mark more things as const in C codegen
|Reported by:||slyfox||Owned by:|
|Type of failure:||None/Unknown||Test Case:|
|Related Tickets:||Differential Rev(s):|
Recently i've tried to build ghc-7.8.2 on ia64 and it overflows so called "short data" section. (it's where global 'static' variables live).
I've looked at low-hanging fruits of squashing such global "variables". One source of them seems to be a string literal.
Consider one-line module:
module B (v) where v = "hello"
in -fvia-C (or unreg) mode it generates code like
static char gibberish_str = "hello";
It uselessly eats data section. The patch switches generator to emit:
static const char gibberish_str = "hello";
- as far as I see native codegens already put ot to .rodata,
thus it should be safe.
- I likely didn't cover more cases, like
- and mysterious pprTop (CmmData _section (Statics lbl [CmmUninitialised size]))
Size of unreg-stage2 on amd64 before and after the patch:
$ size inplace/lib/bin/ghc-stage2 (unpatched) text data bss dec hex filename 81986382 20776344 44096 102806822 620b526 inplace/lib/bin/ghc-stage2 $ size inplace/lib/bin/ghc-stage2 (patched) text data bss dec hex filename 83648494 19062936 44096 102755526 61fecc6 inplace/lib/bin/ghc-stage2
Text section increased for 1.6MBs (consts moved here, likely .rodata actually), data section decreased for 1.7MBs.
I think with minor fiddling with linker flags we can merge equal constants later on.