bjoernager/rust
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Rollup merge of #121376 - Nadrieril:mir-half-ranges, r=pnkfelix

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Skip unnecessary comparison with half-open range patterns

This is the last remaining detail in the implementation of half-open range patterns. Until now, a half-open range pattern like `10..` was converted to `10..T::MAX` before lowering to MIR, which generated an extra pointless comparison. With this PR we don't generate it.
This commit is contained in:
Guillaume Gomez 2024-02-29 17:08:37 +01:00 • committed by GitHub
commit 2e0a26a32a
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2 changed files with 33 additions and 39 deletions
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54
compiler/rustc_mir_build/src/build/matches/test.rs
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@ -291,33 +291,41 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
}
TestKind::Range(ref range) => {
let lower_bound_success = self.cfg.start_new_block();
// Test `val` by computing `lo <= val && val <= hi`, using primitive comparisons.
// FIXME: skip useless comparison when the range is half-open.
let lo = range.lo.to_const(range.ty, self.tcx);
let hi = range.hi.to_const(range.ty, self.tcx);
let lo = self.literal_operand(test.span, lo);
let hi = self.literal_operand(test.span, hi);
let val = Operand::Copy(place);
let [success, fail] = *target_blocks else {
bug!("`TestKind::Range` should have two target blocks");
};
self.compare(
block,
lower_bound_success,
fail,
source_info,
BinOp::Le,
lo,
val.clone(),
);
let op = match range.end {
RangeEnd::Included => BinOp::Le,
RangeEnd::Excluded => BinOp::Lt,
// Test `val` by computing `lo <= val && val <= hi`, using primitive comparisons.
let val = Operand::Copy(place);
let intermediate_block = if !range.lo.is_finite() {
block
} else if !range.hi.is_finite() {
success
} else {
self.cfg.start_new_block()
};
self.compare(lower_bound_success, success, fail, source_info, op, val, hi);
if let Some(lo) = range.lo.as_finite() {
let lo = self.literal_operand(test.span, lo);
self.compare(
block,
intermediate_block,
fail,
source_info,
BinOp::Le,
lo,
val.clone(),
);
};
if let Some(hi) = range.hi.as_finite() {
let hi = self.literal_operand(test.span, hi);
let op = match range.end {
RangeEnd::Included => BinOp::Le,
RangeEnd::Excluded => BinOp::Lt,
};
self.compare(intermediate_block, success, fail, source_info, op, val, hi);
}
}
TestKind::Len { len, op } => {