Russ Cox 84f291b1bd 8g: compute register liveness during regopt ... Input code like 0000 (x.go:2) TEXT main+0(SB),$36-0 0001 (x.go:3) MOVL $5,i+-8(SP) 0002 (x.go:3) MOVL $0,i+-4(SP) 0003 (x.go:4) MOVL $1,BX 0004 (x.go:4) MOVL i+-8(SP),AX 0005 (x.go:4) MOVL i+-4(SP),DX 0006 (x.go:4) MOVL AX,autotmp_0000+-20(SP) 0007 (x.go:4) MOVL DX,autotmp_0000+-16(SP) 0008 (x.go:4) MOVL autotmp_0000+-20(SP),CX 0009 (x.go:4) CMPL autotmp_0000+-16(SP),$0 0010 (x.go:4) JNE ,13 0011 (x.go:4) CMPL CX,$32 0012 (x.go:4) JCS ,14 0013 (x.go:4) MOVL $0,BX 0014 (x.go:4) SHLL CX,BX 0015 (x.go:4) MOVL BX,x+-12(SP) 0016 (x.go:5) MOVL x+-12(SP),AX 0017 (x.go:5) CDQ , 0018 (x.go:5) MOVL AX,autotmp_0001+-28(SP) 0019 (x.go:5) MOVL DX,autotmp_0001+-24(SP) 0020 (x.go:5) MOVL autotmp_0001+-28(SP),AX 0021 (x.go:5) MOVL autotmp_0001+-24(SP),DX 0022 (x.go:5) MOVL AX,(SP) 0023 (x.go:5) MOVL DX,4(SP) 0024 (x.go:5) CALL ,runtime.printint+0(SB) 0025 (x.go:5) CALL ,runtime.printnl+0(SB) 0026 (x.go:6) RET , is problematic because the liveness range for autotmp_0000 (0006-0009) is nested completely inside a span where BX holds a live value (0003-0015). Because the register allocator only looks at 0006-0009 to see which registers are used, it misses the fact that BX is unavailable and uses it anyway. The n->pun = anyregalloc() check in tempname is a workaround for this bug, but I hit it again because I did the tempname call before allocating BX, even though I then used the temporary after storing in BX. This should fix the real bug, and then we can remove the workaround in tempname. The code creates pseudo-variables for each register and includes that information in the liveness propagation. Then the regu fields can be populated using that more complete information. With that approach, BX is marked as in use on every line in the whole span 0003-0015, so that the decision about autotmp_0000 (using only 0006-0009) still has all the information it needs. This is not specific to the 386, but it only happens in generated code of the form load R1 ... load var into R2 ... store R2 back into var ... use R1 and for the most part the other compilers generate the loads for a given compiled line before any of the stores. Even so, this may not be the case everywhere, so the change is worth making in all three. R=ken2, ken, ken CC=golang-dev https://golang.org/cl/4529106		2011-06-03 14:10:39 -04:00
..
cgen.c	gc: inline append when len<cap	2011-05-11 16:35:11 +02:00
doc.go	tweak documentation of commands	2009-11-09 11:45:15 -08:00
galign.c	gc: delete float, complex	2011-01-19 23:08:11 -05:00
gg.h	6g: avoid too-large immediate constants	2010-10-20 00:40:06 -04:00
ggen.c	gc: typecheck the whole tree before walking. preparation for some escape-analysis related changes.	2011-06-02 18:48:17 +02:00
gobj.c	ld: 25% faster	2011-04-09 09:44:20 -04:00
gsubr.c	gc: inline append when len<cap	2011-05-11 16:35:11 +02:00
list.c	various: avoid %ld etc	2010-10-13 16:20:22 -04:00
Makefile	gc: typecheck the whole tree before walking. preparation for some escape-analysis related changes.	2011-06-02 18:48:17 +02:00
opt.h	sped up optimization by not optimizing	2009-08-29 20:33:21 -07:00
peep.c	1. integer division by a constant done.	2009-08-09 15:16:06 -07:00
reg.c	8g: compute register liveness during regopt	2011-06-03 14:10:39 -04:00