Auto merge of #27252 - tbu-:pr_less_transmutes, r=alexcrichton

The replacements are functions that usually use a single `mem::transmute` in their body and restrict input and output via more concrete types than `T` and `U`. Worth noting are the `transmute` functions for slices and the `from_utf8*` family for mutable slices. Additionally, `mem::transmute` was often used for casting raw pointers, when you can already cast raw pointers just fine with `as`.

This builds upon #27233.

1 files changed, 1 insertions, 2 deletions

diff --git a/src/libstd/sys/unix/backtrace.rs b/src/libstd/sys/unix/backtrace.rs
index ae8bfb07aaf..4128431ee64 100644
--- a/src/libstd/sys/unix/backtrace.rs
+++ b/src/libstd/sys/unix/backtrace.rs
@@ -90,7 +90,6 @@ use io::prelude::*;
 use ffi::CStr;
 use io;
 use libc;
-use mem;
 use str;
 use sync::StaticMutex;
 
@@ -168,7 +167,7 @@ pub fn write(w: &mut Write) -> io::Result<()> {
 
     extern fn trace_fn(ctx: *mut uw::_Unwind_Context,
                        arg: *mut libc::c_void) -> uw::_Unwind_Reason_Code {
-        let cx: &mut Context = unsafe { mem::transmute(arg) };
+        let cx: &mut Context = unsafe { &mut *(arg as *mut Context) };
         let mut ip_before_insn = 0;
         let mut ip = unsafe {
             uw::_Unwind_GetIPInfo(ctx, &mut ip_before_insn) as *mut libc::c_void