On 27-6-2022 04:43, J. Gareth Moreton via fpc-devel wrote:
Hi everyone,
I'm playing around with a peephole optimization (back to my roots!) and
I've come across a relatively simple one that aims to reduce instruction
size occasionally. One part involves reducing the opsize if the
constant is numeric. For example:
testl $17,76(%rcx) -> testb $17,76(%rcx)
Or:
testl $1,%ebx -> testb $1,%bl
Obviously I check to make sure the constant fits into the smaller size.
Is there a time when this is NOT recommended? I'm trying to remember
issues with partial register or memory writes, but in this case, it's
just a partial read.
It's not only the constant size which has to fit, but also the other
operand. So you cannot use it for testing an integer for the value of 1
Marc
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