[Bug inline-asm/56884] New: ARM thumb16 mnemonic lsls not recognized for CPU cortex-m0.

["eleventen at gmail dot com" <gcc-bugzilla@gcc.gnu.org>]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56884

             Bug #: 56884
           Summary: ARM thumb16 mnemonic lsls not recognized for CPU
                    cortex-m0.
    Classification: Unclassified
           Product: gcc
           Version: unknown
            Status: UNCONFIRMED
          Severity: minor
          Priority: P3
         Component: inline-asm
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: eleventen@gmail.com


It looks like the inline assembler when -mcpu=cortex=m0 is selected doesn't
recognize the "lsls" mnemonic.  It assembles "lsl" and emits the instruction
that the disassembler identifies as "lsls".

The hitch is that this mismatch requires different inline assembler when the
cpu changes between M0 and M3/M4.  On M3, the "lsl" instruction will not set
the condition flags.

  ---

Given a source file:

void test () {
  __asm volatile ("lsls r0, #1");
}


For Cortex-M0,

elf@cerise lsl-bug > /opt/gcc/bin/arm-none-eabi-gcc -g -Os -c -mcpu=cortex-m0
-mthumb lsl.c -o lsl.o
/tmp/ccuEyZSU.s: Assembler messages:
/tmp/ccuEyZSU.s:29: Error: instruction not supported in Thumb16 mode -- `lsls
r0,#1'

If the instruction is changed to "lsl r0, #1" the compiler is happy and the
emitted machine code is correct.  The disassembler accurately identifies the
instruction as lsls because that's the only form of lsl that the M0 supports.

void test ()
{
  __asm volatile ("lsl r0, #1");
   0:   0040            lsls    r0, r0, #1
}
   2:   4770            bx      lr


So, I think that the issue is only in the inline assembler in that it doesn't
accept the "lsls" opcode....or is there another explanation?


 ---

For references:

elf@cerise lsl-bug > /opt/gcc/bin/arm-none-eabi-gcc -v -mcpu=cortex-m0 -mthumb
Using built-in specs.
COLLECT_GCC=/opt/gcc/bin/arm-none-eabi-gcc
COLLECT_LTO_WRAPPER=/opt/gcc/libexec/gcc/arm-none-eabi/4.7.2/lto-wrapper
Target: arm-none-eabi
Configured with: ../gcc-4.7.2/configure --target=arm-none-eabi
--prefix=/opt/gcc --enable-multilib --enable-languages=c,c++ --with-newlib
--with-gnu-as --with-gnu-ld --disable-nls --disable-shared --disable-threads
--with-headers=newlib/libc/include --disable-libssp --disable-libstdcxx-pch
--disable-libmudflap --disable-libgomp --disable-werror --with-system-zlib
--disable-newlib-supplied-syscalls
Thread model: single
gcc version 4.7.2 (GCC)