Auto merge of #97936 - nnethercote:compile-unicode_normalization-faster, r=oli-obk

Compile `unicode-normalization` faster

Various optimizations and cleanups aimed at improving compilation of `unicode-normalization`, which is notable for having several very large `match`es with many char ranges.

Best reviewed one commit at a time.

r? `@oli-obk`

4 files changed, 87 insertions, 115 deletions

diff --git a/compiler/rustc_mir_build/src/build/matches/simplify.rs b/compiler/rustc_mir_build/src/build/matches/simplify.rs
index b4a0c965d6b..c6298904140 100644
--- a/compiler/rustc_mir_build/src/build/matches/simplify.rs
+++ b/compiler/rustc_mir_build/src/build/matches/simplify.rs
@@ -227,15 +227,18 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
                     _ => (None, 0),
                 };
                 if let Some((min, max, sz)) = range {
-                    if let (Some(lo), Some(hi)) = (lo.try_to_bits(sz), hi.try_to_bits(sz)) {
-                        // We want to compare ranges numerically, but the order of the bitwise
-                        // representation of signed integers does not match their numeric order.
-                        // Thus, to correct the ordering, we need to shift the range of signed
-                        // integers to correct the comparison. This is achieved by XORing with a
-                        // bias (see pattern/_match.rs for another pertinent example of this
-                        // pattern).
-                        let (lo, hi) = (lo ^ bias, hi ^ bias);
-                        if lo <= min && (hi > max || hi == max && end == RangeEnd::Included) {
+                    // We want to compare ranges numerically, but the order of the bitwise
+                    // representation of signed integers does not match their numeric order. Thus,
+                    // to correct the ordering, we need to shift the range of signed integers to
+                    // correct the comparison. This is achieved by XORing with a bias (see
+                    // pattern/_match.rs for another pertinent example of this pattern).
+                    //
+                    // Also, for performance, it's important to only do the second `try_to_bits` if
+                    // necessary.
+                    let lo = lo.try_to_bits(sz).unwrap() ^ bias;
+                    if lo <= min {
+                        let hi = hi.try_to_bits(sz).unwrap() ^ bias;
+                        if hi > max || hi == max && end == RangeEnd::Included {
                             // Irrefutable pattern match.
                             return Ok(());
                         }
diff --git a/compiler/rustc_mir_build/src/build/matches/test.rs b/compiler/rustc_mir_build/src/build/matches/test.rs
index 3774a395035..598da80c574 100644
--- a/compiler/rustc_mir_build/src/build/matches/test.rs
+++ b/compiler/rustc_mir_build/src/build/matches/test.rs
@@ -632,39 +632,30 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
             }
 
             (&TestKind::Range(test), &PatKind::Range(pat)) => {
+                use std::cmp::Ordering::*;
+
                 if test == pat {
                     self.candidate_without_match_pair(match_pair_index, candidate);
                     return Some(0);
                 }
 
-                let no_overlap = (|| {
-                    use rustc_hir::RangeEnd::*;
-                    use std::cmp::Ordering::*;
-
-                    let tcx = self.tcx;
-
-                    let test_ty = test.lo.ty();
-                    let lo = compare_const_vals(tcx, test.lo, pat.hi, self.param_env, test_ty)?;
-                    let hi = compare_const_vals(tcx, test.hi, pat.lo, self.param_env, test_ty)?;
-
-                    match (test.end, pat.end, lo, hi) {
-                        // pat < test
-                        (_, _, Greater, _) |
-                        (_, Excluded, Equal, _) |
-                        // pat > test
-                        (_, _, _, Less) |
-                        (Excluded, _, _, Equal) => Some(true),
-                        _ => Some(false),
-                    }
-                })();
-
-                if let Some(true) = no_overlap {
-                    // Testing range does not overlap with pattern range,
-                    // so the pattern can be matched only if this test fails.
+                // For performance, it's important to only do the second
+                // `compare_const_vals` if necessary.
+                let no_overlap = if matches!(
+                    (compare_const_vals(self.tcx, test.hi, pat.lo, self.param_env)?, test.end),
+                    (Less, _) | (Equal, RangeEnd::Excluded) // test < pat
+                ) || matches!(
+                    (compare_const_vals(self.tcx, test.lo, pat.hi, self.param_env)?, pat.end),
+                    (Greater, _) | (Equal, RangeEnd::Excluded) // test > pat
+                ) {
                     Some(1)
                 } else {
                     None
-                }
+                };
+
+                // If the testing range does not overlap with pattern range,
+                // the pattern can be matched only if this test fails.
+                no_overlap
             }
 
