Fix an off-by-two condition in heap legalization#3462
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This commit fixes an issue in Cranelift where legalization of `heap_addr` instructions (used by wasm to represent heap accesses) could be off-by-two where loads that should be valid were actually treated as invalid. The bug here happened in an optimization where tests against odd constants were being altered to tests against even constants by subtracting one from the limit instead of adding one to the limit. The comment around this area has been updated in accordance with a little more math-stuff as well to help future readers.
cfallin
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Thanks very much for tracking this down!
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This commit fixes an issue in Cranelift where legalization of
heap_addrinstructions (used by wasm to represent heap accesses) couldbe off-by-two where loads that should be valid were actually treated as
invalid. The bug here happened in an optimization where tests against
odd constants were being altered to tests against even constants by
subtracting one from the limit instead of adding one to the limit. The
comment around this area has been updated in accordance with a little
more math-stuff as well to help future readers.