[PATCH 1/2] MIPS/GAS: Fix o32 LD to the base register

["Maciej W. Rozycki" <macro@linux-mips.org>]

Hi,

 Here's another one:

$ cat ld-base.s
	ld	$4, ($4)
$ mips-linux-as -o ld-base.o ld-base.s
$ mips-linux-objdump -d ld-base.o

ld-base.o:     file format elf32-tradbigmips


Disassembly of section .text:

00000000 <.text>:
   0:	8c840000 	lw	a0,0(a0)
   4:	00000000 	nop
   8:	8c850004 	lw	a1,4(a0)

Ouch!

 Fixed thus and regression tested for mips-linux, mips64-linux, 
mipstx39-elf, mipsisa64-elf and mips-ecoff targets and their little-endian 
counterparts.  The new code produced looks like this:

$ mips-linux-objdump -d ld-base.o

ld-base.o:     file format elf32-tradbigmips


Disassembly of section .text:

00000000 <.text>:
   0:	00800821 	move	at,a0
   4:	8c240000 	lw	a0,0(at)
   8:	8c250004 	lw	a1,4(at)

2010-10-17  Maciej W. Rozycki  <macro@linux-mips.org>

	gas/
	* config/tc-mips.c (macro)[M_LD_OB]: Use a temporary register
	when the first load of the pair would overwrite the base
	register needed for the other one.

 OK?  And thanks for your reviews so far -- I'll try to proceed with 
commits ASAP.

  Maciej

binutils-2.20.51-20100925-mips-gas-ld-tmp.patch
Index: binutils-2.20.51/gas/config/tc-mips.c
===================================================================
--- binutils-2.20.51.orig/gas/config/tc-mips.c
+++ binutils-2.20.51/gas/config/tc-mips.c
@@ -7346,9 +7346,19 @@ macro (struct mips_cl_insn *ip)
 
     case M_LD_OB:
       s = HAVE_64BIT_GPRS ? "ld" : "lw";
+      if (!HAVE_64BIT_GPRS && treg == breg && breg != ZERO)
+	{
+	  /* First load would overwrite the base register, use a
+	     temporary register.  */
+	  used_at = 1;
+	  macro_build (NULL, ADDRESS_ADD_INSN, "d,v,t", AT, breg, ZERO);
+	  breg = AT;
+	}
       goto sd_ob;
+
     case M_SD_OB:
       s = HAVE_64BIT_GPRS ? "sd" : "sw";
+
     sd_ob:
       macro_build (&offset_expr, s, "t,o(b)", treg, BFD_RELOC_LO16, breg);
       if (!HAVE_64BIT_GPRS)