Auto merge of rust-lang#56810 - sinkuu:build_match, r=oli-obk

Improve MIR match generation for ranges

Improves MIR match generation to rule out ranges/values distinct from the range that has been tested. e.g., for this code:

```rust
match x {
    0..=5 if b => 0,
    6..=10 => 1,
    _ => 2,
}
```

MIR (before):

```rust
bb0: { ...; _4 = Le(const 0i32, _1); switchInt(move _4) -> [false: bb6, otherwise: bb5]; }
bb1: { _3 = const 0i32; goto -> bb8; }
bb2: { _6 = _2; switchInt(move _6) -> [false: bb6, otherwise: bb1]; } // If `!b`, jumps to test if `6 <= x <= 10`.
bb3: { _3 = const 1i32; goto -> bb8; }
bb4: { _3 = const 2i32; goto -> bb8; }
bb5: { _5 = Le(_1, const 5i32); switchInt(move _5) -> [false: bb6, otherwise: bb2]; }
bb6: { _7 = Le(const 6i32, _1); switchInt(move _7) -> [false: bb4, otherwise: bb7]; }
bb7: { _8 = Le(_1, const 10i32); switchInt(move _8) -> [false: bb4, otherwise: bb3]; }
```

MIR (after):
```rust
bb0: { ...; _4 = Le(const 0i32, _1); switchInt(move _4) -> [false: bb5, otherwise: bb6]; }
bb1: { _3 = const 0i32; goto -> bb8; }
bb2: { _6 = _2; switchInt(move _6) -> [false: bb4, otherwise: bb1]; } // If `!b`, jumps to `_ =>` arm.
bb3: { _3 = const 1i32; goto -> bb8; }
bb4: { _3 = const 2i32; goto -> bb8; }
bb5: { _7 = Le(const 6i32, _1); switchInt(move _7) -> [false: bb4, otherwise: bb7]; }
bb6: { _5 = Le(_1, const 5i32); switchInt(move _5) -> [false: bb5, otherwise: bb2]; }
bb7: { _8 = Le(_1, const 10i32); switchInt(move _8) -> [false: bb4, otherwise: bb3]; }
```

cc rust-lang#29623

Author: bors

src/librustc_mir/build/matches/mod.rs

@@ -19,7 +19,6 @@ use build::{BlockAnd, BlockAndExtension, Builder};
 use build::{GuardFrame, GuardFrameLocal, LocalsForNode};
 use hair::*;
 use hair::pattern::PatternTypeProjections;
-use rustc::hir;
 use rustc::mir::*;
 use rustc::ty::{self, Ty};
 use rustc::ty::layout::VariantIdx;
@@ -100,7 +99,7 @@ impl<'a, 'gcx, 'tcx> Builder<'a, 'gcx, 'tcx> {
             .collect();
 
         // create binding start block for link them by false edges
-        let candidate_count = arms.iter().fold(0, |ac, c| ac + c.patterns.len());
+        let candidate_count = arms.iter().map(|c| c.patterns.len()).sum::<usize>();
         let pre_binding_blocks: Vec<_> = (0..=candidate_count)
             .map(|_| self.cfg.start_new_block())
             .collect();
@@ -337,7 +336,7 @@ impl<'a, 'gcx, 'tcx> Builder<'a, 'gcx, 'tcx> {
 
     pub fn place_into_pattern(
         &mut self,
-        mut block: BasicBlock,
+        block: BasicBlock,
         irrefutable_pat: Pattern<'tcx>,
         initializer: &Place<'tcx>,
         set_match_place: bool,
@@ -359,7 +358,7 @@ impl<'a, 'gcx, 'tcx> Builder<'a, 'gcx, 'tcx> {
 
         // Simplify the candidate. Since the pattern is irrefutable, this should
         // always convert all match-pairs into bindings.
-        unpack!(block = self.simplify_candidate(block, &mut candidate));
+        self.simplify_candidate(&mut candidate);
 
         if !candidate.match_pairs.is_empty() {
             span_bug!(
@@ -681,12 +680,7 @@ enum TestKind<'tcx> {
     },
 
