Re: GCC 2.7.2.3 good, EGCS 1.0.3 bad for x86 subtract then test

[Toshiyasu Morita <tm@netcom.com>]

>> This is solved by a patch Jeff sent me just yesterday.
>
> Yea.  But it seems to generally create worse code -- too aggressive about
> copying the source to the destination.  Some tweaking of the heuristic for
> when to copy the source to the destination may be needed to make the change
> generally useful.
> 
> jeff

The patch seems to help some on the SH4; I see it now loading
values directly into fr0 occasionally where it didn't before:

4873:graph3d.ii    ****   min_z = M*(poly.vertices[0].sx-width2) + 
N*(poly.vertices[0].sy-height2) + O;
 1567 0308 57A5                 mov.l   @(20,r10),r7	<- bad!
 1569 030a 7104                 add     #4,r1
 1571 030c 475A                 lds     r7,fpul		<- bad!
 1573 030e F418                 fmov.s  @r1,fr4
 1575 0310 F12D                 float   fpul,fr1	<- bad!
 1577 0312 71FC                 add     #-4,r1
 1579 0314 F218                 fmov.s  @r1,fr2
 1580 0316 52A6                 mov.l   @(24,r10),r2
 1581 0318 F211                 fsub    fr1,fr2
 1582 031a 425A                 lds     r2,fpul
 1583 031c F12D                 float   fpul,fr1
 1585 031e F54C                 fmov    fr4,fr5
 1587 0320 F35C                 fmov    fr5,fr3
 1588 0322 E044                 mov     #68,r0
 1589 0324 F311                 fsub    fr1,fr3
 1590 0326 F0E6                 fmov.s  @(r0,r14),fr0
 1591 0328 F302                 fmul    fr0,fr3
 1592 032a E040                 mov     #64,r0
 1593 032c F0E6                 fmov.s  @(r0,r14),fr0	<- here
 1594 032e F32E                 fmac    fr0,fr2,fr3	<- here
 1595 0330 E048                 mov     #72,r0
 1596 0332 F0E6                 fmov.s  @(r0,r14),fr0
 1597 0334 F300                 fadd    fr0,fr3
...
 1639 0374 F0E6                 fmov.s  @(r0,r14),fr0
 1640 0376 FC2E                 fmac    fr0,fr2,fr12

...but the majority of the cases seem to be missed:

