[LLVMdev] Suggestions for optimizations

[husar at codasip.com]

Hello!

   I was trying to optimize our automatically generated backend for Open  
RISC and for this purpose I went through the
gcc torture testsuite.
   There are many programs that are better optimized by LLVM, but some are  
much better optimized by gcc 4.9.
The main limitations were is loop unrolling and structures handling.
   Differences can be best seen e.g. when compiling for an architecture  
such as MIPS, or by simply comparing the optimized LLVM IR
with code generated by gcc for MIPS. The tests with the most significant  
difference are listed here:

* loop unrolling

20000422-1.c
20000412-6.c
20050224-1.c
20000412-4.c
20100416-1.c
950714-1.c
pending-4.c

* structures

20010910-1.c (with LLVM from svn, this is even worse than LLVM 3.4)
20020206-2.c
20020402-2.c

* local arrays access

930526-1.c
pr32500.c

* merging same calls to one function to improve code size when optimized

931004-11.c

* better default inlining (probably)

pr19005.c

* other

pr46019.c
pr46909-1.c


   We will try to improve some of these optimizations by ourselves, but I  
do not know when will we get to it, so I am posing it here,
so someone who would be interested in it can take a look at it.

Best regards
   Adam Husar

P.S.:  Also, if someone would be interested in our automatically generated  
LLVM backend, you can contact me,
or you can find additional details at www.codasip.com. We also provide a  
free academical license.