     // test whether the value falls within an inclusive or exclusive range
-    Range {
-        lo: &'tcx ty::Const<'tcx>,
-        hi: &'tcx ty::Const<'tcx>,
-        ty: Ty<'tcx>,
-        end: hir::RangeEnd,
-    },
+    Range(PatternRange<'tcx>),
 
     // test length of the slice is equal to len
     Len {
@@ -745,7 +739,7 @@ impl<'a, 'gcx, 'tcx> Builder<'a, 'gcx, 'tcx> {
         // complete, all the match pairs which remain require some
         // form of test, whether it be a switch or pattern comparison.
         for candidate in &mut candidates {
-            unpack!(block = self.simplify_candidate(block, candidate));
+            self.simplify_candidate(candidate);
         }
 
         // The candidates are sorted by priority. Check to see
@@ -1035,7 +1029,7 @@ impl<'a, 'gcx, 'tcx> Builder<'a, 'gcx, 'tcx> {
             test, match_pair
         );
         let target_blocks = self.perform_test(block, &match_pair.place, &test);
-        let mut target_candidates: Vec<_> = (0..target_blocks.len()).map(|_| vec![]).collect();
+        let mut target_candidates = vec![vec![]; target_blocks.len()];
 
         // Sort the candidates into the appropriate vector in
         // `target_candidates`. Note that at some point we may

src/librustc_mir/build/matches/simplify.rs

@@ -22,10 +22,9 @@
 //! sort of test: for example, testing which variant an enum is, or
 //! testing a value against a constant.
 
-use build::{BlockAnd, BlockAndExtension, Builder};
+use build::Builder;
 use build::matches::{Ascription, Binding, MatchPair, Candidate};
 use hair::*;
-use rustc::mir::*;
 use rustc::ty;
 use rustc::ty::layout::{Integer, IntegerExt, Size};
 use syntax::attr::{SignedInt, UnsignedInt};
@@ -35,24 +34,23 @@ use std::mem;
 
 impl<'a, 'gcx, 'tcx> Builder<'a, 'gcx, 'tcx> {
     pub fn simplify_candidate<'pat>(&mut self,
-                                    block: BasicBlock,
-                                    candidate: &mut Candidate<'pat, 'tcx>)
-                                    -> BlockAnd<()> {
+                                    candidate: &mut Candidate<'pat, 'tcx>) {
         // repeatedly simplify match pairs until fixed point is reached
         loop {
             let match_pairs = mem::replace(&mut candidate.match_pairs, vec![]);
-            let mut progress = match_pairs.len(); // count how many were simplified
+            let mut changed = false;
             for match_pair in match_pairs {
                 match self.simplify_match_pair(match_pair, candidate) {
-                    Ok(()) => {}
+                    Ok(()) => {
+                        changed = true;
+                    }
                     Err(match_pair) => {
                         candidate.match_pairs.push(match_pair);
-                        progress -= 1; // this one was not simplified
                     }
                 }
             }
-            if progress == 0 {
-                return block.unit(); // if we were not able to simplify any, done.
+            if !changed {
+                return; // if we were not able to simplify any, done.
             }
         }
     }
@@ -109,7 +107,7 @@ impl<'a, 'gcx, 'tcx> Builder<'a, 'gcx, 'tcx> {
                 Err(match_pair)
             }
 
-            PatternKind::Range { lo, hi, ty, end } => {
+            PatternKind::Range(PatternRange { lo, hi, ty, end }) => {
                 let range = match ty.sty {
                     ty::Char => {
                         Some(('\u{0000}' as u128, '\u{10FFFF}' as u128, Size::from_bits(32)))

src/librustc_mir/build/matches/test.rs

@@ -18,6 +18,7 @@
 use build::Builder;
 use build::matches::{Candidate, MatchPair, Test, TestKind};
 use hair::*;
+use hair::pattern::compare_const_vals;
 use rustc_data_structures::bit_set::BitSet;
 use rustc_data_structures::fx::FxHashMap;
 use rustc::ty::{self, Ty};
@@ -71,16 +72,11 @@ impl<'a, 'gcx, 'tcx> Builder<'a, 'gcx, 'tcx> {
                 }
             }
 
