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, 45 insertions, 0 deletions

diff --git a/clang/test/Sema/asm-goto.cpp b/clang/test/Sema/asm-goto.cpp
new file mode 100644
index 00000000000..f61a8096b83
--- /dev/null
+++ b/clang/test/Sema/asm-goto.cpp
@@ -0,0 +1,45 @@
+// RUN: %clang_cc1 %s -triple i386-pc-linux-gnu -verify -fsyntax-only
+
+struct NonTrivial {
+  ~NonTrivial();
+  int f(int);
+private:
+  int k;
+};
+void JumpDiagnostics(int n) {
+// expected-error@+1 {{cannot jump from this goto statement to its label}}
+  goto DirectJump;
+// expected-note@+1 {{jump bypasses variable with a non-trivial destructor}}
+  NonTrivial tnp1;
+
+DirectJump:
+// expected-error@+1 {{cannot jump from this asm goto statement to one of its possible targets}}
+  asm goto("jmp %l0;" ::::Later);
+// expected-note@+1 {{jump bypasses variable with a non-trivial destructor}}
+  NonTrivial tnp2;
+// expected-note@+1 {{possible target of asm goto statement}}
+Later:
+  return;
+}
+
+struct S { ~S(); };
+void foo(int a) {
+  if (a) {
+FOO:
+// expected-note@+2 {{jump exits scope of variable with non-trivial destructor}}
+// expected-note@+1 {{jump exits scope of variable with non-trivial destructor}}
+    S s;
+    void *p = &&BAR;
+// expected-error@+1 {{cannot jump from this asm goto statement to one of its possible targets}}
+  asm goto("jmp %l0;" ::::BAR);
+// expected-error@+1 {{cannot jump from this indirect goto statement to one of its possible targets}}
+    goto *p;
+    p = &&FOO;
+    goto *p;
+    return;
+  }
+// expected-note@+2 {{possible target of asm goto statement}}
+// expected-note@+1 {{possible target of indirect goto statement}}
+BAR:
+  return;
+}