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Re: [RFA][PATCH][PR rtl-optimization/47477] Type narrowing in match.pd

On 02/12/15 00:01, Bin.Cheng wrote:

Cool that we are trying to simplify type conversion using generic
match facility.  I have thought about type promotion in match.pd too.
match.pd really feels like a meta-language which describes how to combine gimple or generic statements.

For example, (unsigned long long)(unsigned long)(int_expr), if we can
prove int_expr is always positive (in my case, this is from vrp
information), then the first conversion can be saved.  This is another
way for (and related? I didn't look at the code) the sign/zero
extension elimination work using VRP I suppose?
In theory, given VRP information attached to an SSA_NAME you could query that information in the conditional part of the match.pd pattern.

Another patch I'm working on is best described as detecting cases where an outer bit-and masks off all the bits outside the innermost operand's type. Under the right conditions, this also allows for narrowing.


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