clang support gnu asm goto.

Syntax:
  asm [volatile] goto ( AssemblerTemplate
                      :
                      : InputOperands
                      : Clobbers
                      : GotoLabels)

https://gcc.gnu.org/onlinedocs/gcc/Extended-Asm.html

New llvm IR is "callbr" for inline asm goto instead "call" for inline asm
For:
asm goto("testl %0, %0; jne %l1;" :: "r"(cond)::label_true, loop);
IR:
callbr void asm sideeffect "testl $0, $0; jne ${1:l};", "r,X,X,~{dirflag},~{fpsr},~{flags}"(i32 %0, i8* blockaddress(@foo, %label_true), i8* blockaddress(@foo, %loop)) #1
          to label %asm.fallthrough [label %label_true, label %loop], !srcloc !3

asm.fallthrough:                                

Compiler need to generate:
1> a dummy constarint 'X' for each label.
2> an unique fallthrough label for each asm goto stmt " asm.fallthrough%number".


Diagnostic 
1>	duplicate asm operand name are used in output, input and label.
2>	goto out of scope.

llvm-svn: 362045

1 files changed, 3 insertions, 1 deletions

diff --git a/clang/test/Coverage/c-language-features.inc b/clang/test/Coverage/c-language-features.inc
index 356687907d9..ea3b96f6005 100644
--- a/clang/test/Coverage/c-language-features.inc
+++ b/clang/test/Coverage/c-language-features.inc
@@ -71,7 +71,9 @@ theif:
   }
 
   asm ("nop");
-
+  int cond;
+  asm goto("testl %0, %0; jne %l1;" :: "r"(cond)::label_true);
+label_true:
   return;
 }