[Bug target/19009] New: Loading of FP constants into FP reg via SSE reg

[Bug target/19009] New: Loading of FP constants into FP reg via SSE reg

[uros at kss-loka dot si]

This is something I noticed in the build of povray-3.50c, with '-march=pentium4
-mfpmath=387'. Loading of 0.0 into the FP register is quite strange:

 8051efb:    66 0f ef c9              pxor   %xmm1,%xmm1        <- clear SSE reg
 8051eff:    f2 0f 11 4c 24 38        movsd  %xmm1,0x38(%esp,1) <- move it to stack
 8051f05:    89 de                    mov    %ebx,%esi
 8051f07:    31 c9                    xor    %ecx,%ecx
 8051f09:    dd 03                    fldl   (%ebx)
 8051f0b:    d8 cd                    fmul   %st(5),%st
 8051f0d:    dd 43 08                 fldl   0x8(%ebx)
 8051f10:    d8 cd                    fmul   %st(5),%st
 8051f12:    de c1                    faddp  %st,%st(1)
 8051f14:    dd 43 10                 fldl   0x10(%ebx)
 8051f17:    d8 cc                    fmul   %st(4),%st
 8051f19:    de c1                    faddp  %st,%st(1)
 8051f1b:    d8 c2                    fadd   %st(2),%st
 8051f1d:    f2 0f 11 0c 24           movsd  %xmm1,(%esp,1) <- move it to stack
 8051f22:    dd 04 24                 fldl   (%esp,1)      <- load it to FP reg
                        
...
 8051f39:    dd 44 24 38              fldl   0x38(%esp,1)  <- load it to FP reg
 8051f3d:    df f1                    fcomip %st(1),%st
...

This could be implemented by fldz...

Another example of constant loading via XMM reg:

 ...
 805552b:    f2 0f 10 05 e0 63 16     movsd  0x81663e0,%xmm0    <- load consant
 8055532:    08
 8055533:    f2 0f 11 44 24 20        movsd  %xmm0,0x20(%esp,1) <- move to stack
 8055539:    dd 44 24 20              fldl   0x20(%esp,1)
 805553d:    df f1                    fcomip %st(1),%st
 ...

-- 
           Summary: Loading of FP constants into FP reg via SSE reg
           Product: gcc
           Version: 4.0.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P2
         Component: target
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: uros at kss-loka dot si
                CC: gcc-bugs at gcc dot gnu dot org
 GCC build triplet: pentium4-pc-linux-gnu
  GCC host triplet: pentium4-pc-linux-gnu
GCC target triplet: pentium4-pc-linux-gnu


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=19009

[Bug target/19009] Loading of FP constants into FP reg via SSE reg

[bangerth at dealii dot org]

------- Additional Comments From bangerth at dealii dot org  2004-12-15 14:13 -------
Uros, do you have a testcase? 

-- 
           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |WAITING


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=19009

[Bug target/19009] Loading of FP constants into FP reg via SSE reg

[uros at kss-loka dot si]

------- Additional Comments From uros at kss-loka dot si  2004-12-16 06:28 -------
(In reply to comment #1)

I'm trying to make a testcase out of PovRay sources that trigger this behaviour.
I think that "*movdf_nointeger" is somehow confused and chooses SSE register to
load constant. After that, reload moves SSE reg to FP reg via stack. Perhaps
ix86_preferred_reload_class () needs some fine-tuning regarding to -mfpmath
parameter?


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=19009

[Bug target/19009] Loading of FP constants into FP reg via SSE reg

[uros at kss-loka dot si]

------- Additional Comments From uros at kss-loka dot si  2004-12-16 13:50 -------
-finline-functions is needed to trigger the bug with -O2. 

The attached testcase should be compiled with '-O2 -march=pentium4 -mfpmath=387
-ffast-math -D__NO_MATH_INLINES -finline-functions' to get:
	...
	pxor	%xmm0, %xmm0
	movsd	%xmm0, -16(%ebp)
	fldl	-16(%ebp)
	fcomip	%st(1), %st
	je	.L23
	fld	%st(0)
	...

and:

grep xmm zero.s
        pxor    %xmm0, %xmm0
        movsd   %xmm0, -16(%ebp)
        movsd   %xmm0, -16(%ebp)
        movsd   %xmm0, -16(%ebp)
        movsd   %xmm0, -16(%ebp)

        movsd   %xmm0, 8(%edx)
        movsd   %xmm0, (%edx)

where movsds are followed by:
	fldl	-16(%ebp)

BTW: "#include <math.h> can be removed from testcase to avoid
-D__NO_MATH_INLINES. Ther result will be the same.


