http://gcc.gnu.org/bugzilla/show_bug.cgi?id=49257
Summary: -mfpmath=sse generates x87 instructions on 32 bits OS
Product: gcc
Version: 4.5.1
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c
AssignedTo: [email protected]
ReportedBy: [email protected]
Created attachment 24408
--> http://gcc.gnu.org/bugzilla/attachment.cgi?id=24408
simple reproducer
Hi,
Please find attached a simple C program that shows the issue.
I compile it that way:
gcc -O0 simple.c -mfpmath=sse -msse3 -o ok.exe
./ok.exe returns the correct value
gcc -O0 simple.c -mfpmath=sse -msse3 -DRETURN_NAN -o nan.exe
./nan.exe returns a NAN
Both exe use some gcc intrinsic that change the FP stack into mmx registers. It
is expected that if I call a libc function (like printf) without restoring the
stack to its original state (using emms) then I'll have a wrong behavior. But,
here, because of the following assembly code:
.L4:
fildq 72(%esp)
cmpl $0, 76(%esp)
jns .L3
fldt .LC2
faddp %st, %st(1)
.L3:
fstpl 24(%esp)
movsd 24(%esp), %xmm0
mulsd 56(%esp), %xmm0
movsd %xmm0, 40(%esp)
movl 68(%esp), %eax
movl 4(%eax), %edx
movl (%eax), %eax
movl 52(%esp), %ecx
movl %eax, 16(%esp)
movl %edx, 20(%esp)
movq 16(%esp), %mm0
movntq %mm0, (%ecx)
addl $1, 72(%esp)
adcl $0, 76(%esp)
.L2:
cmpl $0, 76(%esp)
jb .L4
cmpl $0, 76(%esp)
ja .L6
cmpl $9, 72(%esp)
jbe .L4
I've got a NAN why I shouldn't !?
The instruction that generates that x87 code is the line
(double)i * coeff; where i is an unsigned long long and coeff is a double.
It works well if for instance 'i' is a long/int/unsigned int.
Maybe that behavior is expected ?
BR
Olivier
