Inline and remove constructor_intersects_pattern().

This is a 2% instruction count win on `unicode_normalization-check-clean`.

Author: nnethercote

src/librustc_mir/hair/pattern/_match.rs

@@ -1625,36 +1625,6 @@ fn split_grouped_constructors<'p, 'tcx>(
     split_ctors
 }
 
-/// Checks whether there exists any shared value in either `ctor` or `pat` by intersecting them.
-fn constructor_intersects_pattern<'p, 'tcx>(
-    tcx: TyCtxt<'tcx>,
-    param_env: ty::ParamEnv<'tcx>,
-    ctor: &Constructor<'tcx>,
-    pat: &'p Pat<'tcx>,
-) -> Option<SmallVec<[&'p Pat<'tcx>; 2]>> {
-    if should_treat_range_exhaustively(tcx, ctor) {
-        match (IntRange::from_ctor(tcx, param_env, ctor), IntRange::from_pat(tcx, param_env, pat)) {
-            (Some(ctor), Some(pat)) => {
-                ctor.intersection(&pat).map(|_| {
-                    let (pat_lo, pat_hi) = pat.range.into_inner();
-                    let (ctor_lo, ctor_hi) = ctor.range.into_inner();
-                    assert!(pat_lo <= ctor_lo && ctor_hi <= pat_hi);
-                    smallvec![]
-                })
-            }
-            _ => None,
-        }
-    } else {
-        // Fallback for non-ranges and ranges that involve floating-point numbers, which are not
-        // conveniently handled by `IntRange`. For these cases, the constructor may not be a range
-        // so intersection actually devolves into being covered by the pattern.
-        match constructor_covered_by_range(tcx, param_env, ctor, pat) {
-            Ok(true) => Some(smallvec![]),
-            Ok(false) | Err(ErrorReported) => None,
-        }
-    }
-}
-
 fn constructor_covered_by_range<'tcx>(
     tcx: TyCtxt<'tcx>,
     param_env: ty::ParamEnv<'tcx>,
@@ -1845,9 +1815,32 @@ fn specialize<'p, 'a: 'p, 'tcx>(
         PatKind::Constant { .. } |
         PatKind::Range { .. } => {
             // If the constructor is a:
-            //      Single value: add a row if the pattern contains the constructor.
-            //      Range: add a row if the constructor intersects the pattern.
-            constructor_intersects_pattern(cx.tcx, cx.param_env, constructor, pat)
+            // - Single value: add a row if the pattern contains the constructor.
+            // - Range: add a row if the constructor intersects the pattern.
+            if should_treat_range_exhaustively(cx.tcx, constructor) {
+                match (IntRange::from_ctor(cx.tcx, cx.param_env, constructor),
+                       IntRange::from_pat(cx.tcx, cx.param_env, pat)) {
+                    (Some(ctor), Some(pat)) => {
+                        ctor.intersection(&pat).map(|_| {
+                            let (pat_lo, pat_hi) = pat.range.into_inner();
+                            let (ctor_lo, ctor_hi) = ctor.range.into_inner();
+                            assert!(pat_lo <= ctor_lo && ctor_hi <= pat_hi);
+                            smallvec![]
+                        })
+                    }
+                    _ => None,
+                }
+            } else {
+                // Fallback for non-ranges and ranges that involve
+                // floating-point numbers, which are not conveniently handled
+                // by `IntRange`. For these cases, the constructor may not be a
+                // range so intersection actually devolves into being covered
+                // by the pattern.
+                match constructor_covered_by_range(cx.tcx, cx.param_env, constructor, pat) {
+                    Ok(true) => Some(smallvec![]),
+                    Ok(false) | Err(ErrorReported) => None,
+                }
+            }
         }
 
         PatKind::Array { ref prefix, ref slice, ref suffix } |