additional Comments From themis_hv at yahoo dot co dot uk 2005-05-29
19:51 ---
(In reply to comment #19)
That is not going to change, the assert is allowed to fail by the standard by
the way.
Yes, assert fails in some cases (I think of a hundred at moment!).
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--- Additional Comments From pinskia at gcc dot gnu dot org 2005-05-29
19:56 ---
(In reply to comment #20)
Yes, assert fails in some cases (I think of a hundred at moment!).
See now you did not read my comment, I said it is _ALLOWED by the
standard to ___FAIL___.
How much
--- Additional Comments From themis_hv at yahoo dot co dot uk 2005-05-29
20:09 ---
You seem like someone who does not want to do the leg work
of getting your programs fixed so you don't depend on this.
Regardless, other poeple dependant on it.
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