[Bug rtl-optimization/82729] adjacent small objects can be initialized with a single store (but aren't for char a[] = "a")

["peter at cordes dot ca" <gcc-bugzilla at gcc dot gnu dot org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=82729

--- Comment #3 from Peter Cordes <peter at cordes dot ca> ---
Oh also, why is MSP430 using 3 byte-stores instead of a mov.w + mov.b for
storing ab[]?  (on the godbolt link in the initial report)


   # msp430-gcc 6.2.1.16) 6.2.1 20161212
        MOV.W   #25185, 6(R1)
        MOV.W   #99, 8(R1)           # abc[]

        MOV.B   #97, 3(R1)
        MOV.B   #98, 4(R1)
        MOV.B   #0, 5(R1)            # ab[]

        MOV.B   #97, 1(R1)
        MOV.B   #0, 2(R1)            # a[]

Even if alignment is required (IDK), either the first two or last two mov.b
instructions for ab[] could combine into a mov.w, like is done for abc[].  Is
that a target bug?

MSP430 is on Godbolt and it's not a RISC with word size > largest immediate, so
I was looking at it to see if it was just an x86 missed optimization.

Like I was saying for ARM, gcc seems to do a poor job on many RISC ISAs with
this, given the redundancy between strings.