Try to make Vec benchmarks only run code they are benchmarking

Many of the Vec benchmarks assert what values should be produced by the
benchmarked code. In some cases, these asserts dominate the runtime of
the benchmarks they are in, causing the benchmarks to understate the
impact of an optimization or regression.

1 files changed, 25 insertions, 68 deletions

diff --git a/library/alloc/benches/vec.rs b/library/alloc/benches/vec.rs
index 7a098219ce4..48709e89823 100644
--- a/library/alloc/benches/vec.rs
+++ b/library/alloc/benches/vec.rs
@@ -4,23 +4,13 @@ use test::{black_box, Bencher};
 
 #[bench]
 fn bench_new(b: &mut Bencher) {
-    b.iter(|| {
-        let v: Vec<u32> = Vec::new();
-        assert_eq!(v.len(), 0);
-        assert_eq!(v.capacity(), 0);
-        v
-    })
+    b.iter(|| Vec::<u32>::new())
 }
 
 fn do_bench_with_capacity(b: &mut Bencher, src_len: usize) {
     b.bytes = src_len as u64;
 
-    b.iter(|| {
-        let v: Vec<u32> = Vec::with_capacity(src_len);
-        assert_eq!(v.len(), 0);
-        assert_eq!(v.capacity(), src_len);
-        v
-    })
+    b.iter(|| Vec::<u32>::with_capacity(src_len))
 }
 
 #[bench]
@@ -46,12 +36,7 @@ fn bench_with_capacity_1000(b: &mut Bencher) {
 fn do_bench_from_fn(b: &mut Bencher, src_len: usize) {
     b.bytes = src_len as u64;
 
-    b.iter(|| {
-        let dst = (0..src_len).collect::<Vec<_>>();
-        assert_eq!(dst.len(), src_len);
-        assert!(dst.iter().enumerate().all(|(i, x)| i == *x));
-        dst
-    })
+    b.iter(|| (0..src_len).collect::<Vec<_>>())
 }
 
 #[bench]
@@ -77,12 +62,7 @@ fn bench_from_fn_1000(b: &mut Bencher) {
 fn do_bench_from_elem(b: &mut Bencher, src_len: usize) {
     b.bytes = src_len as u64;
 
-    b.iter(|| {
-        let dst: Vec<usize> = repeat(5).take(src_len).collect();
-        assert_eq!(dst.len(), src_len);
-        assert!(dst.iter().all(|x| *x == 5));
-        dst
-    })
+    b.iter(|| repeat(5).take(src_len).collect::<Vec<usize>>())
 }
 
 #[bench]
@@ -110,12 +90,7 @@ fn do_bench_from_slice(b: &mut Bencher, src_len: usize) {
 
     b.bytes = src_len as u64;
 
-    b.iter(|| {
-        let dst = src.clone()[..].to_vec();
-        assert_eq!(dst.len(), src_len);
-        assert!(dst.iter().enumerate().all(|(i, x)| i == *x));
-        dst
-    });
+    b.iter(|| src.as_slice().to_vec());
 }
 
 #[bench]
@@ -144,9 +119,7 @@ fn do_bench_from_iter(b: &mut Bencher, src_len: usize) {
     b.bytes = src_len as u64;
 
     b.iter(|| {
-        let dst: Vec<_> = FromIterator::from_iter(src.clone());
-        assert_eq!(dst.len(), src_len);
-        assert!(dst.iter().enumerate().all(|(i, x)| i == *x));
+        let dst: Vec<_> = FromIterator::from_iter(src.iter().cloned());
         dst
     });
 }
@@ -180,8 +153,6 @@ fn do_bench_extend(b: &mut Bencher, dst_len: usize, src_len: usize) {
     b.iter(|| {
         let mut dst = dst.clone();
         dst.extend(src.clone());
-        assert_eq!(dst.len(), dst_len + src_len);
-        assert!(dst.iter().enumerate().all(|(i, x)| i == *x));
         dst
     });
 }
@@ -230,8 +201,6 @@ fn do_bench_extend_from_slice(b: &mut Bencher, dst_len: usize, src_len: usize) {
     b.iter(|| {
         let mut dst = dst.clone();
         dst.extend_from_slice(&src);
-        assert_eq!(dst.len(), dst_len + src_len);
-        assert!(dst.iter().enumerate().all(|(i, x)| i == *x));
         dst
     });
 }
@@ -290,12 +259,7 @@ fn do_bench_clone(b: &mut Bencher, src_len: usize) {
 
     b.bytes = src_len as u64;
 
