[Bug c/38570] New: 'GCC/THUMB generates sub-optimal prolog/epilog

[daniel dot sherwood at sepura dot com]

When generating relatively trivial leaf-functions that contains local branch
instructions (not calling sub functions), the compiler generates unnecessary
PUSH/POP instructions to store the LR on the stack.

Richard Earnshaw [Richard.Earnshaw@arm.com] has confirmed that this is a bug
and requested that I raise it in bugzilla.

In the attached example (test.c), it can be seen in the generated assembly file
(test-prologue-thumb.s) that all of the wcstrlenN() functions have unnecessary
'push{lr}/pop{pc}' which could be replaced by just doing 'bx lr' in the epilog.

Command line was:

arm-none-eabi-gcc -mthumb -mno-thumb-interwork test.c -Os -S -o
test-prologue-thumb.s


-- 
           Summary: 'GCC/THUMB generates sub-optimal prolog/epilog
           Product: gcc
           Version: unknown
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: daniel dot sherwood at sepura dot com
 GCC build triplet: i686-pc-linux-gnu
  GCC host triplet: i686-mingw32
GCC target triplet: arm-none-eabi


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=38570