[i386/debug] Fix insn prefix in tls_global_dynamic_64_<mode>

2018-06-25  Tom de Vries  <tdevries@suse.de>

	PR debug/86257
	* config/i386/i386.md (define_insn "*tls_global_dynamic_64_<mode>"):
	Use data16 instead of .byte for insn prefix.

	* gcc.target/i386/pr86257.c: New test.

From-SVN: r262006

gcc/ChangeLog

+2018-06-25  Tom de Vries  <tdevries@suse.de>
+
+	PR debug/86257
+	* config/i386/i386.md (define_insn "*tls_global_dynamic_64_<mode>"):
+	Use data16 instead of .byte for insn prefix.
+
 2018-06-25  Andreas Krebbel  <krebbel@linux.ibm.com>
 
 	PR C++/86082

gcc/config/i386/i386.md

@@ -14733,7 +14733,18 @@
   "TARGET_64BIT"
 {
   if (!TARGET_X32)
-    fputs (ASM_BYTE "0x66\n", asm_out_file);
+    /* The .loc directive has effect for 'the immediately following assembly
+       instruction'.  So for a sequence:
+         .loc f l
+         .byte x
+         insn1
+       the 'immediately following assembly instruction' is insn1.
+       We want to emit an insn prefix here, but if we use .byte (as shown in
+       'ELF Handling For Thread-Local Storage'), a preceding .loc will point
+       inside the insn sequence, rather than to the start.  After relaxation
+       of the sequence by the linker, the .loc might point inside an insn.
+       Use data16 prefix instead, which doesn't have this problem.  */
+    fputs ("\tdata16", asm_out_file);
   output_asm_insn
     ("lea{q}\t{%E1@tlsgd(%%rip), %%rdi|rdi, %E1@tlsgd[rip]}", operands);
   if (TARGET_SUN_TLS || flag_plt || !HAVE_AS_IX86_TLS_GET_ADDR_GOT)

gcc/testsuite/ChangeLog

+2018-06-25  Tom de Vries  <tdevries@suse.de>
+
+	PR debug/86257
+	* gcc.target/i386/pr86257.c: New test.
+
 2018-06-25  Andreas Krebbel  <krebbel@linux.ibm.com>
 
 	PR C++/86082

gcc/testsuite/gcc.target/i386/pr86257.c

+/* { dg-require-effective-target fpic } */
+/* { dg-require-effective-target tls } */
+/* { dg-options "-g -fPIC" } */
+
+__thread int i;
+
+void
+foo(void)
+{
+  i = 0;
+}
+
+/* { dg-final { scan-assembler "data16\[ \t\]*leaq" } } */
+/* { dg-final { scan-assembler-not "\.byte\[ \t\]*0x66\n\[ \t\]*leaq" } } */