Simplify MIR opt tests

This commit removes many cases of MIR opt tests emitting `.diff`s for more than one pass. These
tests cannot be `unit-test`s, and so they are easy to break, and they also provide little value due
to having excessively strong opinions over *how* a piece of code should be optimized.

Where reasonable, we instead add separate test files that only emit the `PreCodegen.after` MIR for
code where we want to track what the result of the net result of the optimization pipeline's output
is.

1 files changed, 11 insertions, 0 deletions

diff --git a/src/test/mir-opt/lower_array_len_e2e.array_len.PreCodegen.after.mir b/src/test/mir-opt/lower_array_len_e2e.array_len.PreCodegen.after.mir
new file mode 100644
index 00000000000..4b19f679558
--- /dev/null
+++ b/src/test/mir-opt/lower_array_len_e2e.array_len.PreCodegen.after.mir
@@ -0,0 +1,11 @@
+// MIR for `array_len` after PreCodegen
+
+fn array_len(_1: &[u8; N]) -> usize {
+    debug arr => _1;                     // in scope 0 at $DIR/lower_array_len_e2e.rs:+0:34: +0:37
+    let mut _0: usize;                   // return place in scope 0 at $DIR/lower_array_len_e2e.rs:+0:52: +0:57
+
+    bb0: {
+        _0 = const N;                    // scope 0 at $DIR/lower_array_len_e2e.rs:+1:5: +1:14
+        return;                          // scope 0 at $DIR/lower_array_len_e2e.rs:+2:2: +2:2
+    }
+}