 1731 03f8 FA19                 fmov.s  @r1+,fr10	<- here 
 1733 03fa F522                 fmul    fr2,fr5
 1734 03fc F08C                 fmov    fr8,fr0
4911:graph3d.ii    ****   Q1 = poly.plane.m_cam2tex->m21;
 1736 03fe F619                 fmov.s  @r1+,fr6	<- here 
 1738 0400 F53E                 fmac    fr0,fr3,fr5
 1739 0402 7308                 add     #8,r3
4912:graph3d.ii    ****   Q2 = poly.plane.m_cam2tex->m22;
 1741 0404 F719                 fmov.s  @r1+,fr7
 1743 0406 F138                 fmov.s  @r3,fr1
 1744 0408 F0AC                 fmov    fr10,fr0	<- here 
4913:graph3d.ii    ****   Q3 = poly.plane.m_cam2tex->m23;
4914:graph3d.ii    ****   Q4 = -(Q1*poly.plane.v_cam2tex->x + 
Q2*poly.plane.v_cam2tex->y + Q3*poly.plane.v_cam2tex->z);
 1746 040a F47C                 fmov    fr7,fr4
 1748 040c F51E                 fmac    fr0,fr1,fr5	<- here 
 1750 040e F422                 fmul    fr2,fr4
 1751 0410 F06C                 fmov    fr6,fr0		<- here 
 1752 0412 F43E                 fmac    fr0,fr3,fr4	<- here 	
 1754 0414 FB18                 fmov.s  @r1,fr11	<- here 
4915:graph3d.ii    ****
4916:graph3d.ii    ****   if (Scan::tmap2)
 1756 0416 D26A                 mov.l   L464,r2
 1758 0418 F0BC                 fmov    fr11,fr0	<- here 
 1759 041a F41E                 fmac    fr0,fr1,fr4	<- here
...
4939:graph3d.ii    ****     J1 = P1*Camera::inv_aspect + P4*M;
 1842 04a8 E040                 mov     #64,r0
 1843                   L585:
 1844 04aa F2E6                 fmov.s  @(r0,r14),fr2
 1845 04ac F05C                 fmov    fr5,fr0
 1846 04ae D13F                 mov.l   L459,r1
 1847 04b0 F022                 fmul    fr2,fr0		<- here
 1848 04b2 F118                 fmov.s  @r1,fr1
 1849 04b4 F20C                 fmov    fr0,fr2		<- here
 1850 04b6 F08C                 fmov    fr8,fr0
 1851 04b8 F21E                 fmac    fr0,fr1,fr2	<- here
 1852 04ba E04C                 mov     #76,r0
 1853 04bc FE27                 fmov.s  fr2,@(r0,r14)
4940:graph3d.ii    ****     J2 = P2*Camera::inv_aspect + P4*N;
 1855 04be E044                 mov     #68,r0
 1856 04c0 F2E6                 fmov.s  @(r0,r14),fr2	<- here
 1857 04c2 F05C                 fmov    fr5,fr0
 1858 04c4 F022                 fmul    fr2,fr0		<- here
 1859 04c6 F20C                 fmov    fr0,fr2		<- here
 1860 04c8 F09C                 fmov    fr9,fr0
 1861 04ca F21E                 fmac    fr0,fr1,fr2	<- here
 1862 04cc E050                 mov     #80,r0
 1863 04ce FE27                 fmov.s  fr2,@(r0,r14)
...
4942:graph3d.ii    ****     K1 = Q1*Camera::inv_aspect + Q4*M;
 1871 04da E040                 mov     #64,r0
 1872 04dc F2E6                 fmov.s  @(r0,r14),fr2	<- here
 1873 04de F04C                 fmov    fr4,fr0
 1874 04e0 F022                 fmul    fr2,fr0		<- here
 1875 04e2 F20C                 fmov    fr0,fr2		<- here
 1876 04e4 F06C                 fmov    fr6,fr0
 1877 04e6 F21E                 fmac    fr0,fr1,fr2
 1878 04e8 E058                 mov     #88,r0
 1879 04ea FE27                 fmov.s  fr2,@(r0,r14)
4943:graph3d.ii    ****     K2 = Q2*Camera::inv_aspect + Q4*N;
 1881 04ec E044                 mov     #68,r0
 1882 04ee F2E6                 fmov.s  @(r0,r14),fr2	<- here
 1883 04f0 F04C                 fmov    fr4,fr0
 1884 04f2 F022                 fmul    fr2,fr0		<- here
 1885 04f4 F20C                 fmov    fr0,fr2		<- here
 1886 04f6 F07C                 fmov    fr7,fr0
 1887 04f8 F21E                 fmac    fr0,fr1,fr2	<- here
 1888 04fa E05C                 mov     #92,r0
...

Sometimes these sequences are justified because the value is reused;
e.g.:

	fmov 	@rm,fr9
	fmov	fr9,fr0
	fmac	fr0,frm,frn
...
	(fr0 clobbered)
	fmov	fr9,fr0
	fmac	fr0,frm,frn

however it would be nice if gcc could recognize this and convert this
to:

	fmov	@rm,fr0
	fmov	fr0,fr9
	fmac	fr0,frm,frn
...
	(fr0 clobbered)
	fmov	fr9,fr0
	fmac	fr0,frm,frn

because this sequence gives the scheduler more freedom to move the second 
instruction (fmov fr0,fr9) - it can be moved below the fmac instruction 
if necessary.

The file graph3d.ii is from my stress suite at 
ftp://shell14.ba.best.com/pub.t/~tm2/stress-1.4.tar.gz .

The file matrix.i from the stress suite also elicits the same behavior 
from egcs as well.

Toshi