[LICM] Support hoisting of non-argmemonly readonly calls #144497
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The code checking whether a readonly call is safe to hoist is currently limited to only argmemonly calls. However, the actual implementation of does not depend on this in anyway. It either does an MSSA clobber walk on the memory access (which will take all locations accessed by the call into account), or it will look at all MemoryDefs in an entirely location-independent manner. The current restriction dates back to the time when LICM still supported AST, in which case this code *did* reason about the individual pointer arguments.
nikic
commented
Jun 17, 2025
| @@ -153,6 +153,6 @@ else: ; preds = %postinvoke | |||
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| declare void @may_throw() | |||
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| declare i32 @pure_computation() nounwind argmemonly readonly willreturn | |||
| declare i32 @pure_computation() nounwind willreturn memory(none) | |||
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argmemonly for a function without arguments is memory(none). Not LICM's job to figure that out...
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The code checking whether a readonly call is safe to hoist is
currently limited to only argmemonly calls. However, the actual
implementation does not depend on this in any way. It either
does an MSSA clobber walk on the memory access (which will take
all locations accessed by the call into account), or it will
look at all MemoryDefs in an entirely location-independent manner.
The current restriction dates back to the time when LICM still
supported AST, in which case this code did reason about the
individual pointer arguments.