-    b.iter(|| {
-        let dst = src.clone();
-        assert_eq!(dst.len(), src_len);
-        assert!(dst.iter().enumerate().all(|(i, x)| i == *x));
-        dst
-    });
+    b.iter(|| src.clone());
 }
 
 #[bench]
@@ -329,8 +293,7 @@ fn do_bench_clone_from(b: &mut Bencher, times: usize, dst_len: usize, src_len: u
 
         for _ in 0..times {
             dst.clone_from(&src);
-            assert_eq!(dst.len(), src_len);
-            assert!(dst.iter().enumerate().all(|(i, x)| dst_len + i == *x));
+            dst = black_box(dst);
         }
         dst
     });
@@ -463,11 +426,10 @@ macro_rules! bench_in_place {
             fn $fname(b: &mut Bencher) {
                 b.iter(|| {
                     let src: Vec<$type> = black_box(vec![$init; $count]);
-                    let mut sink = src.into_iter()
+                    src.into_iter()
                         .enumerate()
                         .map(|(idx, e)| idx as $type ^ e)
-                        .collect::<Vec<$type>>();
-                    black_box(sink.as_mut_ptr())
+                        .collect::<Vec<$type>>()
                 });
             }
         )+
@@ -527,7 +489,6 @@ fn bench_in_place_zip_recycle(b: &mut Bencher) {
             .enumerate()
             .map(|(i, (d, s))| d.wrapping_add(i as u8) ^ s)
             .collect::<Vec<_>>();
-        assert_eq!(mangled.len(), 1000);
         data = black_box(mangled);
     });
 }
@@ -614,23 +575,6 @@ fn bench_nest_chain_chain_collect(b: &mut Bencher) {
     });
 }
 
-pub fn example_plain_slow(l: &[u32]) -> Vec<u32> {
-    let mut result = Vec::with_capacity(l.len());
-    result.extend(l.iter().rev());
-    result
-}
-
-pub fn map_fast(l: &[(u32, u32)]) -> Vec<u32> {
-    let mut result = Vec::with_capacity(l.len());
-    for i in 0..l.len() {
-        unsafe {
-            *result.get_unchecked_mut(i) = l[i].0;
-            result.set_len(i);
-        }
-    }
-    result
-}
-
 #[bench]
 fn bench_range_map_collect(b: &mut Bencher) {
     b.iter(|| (0..LEN).map(|_| u32::default()).collect::<Vec<_>>());
@@ -669,7 +613,11 @@ fn bench_rev_1(b: &mut Bencher) {
 #[bench]
 fn bench_rev_2(b: &mut Bencher) {
     let data = black_box([0; LEN]);
-    b.iter(|| example_plain_slow(&data));
+    b.iter(|| {
+        let mut v = Vec::<u32>::with_capacity(data.len());
+        v.extend(data.iter().rev());
+        v
+    });
 }
 
 #[bench]
@@ -685,7 +633,16 @@ fn bench_map_regular(b: &mut Bencher) {
 #[bench]
 fn bench_map_fast(b: &mut Bencher) {
     let data = black_box([(0, 0); LEN]);
-    b.iter(|| map_fast(&data));
+    b.iter(|| {
+        let mut result = Vec::with_capacity(data.len());
+        for i in 0..data.len() {
+            unsafe {
+                *result.get_unchecked_mut(i) = data[i].0;
+                result.set_len(i);
+            }
+        }
+        result
+    });
 }
 
 fn random_sorted_fill(mut seed: u32, buf: &mut [u32]) {