[Bug target/39469] Calculated values replaced with constants even if the constants cost more than the calculations

[siarhei.siamashka at gmail dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=39469

--- Comment #6 from Siarhei Siamashka <siarhei.siamashka at gmail dot com> 2012-12-10 00:24:12 UTC ---
(In reply to comment #5)
> (In reply to comment #4)
> > The ARM backend should do a splitter just like the rs6000 back-end does if it
> > is faster/smaller to load a constant via the instructions.
> 
> I'm not sure if rs6000 is any better. It looks just as bad as ARM, based on my
> experience trying to optimize
> http://lists.freedesktop.org/archives/pixman/2012-December/002394.html

And the testcase attached to this bug compiles to the following code with
powerpc-unknown-linux-gnu-gcc (-O2 optimizations):

    .file    "test.c"
    .section    ".text"
    .align 2
    .globl foo
    .type    foo, @function
foo:
    lis 8,0x5f5
    lis 10,array@ha
    ori 8,8,57600
    la 9,array@l(10)
    stw 8,array@l(10)
    lis 10,0xbeb
    ori 10,10,49664
    stw 10,4(9)
    lis 10,0x17d7
    ori 10,10,33792
    stw 10,8(9)
    lis 10,0x2faf
    ori 10,10,2048
    stw 10,12(9)
    blr
    .size    foo, .-foo
    .align 2
    .globl bar
    .type    bar, @function
bar:
    lis 10,array@ha
    slwi 6,3,1
    la 9,array@l(10)
    slwi 7,3,2
    slwi 8,3,3
    stw 3,array@l(10)
    stw 6,4(9)
    stw 7,8(9)
    stw 8,12(9)
    blr
    .size    bar, .-bar
    .ident    "GCC: (GNU) 4.8.0 20121209 (experimental)"
    .section    .note.GNU-stack,"",@progbits

That's 15 instructions in "foo" vs. 10 in "bar". For MIPS the difference is 16
instructions vs. 11 (I'm not posting the code because it is rather similar).

Is this really an ARM target bug?