🚀 go-pugleaf

In generating code to extract values from fields, the compiler uses only the
extv/extvz instructions.  The optimizer changes all extractions of 
byte/word fields on byte/word boundaries to cvt{b,w}l or movz{b,w}l depending
on the field being signed or unsigned.  However, it does this incorrectly
for word size fields on non-longword boundaries.  The specific transformations
it performs are:

	extv $n*16, $16, A, B  ==>  cvtwl n+A,B
	extvz $n*16, $16, A, B ==>  movzwl n+A,B

The actual address of the field is 2n+A, as we are dealing with a word sized
field and not a byte sized one.  The correct transformations are then:

	extv $n*16, $16, A, B  ==> cvtwl 2n+A,B
	extvz $n*16, $16, A, B ==> movzwl 2n+A,B

The code that implements this is in c21.c and is easily fixed.  The changes
are:


263c263
< 		**	extv	$n*16,$16,A,B	>	cvtwl	n+A,B
---
> 		**	extv	$n*16,$16,A,B	>	cvtwl	2n+A,B
265c265
< 		**	extzv	$n*16,$16,A,B	>	movzwl	n+A,B
---
> 		**	extzv	$n*16,$16,A,B	>	movzwl	2n+A,B
310c310,312
< 				sprintf(regs[RT1], "%d%s%s", coff, regs[RT3][0]=='(' ? "":"+",
---
> 				sprintf(regs[RT1], "%d%s%s",
> 					(flen == 8 ? coff : 2*coff),
> 					(regs[RT3][0] == '(' ? "" : "+"),

Mark Bromley
cornell