[Bug target/49641] New: [ARM] Wrong code for ARMv4T and stmia

["sebastian dot huber at embedded-brains dot de" <gcc-bugzilla at gcc dot gnu dot org>]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=49641

           Summary: [ARM] Wrong code for ARMv4T and stmia
           Product: gcc
           Version: 4.6.1
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: target
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: sebastian.huber@embedded-brains.de
            Target: arm-rtemseabi4.11


Created attachment 24689
  --> http://gcc.gnu.org/bugzilla/attachment.cgi?id=24689
Sample code.

The attached source code generates the following assembler code:

00000000 <_Watchdog_Handler_initialization>:
   0:   2200            movs    r2, #0
   2:   4b06            ldr     r3, [pc, #24]   ; (1c
<_Watchdog_Handler_initialization+0x1c>)
   4:   601a            str     r2, [r3, #0]
   6:   4b06            ldr     r3, [pc, #24]   ; (20
<_Watchdog_Handler_initialization+0x20>)
   8:   601a            str     r2, [r3, #0]
   a:   4b06            ldr     r3, [pc, #24]   ; (24
<_Watchdog_Handler_initialization+0x24>)
   c:   601a            str     r2, [r3, #0]
   e:   4b06            ldr     r3, [pc, #24]   ; (28
<_Watchdog_Handler_initialization+0x28>)
  10:   1d19            adds    r1, r3, #4
  12:   c30e            stmia   r3!, {r1, r2, r3}
  14:   4b05            ldr     r3, [pc, #20]   ; (2c
<_Watchdog_Handler_initialization+0x2c>)
  16:   1d19            adds    r1, r3, #4
  18:   c30e            stmia   r3!, {r1, r2, r3}
  1a:   4770            bx      lr

In particular it generates: stmia r3!, {r1, r2, r3}

This instruction leads to UNPREDICTABLE behavior.  According to "ARM
Architecture Reference Manual, Issue I" we have in section "A7.1.57 STMIA",
"Operand restrictions":

"If <Rn> is specified in <registers>:
 o If <Rn> is the lowest-numbered register specified in <registers>, the
original value of <Rn> is stored.
 o Otherwise, the stored value of <Rn> is UNPREDICTABLE."

Since r3 is not the lowest-numbered register specified in {r1, r2, r3} the
stored value of r3 is UNPREDICTABLE.