Thumb: Do not convert "sub r?, #0" into "add r?, #0"

[Nick Clifton]

Hi Guys,

  I am applying the patch below to fix a small bug in the ARM
  assembler:  In thumb mode it would convert a subtract of zero into
  an add of zero.  This does not work because the semantics for the
  setting of the Carry flag are different.  The patch also includes a
  test case to make sure that this bug does not recur.

Cheers
        Nick

2002-05-02  Nick Clifton  <address@hidden>

        * config/tc-arm.c (thumb_add_sub): Do not convert a subtract of
        zero into an add of zero - it is not the same.

2002-05-02  Nick Clifton  <address@hidden>

        * gas/arm/arm7t.s: Add thumb mode "sub r?, #0" and "add r?, #0".
        * gas/arm/arm7t.d: Add expected results.  (Make sure that the
        subtract is not converted into an add).

Index: gas/config/tc-arm.c
===================================================================
RCS file: /cvs/src/src/gas/config/tc-arm.c,v
retrieving revision 1.117
diff -c -3 -p -w -r1.117 tc-arm.c
*** gas/config/tc-arm.c 21 Mar 2002 09:13:34 -0000      1.117
--- gas/config/tc-arm.c 2 May 2002 09:05:31 -0000
*************** thumb_add_sub (str, subtract)
*** 7447,7453 ****
                  return;
                }
            }
!         else
            subtract = 0;
  
          if (Rd == REG_SP)
--- 7447,7455 ----
                  return;
                }
            }
!         /* Note - you cannot convert a subtract of 0 into an
!            add of 0 because the carry flag is set differently.  */
!         else if (offset > 0)
            subtract = 0;
  
          if (Rd == REG_SP)

Index: gas/testsuite/gas/arm/arm7t.s
===================================================================
RCS file: /cvs/src/src/gas/testsuite/gas/arm/arm7t.s,v
retrieving revision 1.3
diff -c -3 -p -w -r1.3 arm7t.s
*** gas/testsuite/gas/arm/arm7t.s       1 Nov 1999 17:10:27 -0000       1.3
--- gas/testsuite/gas/arm/arm7t.s       2 May 2002 09:05:31 -0000
*************** misc:
*** 72,74 ****
--- 72,82 ----
        .align
  .L2:
        .word   fred
+       
+       .ltorg
+       .thumb
+       .global thumb_tests
+       .thumb_func
+ thumb_tests:  
+       sub     r0, #0
+       add     r0, #0

Index: gas/testsuite/gas/arm/arm7t.d
===================================================================
RCS file: /cvs/src/src/gas/testsuite/gas/arm/arm7t.d,v
retrieving revision 1.6
diff -c -3 -p -w -r1.6 arm7t.d
*** gas/testsuite/gas/arm/arm7t.d       16 Jul 2001 19:06:09 -0000      1.6
--- gas/testsuite/gas/arm/arm7t.d       2 May 2002 09:05:31 -0000
*************** Disassembly of section .text:
*** 66,68 ****
--- 66,70 ----
  [             ]*dc:.*fred
  0+e0 <[^>]*> 0000c0de ?       .*
  0+e4 <[^>]*> 0000dead ?       .*
+ 0+e8 <[^>]*> 3800             sub     r0, #0
+ 0+ea <[^>]*> 3000             add     r0, #0