Improve optimizations for boolean values #15464
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I am not qualified to evaluate this patch, but do you have any benchmarks that demonstrate an improvement? |
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See the test case given in #15203. (I only had the "Fixes" on a commit, added it to the PR description now). Before: After: The relevant optimization here is turning the store loop into a memset. It's not triggered for types which are not a byte-width multiple. |
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| let lltemp = builder.alloca(val_ty(llforeign_arg), ""); | ||
| builder.store(llforeign_arg, lltemp); | ||
| llforeign_arg = lltemp; | ||
| llforeign_arg = if ty::type_is_bool(rust_ty) { |
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Is there a particular reason isn't this using the store_ty abstraction?
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I can't, because this function doesn't use the regular building blocks like Block, but uses a Builder directly.
LLVM doesn't really like types with a bit-width that isn't a multiple of 8 and disable various optimizations if it encounters such types used with loads/stores. OTOH, booleans must be represented as i1 when used as SSA values. To get the best results, we must use i1 for SSA values, and i8 when storing the value to memory. By using range asserts on loads, LLVM can eliminate the required zero-extend and truncate operations. Fixes rust-lang#15203
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Jul 7, 2014
LLVM doesn't handle i1 value in allocas/memory very well and skips a number of optimizations if it hits it. So we have to do the same thing that Clang does, using i1 for SSA values, but storing i8 in memory. Fixes #15203.
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LLVM doesn't handle i1 value in allocas/memory very well and skips a number of optimizations if it hits it. So we have to do the same thing that Clang does, using i1 for SSA values, but storing i8 in memory.
Fixes #15203.