[PATCH] Check rtx_costs in combine.c's try_combine
Richard Kenner
kenner@vlsi1.ultra.nyu.edu
Mon Jun 28 13:49:00 GMT 2004
The following patch adds an additional test to combine.c's try_combine
to only allow instructions to be merged/combined if the backend's
TARGET_RTX_COST macro indictates that the replacement is atleast as
cheap as the original. Historically, GCC's "combine" pass has used
a greedy algorithm that always attempts to build complex composite
instructions that are recognized by the back-end independent of any
cost metric. Increasingly with modern processors, the more complex
instructions supported are an ISA are not automatically better than
their component parts.
Yes, but in such a case, those complex instructions should not in the MD
file as there is no situation in which they should be used.
I disagree with this patch.
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