LocalCSE: Do not optimize small things like global.get #6087
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tlively
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Nov 8, 2023
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radekdoulik
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Jul 12, 2024
) LocalCSE is nice for large expressions, but for small things it has always been of unclear benefit since VMs also do GVN/CSE anyhow. So we are likely not speeding anything up, but hopefully we are reducing code size at least. Doing LocalCSE on something small like a global.get is very possibly going to increase code size, however (since we add a tee, and since the local gets are of similar size to global gets - depends on LUB sizes). On real-world Java code that overhead is noticeable, so this PR makes us more careful, and we skip things of size 1 (no children).
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LocalCSE is nice for large expressions, but for small things it has always been of
unclear benefit since VMs also do GVN/CSE anyhow. So we are likely not speeding
anything up, but hopefully we are reducing code size at least. Doing LocalCSE on
something small like a
global.getis very possibly going to increase code size,however (since we add a tee, and since the local gets are of similar size to global
gets - depends on LUB sizes). On real-world Java code that overhead is noticeable,
so this PR makes us more careful, and we skip things of size 1 (no children).