rtl: ICE with thread_local and inline asm [PR104777]

In r270550, Jakub fixed classify_insn to handle asm goto: if the asm can
jump to a label, the insn should be a JUMP_INSN.

However, as the following testcase shows, non-null ASM_OPERANDS_LABEL_VEC
doesn't guarantee that the rtx has any actual labels it can branch to.
Here, the rtvec has 0 elements because expand_asm_stmt created it:

  rtvec labelvec = rtvec_alloc (nlabels); // nlabels == 0

This causes an ICE in update_br_prob_note: BRANCH_EDGE (bb) crashes
because there's no branch edge.  I think we can fix this by checking
that there is at least one label the asm can jump to before wrapping
the ASM_OPERANDS in a JUMP_INSN.

	PR rtl-optimization/104777

gcc/ChangeLog:

	* rtl.cc (classify_insn): For ASM_OPERANDS, return JUMP_INSN only if
	ASM_OPERANDS_LABEL_VEC has at least one element.

gcc/testsuite/ChangeLog:

	* gcc.dg/torture/tls/pr104777.c: New test.

gcc/rtl.cc

@@ -765,7 +765,7 @@ classify_insn (rtx x)
     return CALL_INSN;
   if (ANY_RETURN_P (x))
     return JUMP_INSN;
-  if (GET_CODE (x) == ASM_OPERANDS && ASM_OPERANDS_LABEL_VEC (x))
+  if (GET_CODE (x) == ASM_OPERANDS && ASM_OPERANDS_LABEL_LENGTH (x))
     return JUMP_INSN;
   if (GET_CODE (x) == SET)
     {
@@ -794,7 +794,7 @@ classify_insn (rtx x)
       if (has_return_p)
 	return JUMP_INSN;
       if (GET_CODE (XVECEXP (x, 0, 0)) == ASM_OPERANDS
-	  && ASM_OPERANDS_LABEL_VEC (XVECEXP (x, 0, 0)))
+	  && ASM_OPERANDS_LABEL_LENGTH (XVECEXP (x, 0, 0)))
 	return JUMP_INSN;
     }
 #ifdef GENERATOR_FILE

gcc/testsuite/gcc.dg/torture/tls/pr104777.c

+/* PR rtl-optimization/104777 */
+/* { dg-do compile } */
+/* { dg-require-effective-target tls } */
+ 
+int savestate_r;
+int savestate_ssb;
+extern void abort();
+__thread int  loop;
+void f (void)
+{
+  int savestate_r0_5;
+  int savestate_r1_6;
+
+  __asm__("" : "=m" (savestate_ssb), "=r" (savestate_r));
+  savestate_r0_5 = savestate_r;
+  if (savestate_r0_5 == 0)
+  {
+    __asm__ __volatile__("" :  : "m" (loop));
+    abort ();
+  }
+
+  __asm__("" : "=m" (savestate_ssb), "=r" (savestate_r));
+  savestate_r1_6 = savestate_r;
+  if (savestate_r1_6 != 0)
+    return;
+
+  __asm__ __volatile__("" :  : "m" (loop));
+  abort ();
+
+}