Path: utzoo!utgpu!jarvis.csri.toronto.edu!rutgers!tut.cis.ohio-state.edu!DG-RTP.DG.COM!wood
From: wood@DG-RTP.DG.COM (Tom Wood)
Newsgroups: gnu.gcc.bug
Subject: Loop invariant regression with 1.36.93
Message-ID: <9002011343.AA13564@gen-rtx.rtp.dg.com>
Date: 1 Feb 90 13:43:25 GMT
Sender: daemon@tut.cis.ohio-state.edu
Reply-To: wood@dg-rtp.dg.com
Distribution: gnu
Organization: Data General, RTP, NC
Lines: 100

I've been installing the 1.36.93 changes into GCC 1.36 for the 88k.
In doing so, I came across this "performance regression".  The problem
is that the changes to loop.c from 1.36.00 to 1.36.93 fail to note
that piecemax[i] is invariant.  It appears this is the case for global
variables in general.  Here's the function from the Stanford benchmark
bench.c:

    int Fit (i, j) int i, j;
	{
	int k;
	for ( k = 0; k <= piecemax[i]; k++ )
	    if ( p[i][k] ) if ( puzzl[j+k] ) return (false);
	return (true);
	};

Here's what I get with the 1.36.93 version of loop.c.  This is real
fancy, and an improvement except for the reloading of piecemax[i]
after @L128.

	file	 "bench.c"

; Cc1 (1.36.4) arguments:
; -fdelayed-branch -fomit-frame-pointer -quiet -dumpbase -O -o

_Fit:
	or	 r8,r0,r2
	or	 r9,r0,r0
	or.u	 r12,r0,hi16(_piecemax)
	or	 r12,r12,lo16(_piecemax)
	ld	 r12,r12[r8]
	cmp	 r10,r9,r12
	bb0.n	 le,r10,@L132
	or	 r7,r0,r3
	or.u	 r12,r0,hi16(_p)
	or	 r12,r12,lo16(_p)
	mak	 r11,r8,0<11>
	addu	 r11,r12,r11
	or.u	 r6,r0,hi16(_puzzl)
	or	 r6,r6,lo16(_puzzl)
@L131:
	ld	 r12,r11[r9]
	bcnd	 eq0,r12,@L128
	addu	 r12,r7,r9
	ld	 r12,r6[r12]
	bcnd	 eq0,r12,@L128
	br.n	 @L125
	or	 r2,r0,r0
@L128:
	addu	 r9,r9,0x0001			; 1
	or.u	 r12,r0,hi16(_piecemax)
	or	 r12,r12,lo16(_piecemax)
	ld	 r12,r12[r8]
	cmp	 r10,r9,r12
	bb1	 le,r10,@L131
@L132:
	or	 r2,r0,0x0001			; 1
@L125:
	jmp	 r1

If I simply back out the loop.c changes entirely, I get the old style
loop.  piecemax[i] is invariant, but puzzl[i] is not an induction
variable.

	file	 "bench.c"

; Cc1 (1.36.4) arguments:
; -fdelayed-branch -fomit-frame-pointer -quiet -dumpbase -O -o

_Fit:
	or	 r6,r0,r3
	or	 r9,r0,r0
	or.u	 r12,r0,hi16(_piecemax)
	or	 r12,r12,lo16(_piecemax)
	ld	 r7,r12[r2]
	or.u	 r12,r0,hi16(_p)
	or	 r12,r12,lo16(_p)
	mak	 r2,r2,0<11>
	br.n	 @L125
	addu	 r8,r12,r2
@L130:
	ld	 r12,r8[r9]
	bcnd	 eq0,r12,@L127
	addu	 r12,r6,r9
	or.u	 r11,r0,hi16(_puzzl)
	or	 r11,r11,lo16(_puzzl)
	ld	 r12,r11[r12]
	bcnd	 eq0,r12,@L127
	br.n	 @L124
	or	 r2,r0,r0
@L127:
	addu	 r9,r9,0x0001			; 1
@L125:
	cmp	 r10,r9,r7
	bb1	 le,r10,@L130
	or	 r2,r0,0x0001			; 1
@L124:
	jmp	 r1

-- 
Tom Wood