From 2f9a9ed785416a7350f30141fcc405b69a1b9d5d Mon Sep 17 00:00:00 2001
From: John McCall <rjmccall@apple.com>
Date: Mon, 14 Mar 2011 20:01:21 +0000
Subject: [PATCH] Make llvm_unreachable evaluate to __builtin_unreachable() in
 -Asserts builds, which was the apparent consensus of PR8973 and llvmdev.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@127608 91177308-0d34-0410-b5e6-96231b3b80d8
---
 include/llvm/Support/Compiler.h      | 15 +++++++++++++++
 include/llvm/Support/ErrorHandling.h |  2 +-
 2 files changed, 16 insertions(+), 1 deletion(-)

diff --git a/include/llvm/Support/Compiler.h b/include/llvm/Support/Compiler.h
index 67f0fd7e0dc..2d2a0b124ab 100644
--- a/include/llvm/Support/Compiler.h
+++ b/include/llvm/Support/Compiler.h
@@ -126,4 +126,19 @@
   decl
 #endif
 
+// LLVM_BUILTIN_UNREACHABLE - On compilers which support it, expands
+// to an expression which states that it is undefined behavior for the
+// compiler to reach this point.
+#if defined(__clang__) || (__GNUC__ > 4) \
+ || (__GNUC__ == 4 && __GNUC_MINOR__ >= 5)
+# define LLVM_BUILTIN_UNREACHABLE __builtin_unreachable()
+#else
+#ifdef __cplusplus
+extern "C" LLVM_ATTRIBUTE_NORETURN void abort();
+#else
+extern LLVM_ATTRIBUTE_NORETURN void abort();
+#endif
+# define LLVM_BUILTIN_UNREACHABLE abort()
+#endif
+
 #endif
diff --git a/include/llvm/Support/ErrorHandling.h b/include/llvm/Support/ErrorHandling.h
index 5eca438d8b4..fb0c88d8d8d 100644
--- a/include/llvm/Support/ErrorHandling.h
+++ b/include/llvm/Support/ErrorHandling.h
@@ -97,7 +97,7 @@ namespace llvm {
 #define llvm_unreachable(msg) \
   ::llvm::llvm_unreachable_internal(msg, __FILE__, __LINE__)
 #else
-#define llvm_unreachable(msg) ::llvm::llvm_unreachable_internal()
+#define llvm_unreachable(msg) LLVM_BUILTIN_UNREACHABLE
 #endif
 
 #endif