Fix some broken links

Author: camelid

src/mir/optimizations.md

@@ -85,7 +85,7 @@ The array is an array of `&dyn MirPass` trait objects. Typically, a pass is
 implemented in its own module of the [`rustc_mir_transform`][trans] crate.
 
 [rop]: https://doc.rust-lang.org/nightly/nightly-rustc/rustc_mir_transform/fn.run_optimization_passes.html
-[`MirPass`]: https://doc.rust-lang.org/nightly/nightly-rustc/rustc_mir_transform/trait.MirPass.html
+[`MirPass`]: https://doc.rust-lang.org/nightly/nightly-rustc/rustc_middle/mir/trait.MirPass.html
 [trans]: https://doc.rust-lang.org/nightly/nightly-rustc/rustc_mir_transform/index.html
 
 Some examples of passes are:
@@ -95,7 +95,7 @@ Some examples of passes are:
 
 You can see the ["Implementors" section of the `MirPass` rustdocs][impl] for more examples.
 
-[impl]: https://doc.rust-lang.org/nightly/nightly-rustc/rustc_mir_transform/trait.MirPass.html#implementors
+[impl]: https://doc.rust-lang.org/nightly/nightly-rustc/rustc_middle/mir/trait.MirPass.html#implementors
 [constprop]: https://en.wikipedia.org/wiki/Constant_folding#Constant_propagation
 
 ## MIR optimization levels

src/profiling.md

@@ -12,7 +12,7 @@ Depending on what you're trying to measure, there are several different approach
 
 - If you want a medium-to-high level overview of where `rustc` is spending its time:
   - The `-Z self-profile` flag and [measureme](https://github.com/rust-lang/measureme) tools offer a query-based approach to profiling.
-    See [their docs](https://github.com/rust-lang/measureme/blob/master/summarize/Readme.md) for more information.
+    See [their docs](https://github.com/rust-lang/measureme/blob/master/summarize/README.md) for more information.
 
 - If you want function level performance data or even just more details than the above approaches:
   - Consider using a native code profiler such as [perf](profiling/with_perf.html)