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=19009

[Bug target/19009] Loading of FP constants into FP reg via SSE reg

[uros at kss-loka dot si]

------- Additional Comments From uros at kss-loka dot si  2004-12-16 14:35 -------
Another candidate for TARGET_SSE_MATH cleanup...

(insn 21 20 22 0 (set (reg:CCFP 17 flags)
        (compare:CCFP (reg/v:DF 60 [ mod ])
            (reg:DF 70))) 24 {*cmpfp_i_sse} (nil)
    (nil))


-- 
           What    |Removed                     |Added
----------------------------------------------------------------------------
   Last reconfirmed|0000-00-00 00:00:00         |2004-12-16 14:35:51
               date|                            |


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=19009

[Bug target/19009] Loading of FP constants into FP reg via SSE reg

[pinskia at gcc dot gnu dot org]

-- 
           What    |Removed                     |Added
----------------------------------------------------------------------------
           Severity|normal                      |minor
             Status|WAITING                     |NEW
     Ever Confirmed|                            |1
           Keywords|                            |missed-optimization
   Last reconfirmed|2004-12-16 14:35:51         |2004-12-27 01:00:43
               date|                            |


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=19009

[Bug target/19009] Loading of FP constants into FP reg via SSE reg

[uros at kss-loka dot si]

------- Additional Comments From uros at kss-loka dot si  2005-01-07 11:29 -------
This bugreport shows similar problem for x87 code as PR 19252 shoes for SSE
code. The cause of both probems is described in
http://gcc.gnu.org/ml/gcc-patches/2005-01/msg00394.html

-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=19009

[Bug target/19009] Loading of FP constants into FP reg via SSE reg

[rth at gcc dot gnu dot org]

-- 
           What    |Removed                     |Added
----------------------------------------------------------------------------
         AssignedTo|unassigned at gcc dot gnu   |rth at gcc dot gnu dot org
                   |dot org                     |
             Status|NEW                         |ASSIGNED
   Last reconfirmed|2004-12-27 01:00:43         |2005-01-12 02:49:20
               date|                            |


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=19009

[Bug target/19009] Loading of FP constants into FP reg via SSE reg

[rth at gcc dot gnu dot org]

------- Additional Comments From rth at gcc dot gnu dot org  2005-01-14 00:55 -------
Fixed.

-- 
           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|ASSIGNED                    |RESOLVED
         Resolution|                            |FIXED


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=19009

[Bug target/19009] Loading of FP constants into FP reg via SSE reg

[pinskia at gcc dot gnu dot org]

-- 
           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|---                         |4.0.0


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=19009

[Bug target/19009] Loading of FP constants into FP reg via SSE reg

[uros at kss-loka dot si]

------- Additional Comments From uros at kss-loka dot si  2005-01-14 13:08 -------
It looks that the problem with FP compares forcing constant into wrong register
part of this bug is solved. However, register allocator can still be confused
when a variable is initialized to constant value:

grep fldz povray_dump.sse | wc -l
    117
grep fld1 povray_dump.sse | wc -l
    141
grep pxor povray_dump.387 | wc -l
     20

I'll try to provide a small testcase. The testcase (zero.c) attached to this
bugreport is fixed, but anyway I suggest that we reopen this bug.

-- 
           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|RESOLVED                    |REOPENED
         Resolution|FIXED                       |


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=19009

[Bug target/19009] Loading of FP constants into FP reg via SSE reg

[pinskia at gcc dot gnu dot org]

------- Additional Comments From pinskia at gcc dot gnu dot org  2005-01-14 13:16 -------
(In reply to comment #8)
> It looks that the problem with FP compares forcing constant into wrong register
> part of this bug is solved. However, register allocator can still be confused
> when a variable is initialized to constant value:

Can you open a new one with the full testcase, since this is the register allocator being dumb which is 
usual in GCC.

-- 
           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|REOPENED                    |RESOLVED
         Resolution|                            |FIXED


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=19009