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Additional assumption to elide bounds check

This commit is contained in:
Dániel Buga 2020-08-30 21:26:03 +02:00
parent 85fbf49ce0
commit c88b167f15
1 changed files with 21 additions and 5 deletions
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26
compiler/rustc_codegen_ssa/src/mir/rvalue.rs
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@ -327,13 +327,29 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
if er.end != er.start
&& scalar.valid_range.end() > scalar.valid_range.start()
{
// We want `table[e as usize]` to not
// We want `table[e as usize ± k]` to not
// have bound checks, and this is the most
// convenient place to put the `assume`.
let ll_t_in_const =
// convenient place to put the `assume`s.
if *scalar.valid_range.start() > 0 {
let enum_value_lower_bound = bx
.cx()
.const_uint_big(ll_t_in, *scalar.valid_range.start());
let cmp_start = bx.icmp(
IntPredicate::IntUGE,
llval,
enum_value_lower_bound,
);
bx.assume(cmp_start);
}
let enum_value_upper_bound =
bx.cx().const_uint_big(ll_t_in, *scalar.valid_range.end());
let cmp = bx.icmp(IntPredicate::IntULE, llval, ll_t_in_const);
bx.assume(cmp);
let cmp_end = bx.icmp(
IntPredicate::IntULE,
llval,
enum_value_upper_bound,
);
bx.assume(cmp_end);
}
}
}