-            PatternKind::Range { lo, hi, ty, end } => {
-                assert!(ty == match_pair.pattern.ty);
+            PatternKind::Range(range) => {
+                assert!(range.ty == match_pair.pattern.ty);
                 Test {
                     span: match_pair.pattern.span,
-                    kind: TestKind::Range {
-                        lo,
-                        hi,
-                        ty,
-                        end,
-                    },
+                    kind: TestKind::Range(range),
                 }
             }
 
@@ -136,7 +132,11 @@ impl<'a, 'gcx, 'tcx> Builder<'a, 'gcx, 'tcx> {
             PatternKind::Variant { .. } => {
                 panic!("you should have called add_variants_to_switch instead!");
             }
-            PatternKind::Range { .. } |
+            PatternKind::Range(range) => {
+                // Check that none of the switch values are in the range.
+                self.values_not_contained_in_range(range, indices)
+                    .unwrap_or(false)
+            }
             PatternKind::Slice { .. } |
             PatternKind::Array { .. } |
             PatternKind::Wild |
@@ -200,20 +200,18 @@ impl<'a, 'gcx, 'tcx> Builder<'a, 'gcx, 'tcx> {
                 for (idx, discr) in adt_def.discriminants(tcx) {
                     target_blocks.push(if variants.contains(idx) {
                         values.push(discr.val);
-                        targets.push(self.cfg.start_new_block());
-                        *targets.last().unwrap()
+                        let block = self.cfg.start_new_block();
+                        targets.push(block);
+                        block
                     } else {
-                        if otherwise_block.is_none() {
-                            otherwise_block = Some(self.cfg.start_new_block());
-                        }
-                        otherwise_block.unwrap()
+                        *otherwise_block
+                            .get_or_insert_with(|| self.cfg.start_new_block())
                     });
                 }
-                if let Some(otherwise_block) = otherwise_block {
-                    targets.push(otherwise_block);
-                } else {
-                    targets.push(self.unreachable_block());
-                }
+                targets.push(
+                    otherwise_block
+                        .unwrap_or_else(|| self.unreachable_block()),
+                );
                 debug!("num_enum_variants: {}, tested variants: {:?}, variants: {:?}",
                        num_enum_variants, values, variants);
                 let discr_ty = adt_def.repr.discr_type().to_ty(tcx);
@@ -378,7 +376,7 @@ impl<'a, 'gcx, 'tcx> Builder<'a, 'gcx, 'tcx> {
                 }
             }
 
-            TestKind::Range { ref lo, ref hi, ty, ref end } => {
+            TestKind::Range(PatternRange { ref lo, ref hi, ty, ref end }) => {
                 // Test `val` by computing `lo <= val && val <= hi`, using primitive comparisons.
                 let lo = self.literal_operand(test.span, ty.clone(), lo.clone());
                 let hi = self.literal_operand(test.span, ty.clone(), hi.clone());
@@ -490,8 +488,7 @@ impl<'a, 'gcx, 'tcx> Builder<'a, 'gcx, 'tcx> {
         // away.)
         let tested_match_pair = candidate.match_pairs.iter()
                                                      .enumerate()
-                                                     .filter(|&(_, mp)| mp.place == *test_place)
-                                                     .next();
+                                                     .find(|&(_, mp)| mp.place == *test_place);
         let (match_pair_index, match_pair) = match tested_match_pair {
             Some(pair) => pair,
             None => {
@@ -532,6 +529,24 @@ impl<'a, 'gcx, 'tcx> Builder<'a, 'gcx, 'tcx> {
                 resulting_candidates[index].push(new_candidate);
                 true
             }
+
+            (&TestKind::SwitchInt { switch_ty: _, ref options, ref indices },
+             &PatternKind::Range(range)) => {
+                let not_contained = self
+                    .values_not_contained_in_range(range, indices)
+                    .unwrap_or(false);
+
+                if not_contained {
+                    // No switch values are contained in the pattern range,
+                    // so the pattern can be matched only if this test fails.
+                    let otherwise = options.len();
+                    resulting_candidates[otherwise].push(candidate.clone());
+                    true
+                } else {
+                    false
+                }
+            }
+
             (&TestKind::SwitchInt { .. }, _) => false,
 
