Combine four insns
Chris Lattner
clattner@apple.com
Fri Aug 6 21:11:00 GMT 2010
On Aug 6, 2010, at 11:56 AM, Vladimir N. Makarov wrote:
>
> In any case I'd not expect, from a new code selection pass, big code or compile time improvements (e.g. code selection in LLVM is very expensive and takes more time than GCC combiner). But a new code selection pass could be more readable and easy for maintenance.
I agree with you that it is reasonably expensive, but FYI, the selection dag time in LLVM doesn't correspond to combine times. The SelectionDAG phases in LLVM (which does do dag-based, not tree-based, pattern matching) does lowering, matching, pre-regalloc scheduling, and optimization. It's more fair to compare it to expand, combine, pre-ra scheduling, and whatever optimization passes gcc runs early in the rtl pipeline.
-Chris
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