[LLVMdev] is it possible to use gcc vectorizer ?

[Duncan Sands]

Hi Kuan-Hsu,

> gcc provides auto-vectorization on the tree-ssa framework, and llvm-gcc
> uses tree-ssa to generate LLVM IR.
> so, is it possible to use gcc vectorizer in LLVM?

in theory yes, but you would have to modify the compiler.  In llvm-gcc all
gcc optimizers are turned off, and this includes the vectorizer (see the
#ifdef ENABLE_LLVM clauses in gcc/passes.c), so you would have to reenable
them.  This might cause problems due to potential bad interactions between
the gcc optimizers and LLVM modifications to the compiler - I don't know.

Ciao,

Duncan.

PS: In case anyone is wondering, this is not possible with the dragonegg
plugin, which is a pity since the auto-vectorizer is much improved in gcc-4.5
I hear.  The reason is that gimple->IR conversion replaces gcc's LTO logic,
and this runs before the auto-vectorizer.