 
@@ -610,8 +625,63 @@ impl<'a, 'gcx, 'tcx> Builder<'a, 'gcx, 'tcx> {
                 }
             }
 
+            (&TestKind::Range(test),
+             &PatternKind::Range(pat)) => {
+                if test == pat {
+                    resulting_candidates[0]
+                        .push(self.candidate_without_match_pair(
+                            match_pair_index,
+                            candidate,
+                        ));
+                    return true;
+                }
+
+                let no_overlap = (|| {
+                    use std::cmp::Ordering::*;
+                    use rustc::hir::RangeEnd::*;
+
+                    let param_env = ty::ParamEnv::empty().and(test.ty);
+                    let tcx = self.hir.tcx();
+
+                    let lo = compare_const_vals(tcx, test.lo, pat.hi, param_env)?;
+                    let hi = compare_const_vals(tcx, test.hi, pat.lo, param_env)?;
+
+                    match (test.end, pat.end, lo, hi) {
+                        // pat < test
+                        (_, _, Greater, _) |
+                        (_, Excluded, Equal, _) |
+                        // pat > test
+                        (_, _, _, Less) |
+                        (Excluded, _, _, Equal) => Some(true),
+                        _ => Some(false),
+                    }
+                })();
+
+                if no_overlap == Some(true) {
+                    // Testing range does not overlap with pattern range,
+                    // so the pattern can be matched only if this test fails.
+                    resulting_candidates[1].push(candidate.clone());
+                    true
+                } else {
+                    false
+                }
+            }
+
+            (&TestKind::Range(range), &PatternKind::Constant { ref value }) => {
+                if self.const_range_contains(range, value) == Some(false) {
+                    // `value` is not contained in the testing range,
+                    // so `value` can be matched only if this test fails.
+                    resulting_candidates[1].push(candidate.clone());
+                    true
+                } else {
+                    false
+                }
+            }
+
+            (&TestKind::Range { .. }, _) => false,
+
+
             (&TestKind::Eq { .. }, _) |
-            (&TestKind::Range { .. }, _) |
             (&TestKind::Len { .. }, _) => {
                 // These are all binary tests.
                 //
@@ -722,6 +792,40 @@ impl<'a, 'gcx, 'tcx> Builder<'a, 'gcx, 'tcx> {
                   "simplifyable pattern found: {:?}",
                   match_pair.pattern)
     }
+
+    fn const_range_contains(
+        &self,
+        range: PatternRange<'tcx>,
+        value: &'tcx ty::Const<'tcx>,
+    ) -> Option<bool> {
+        use std::cmp::Ordering::*;
+
+        let param_env = ty::ParamEnv::empty().and(range.ty);
+        let tcx = self.hir.tcx();
+
+        let a = compare_const_vals(tcx, range.lo, value, param_env)?;
+        let b = compare_const_vals(tcx, value, range.hi, param_env)?;
+
+        match (b, range.end) {
+            (Less, _) |
+            (Equal, RangeEnd::Included) if a != Greater => Some(true),
+            _ => Some(false),
+        }
+    }
+
+    fn values_not_contained_in_range(
+        &self,
+        range: PatternRange<'tcx>,
+        indices: &FxHashMap<&'tcx ty::Const<'tcx>, usize>,
+    ) -> Option<bool> {
+        for val in indices.keys() {
+            if self.const_range_contains(range, val)? {
+                return Some(false);
+            }
+        }
+
+        Some(true)
+    }
 }
 
 fn is_switch_ty<'tcx>(ty: Ty<'tcx>) -> bool {

src/librustc_mir/hair/mod.rs

@@ -29,7 +29,7 @@ pub mod cx;
 mod constant;
 
 pub mod pattern;
-pub use self::pattern::{BindingMode, Pattern, PatternKind, FieldPattern};
+pub use self::pattern::{BindingMode, Pattern, PatternKind, PatternRange, FieldPattern};
 pub(crate) use self::pattern::{PatternTypeProjection, PatternTypeProjections};
 
 mod util;