             (&TestKind::Range(range), &PatKind::Constant { value }) => {
@@ -768,15 +759,15 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
     ) -> Option<bool> {
         use std::cmp::Ordering::*;
 
-        let tcx = self.tcx;
-
-        let a = compare_const_vals(tcx, range.lo, value, self.param_env, range.lo.ty())?;
-        let b = compare_const_vals(tcx, value, range.hi, self.param_env, range.lo.ty())?;
-
-        match (b, range.end) {
-            (Less, _) | (Equal, RangeEnd::Included) if a != Greater => Some(true),
-            _ => Some(false),
-        }
+        // For performance, it's important to only do the second
+        // `compare_const_vals` if necessary.
+        Some(
+            matches!(compare_const_vals(self.tcx, range.lo, value, self.param_env)?, Less | Equal)
+                && matches!(
+                    (compare_const_vals(self.tcx, value, range.hi, self.param_env)?, range.end),
+                    (Less, _) | (Equal, RangeEnd::Included)
+                ),
+        )
     }
 
     fn values_not_contained_in_range(
diff --git a/compiler/rustc_mir_build/src/thir/pattern/deconstruct_pat.rs b/compiler/rustc_mir_build/src/thir/pattern/deconstruct_pat.rs
index 26532ae33d0..60db98073a3 100644
--- a/compiler/rustc_mir_build/src/thir/pattern/deconstruct_pat.rs
+++ b/compiler/rustc_mir_build/src/thir/pattern/deconstruct_pat.rs
@@ -828,14 +828,8 @@ impl<'tcx> Constructor<'tcx> {
                 FloatRange(other_from, other_to, other_end),
             ) => {
                 match (
-                    compare_const_vals(pcx.cx.tcx, *self_to, *other_to, pcx.cx.param_env, pcx.ty),
-                    compare_const_vals(
-                        pcx.cx.tcx,
-                        *self_from,
-                        *other_from,
-                        pcx.cx.param_env,
-                        pcx.ty,
-                    ),
+                    compare_const_vals(pcx.cx.tcx, *self_to, *other_to, pcx.cx.param_env),
+                    compare_const_vals(pcx.cx.tcx, *self_from, *other_from, pcx.cx.param_env),
                 ) {
                     (Some(to), Some(from)) => {
                         (from == Ordering::Greater || from == Ordering::Equal)
@@ -848,16 +842,7 @@ impl<'tcx> Constructor<'tcx> {
             (Str(self_val), Str(other_val)) => {
                 // FIXME Once valtrees are available we can directly use the bytes
                 // in the `Str` variant of the valtree for the comparison here.
-                match compare_const_vals(
-                    pcx.cx.tcx,
-                    *self_val,
-                    *other_val,
-                    pcx.cx.param_env,
-                    pcx.ty,
-                ) {
-                    Some(comparison) => comparison == Ordering::Equal,
-                    None => false,
-                }
+                self_val == other_val
             }
             (Slice(self_slice), Slice(other_slice)) => self_slice.is_covered_by(*other_slice),
 
