Merge commit 'cfe09ed28d8a65b671e8b7a716a933e98e810e32'

Conflicts:
	lib/Target/ARM/ARMFrameLowering.cpp
	lib/Target/Mips/MipsRegisterInfo.cpp
	lib/Target/X86/X86ISelLowering.cpp
	lib/Transforms/IPO/ExtractGV.cpp
	tools/Makefile
	tools/gold/gold-plugin.cpp

The only interesting conflict was X86ISelLowering.ccp, which
meant I had to essentially revert r167104. The problem is that we are
using ESP as the stack pointer in X86ISelLowering and RSP as the
stack pointer in X86FrameLowering, and that revision made them
both consistently use X86RegisterInfo to determine which to use.

1 files changed, 15 insertions, 10 deletions

diff --git a/docs/CodingStandards.rst b/docs/CodingStandards.rst
index 418e3f05a3..90835307b1 100644
--- a/docs/CodingStandards.rst
+++ b/docs/CodingStandards.rst
@@ -862,23 +862,28 @@ Here are more examples:
 
 You get the idea.
 
-Please be aware that, when adding assert statements, not all compilers are aware
-of the semantics of the assert.  In some places, asserts are used to indicate a
-piece of code that should not be reached.  These are typically of the form:
+In the past, asserts were used to indicate a piece of code that should not be
+reached.  These were typically of the form:
 
 .. code-block:: c++
 
-  assert(0 && "Some helpful error message");
+  assert(0 && "Invalid radix for integer literal");
 
-When used in a function that returns a value, they should be followed with a
-return statement and a comment indicating that this line is never reached.  This
-will prevent a compiler which is unable to deduce that the assert statement
-never returns from generating a warning.
+This has a few issues, the main one being that some compilers might not
+understand the assertion, or warn about a missing return in builds where
+assertions are compiled out.
+
+Today, we have something much better: ``llvm_unreachable``:
 
 .. code-block:: c++
 
-  assert(0 && "Some helpful error message");
-  return 0;
+  llvm_unreachable("Invalid radix for integer literal");
+
+When assertions are enabled, this will print the message if it's ever reached
+and then exit the program. When assertions are disabled (i.e. in release
+builds), ``llvm_unreachable`` becomes a hint to compilers to skip generating
+code for this branch. If the compiler does not support this, it will fall back
+to the "abort" implementation.
 
 Another issue is that values used only by assertions will produce an "unused
 value" warning when assertions are disabled.  For example, this code will warn: