Fix handling of large branch values in cranelift_frontend::Switch #8422
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Previously trying to branch on a i128 with a branch value larger than i64::MAX after truncating to u64 would result in the branch value incorrectly getting interpreted as a value with the upper 64 bits being 1 rather than 0.
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| assert!(u64::try_from(y).is_ok()); | ||
| bx.ins().icmp_imm(cond, x, y as i64) |
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This assert/conversion combination is a little surprising. If y converts to u64, doesn't that mean that there's a possibility that it would produce a negative i64 value?
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A negative i64 here is fine as the value on which we are operating is at most a 64bit integer and thus no implicit sign extension of the immediate will be done by icmp_imm.
elliottt
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Apr 21, 2024
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Previously trying to branch on a i128 with a branch value larger than i64::MAX after truncating to u64 would result in the branch value incorrectly getting interpreted as a value with the upper 64 bits being 1 rather than 0.
Fixes rust-lang/rustc_codegen_cranelift#1484