diff --git a/compiler/rustc_mir_build/src/thir/pattern/mod.rs b/compiler/rustc_mir_build/src/thir/pattern/mod.rs
index f5d957e30ff..a13748a2d47 100644
--- a/compiler/rustc_mir_build/src/thir/pattern/mod.rs
+++ b/compiler/rustc_mir_build/src/thir/pattern/mod.rs
@@ -15,8 +15,9 @@ use rustc_hir::def::{CtorOf, DefKind, Res};
 use rustc_hir::pat_util::EnumerateAndAdjustIterator;
 use rustc_hir::RangeEnd;
 use rustc_index::vec::Idx;
-use rustc_middle::mir::interpret::{get_slice_bytes, ConstValue};
-use rustc_middle::mir::interpret::{ErrorHandled, LitToConstError, LitToConstInput};
+use rustc_middle::mir::interpret::{
+    ConstValue, ErrorHandled, LitToConstError, LitToConstInput, Scalar,
+};
 use rustc_middle::mir::{self, UserTypeProjection};
 use rustc_middle::mir::{BorrowKind, Field, Mutability};
 use rustc_middle::thir::{Ascription, BindingMode, FieldPat, LocalVarId, Pat, PatKind, PatRange};
@@ -129,7 +130,7 @@ impl<'a, 'tcx> PatCtxt<'a, 'tcx> {
     ) -> PatKind<'tcx> {
         assert_eq!(lo.ty(), ty);
         assert_eq!(hi.ty(), ty);
-        let cmp = compare_const_vals(self.tcx, lo, hi, self.param_env, ty);
+        let cmp = compare_const_vals(self.tcx, lo, hi, self.param_env);
         match (end, cmp) {
             // `x..y` where `x < y`.
             // Non-empty because the range includes at least `x`.
@@ -753,57 +754,49 @@ pub(crate) fn compare_const_vals<'tcx>(
     a: mir::ConstantKind<'tcx>,
     b: mir::ConstantKind<'tcx>,
     param_env: ty::ParamEnv<'tcx>,
-    ty: Ty<'tcx>,
 ) -> Option<Ordering> {
-    let from_bool = |v: bool| v.then_some(Ordering::Equal);
-
-    let fallback = || from_bool(a == b);
-
-    // Use the fallback if any type differs
-    if a.ty() != b.ty() || a.ty() != ty {
-        return fallback();
-    }
-
-    if a == b {
-        return from_bool(true);
-    }
-
-    let a_bits = a.try_eval_bits(tcx, param_env, ty);
-    let b_bits = b.try_eval_bits(tcx, param_env, ty);
-
-    if let (Some(a), Some(b)) = (a_bits, b_bits) {
-        use rustc_apfloat::Float;
-        return match *ty.kind() {
-            ty::Float(ty::FloatTy::F32) => {
-                let l = rustc_apfloat::ieee::Single::from_bits(a);
-                let r = rustc_apfloat::ieee::Single::from_bits(b);
-                l.partial_cmp(&r)
-            }
-            ty::Float(ty::FloatTy::F64) => {
-                let l = rustc_apfloat::ieee::Double::from_bits(a);
-                let r = rustc_apfloat::ieee::Double::from_bits(b);
-                l.partial_cmp(&r)
-            }
-            ty::Int(ity) => {
-                use rustc_middle::ty::layout::IntegerExt;
-                let size = rustc_target::abi::Integer::from_int_ty(&tcx, ity).size();
-                let a = size.sign_extend(a);
-                let b = size.sign_extend(b);
-                Some((a as i128).cmp(&(b as i128)))
-            }
-            _ => Some(a.cmp(&b)),
-        };
-    }
-
-    if let ty::Str = ty.kind() && let (
-        Some(a_val @ ConstValue::Slice { .. }),
-        Some(b_val @ ConstValue::Slice { .. }),
-    ) = (a.try_to_value(tcx), b.try_to_value(tcx))
-    {
-        let a_bytes = get_slice_bytes(&tcx, a_val);
-        let b_bytes = get_slice_bytes(&tcx, b_val);
-        return from_bool(a_bytes == b_bytes);
+    assert_eq!(a.ty(), b.ty());
+
+    let ty = a.ty();
+
+    // This code is hot when compiling matches with many ranges. So we
+    // special-case extraction of evaluated scalars for speed, for types where
+    // raw data comparisons are appropriate. E.g. `unicode-normalization` has
+    // many ranges such as '\u{037A}'..='\u{037F}', and chars can be compared
+    // in this way.
+    match ty.kind() {
+        ty::Float(_) | ty::Int(_) => {} // require special handling, see below
+        _ => match (a, b) {
+            (
+                mir::ConstantKind::Val(ConstValue::Scalar(Scalar::Int(a)), _a_ty),
+                mir::ConstantKind::Val(ConstValue::Scalar(Scalar::Int(b)), _b_ty),
+            ) => return Some(a.cmp(&b)),
+            _ => {}
+        },
+    }
+
+    let a = a.eval_bits(tcx, param_env, ty);
+    let b = b.eval_bits(tcx, param_env, ty);
+
+    use rustc_apfloat::Float;
+    match *ty.kind() {
+        ty::Float(ty::FloatTy::F32) => {
+            let a = rustc_apfloat::ieee::Single::from_bits(a);
+            let b = rustc_apfloat::ieee::Single::from_bits(b);
+            a.partial_cmp(&b)
+        }
+        ty::Float(ty::FloatTy::F64) => {
+            let a = rustc_apfloat::ieee::Double::from_bits(a);
+            let b = rustc_apfloat::ieee::Double::from_bits(b);
+            a.partial_cmp(&b)
+        }
+        ty::Int(ity) => {
+            use rustc_middle::ty::layout::IntegerExt;
+            let size = rustc_target::abi::Integer::from_int_ty(&tcx, ity).size();
+            let a = size.sign_extend(a);
+            let b = size.sign_extend(b);
+            Some((a as i128).cmp(&(b as i128)))
+        }
+        _ => Some(a.cmp(&b)),
     }
-
-    fallback()
 }