x86: introduce a state stack for .arch

When using just slightly non-trivial combinations of .arch, it can be
quite useful to be able to go back to prior state without needing to
re-invoke perhaps many earlier directives and without needing to invoke
perhaps many "negative" ones. Like some other architectures allow
saving (pushing) and restoring (popping) present/prior state.

For now require the same .code<N> to be in effect for ".arch pop" that
was in effect for the corresponding ".arch push".

Also change the global "no_cond_jump_promotion" to be bool, to match the
new struct field.

gas/config/tc-i386.c

@@ -788,7 +788,7 @@ i386_cpu_flags cpu_arch_isa_flags;
 
 /* If set, conditional jumps are not automatically promoted to handle
    larger than a byte offset.  */
-static unsigned int no_cond_jump_promotion = 0;
+static bool no_cond_jump_promotion = false;
 
 /* Encode SSE instructions with VEX prefix.  */
 static unsigned int sse2avx;
@@ -2660,6 +2660,20 @@ extend_cpu_sub_arch_name (const char *name)
 static void
 set_cpu_arch (int dummy ATTRIBUTE_UNUSED)
 {
+  typedef struct arch_stack_entry
+  {
+    const struct arch_stack_entry *prev;
+    const char *name;
+    char *sub_name;
+    i386_cpu_flags flags;
+    i386_cpu_flags isa_flags;
+    enum processor_type isa;
+    enum flag_code flag_code;
+    char stackop_size;
+    bool no_cond_jump_promotion;
+  } arch_stack_entry;
+  static const arch_stack_entry *arch_stack_top;
+
   SKIP_WHITESPACE ();
 
   if (!is_end_of_line[(unsigned char) *input_line_pointer])
@@ -2703,6 +2717,67 @@ set_cpu_arch (int dummy ATTRIBUTE_UNUSED)
 	      j = ARRAY_SIZE (cpu_arch) + 1;
 	    }
 	}
+      else if (strcmp (string, "push") == 0)
+	{
+	  arch_stack_entry *top = XNEW (arch_stack_entry);
+
+	  top->name = cpu_arch_name;
+	  if (cpu_sub_arch_name)
+	    top->sub_name = xstrdup (cpu_sub_arch_name);
+	  else
+	    top->sub_name = NULL;
+	  top->flags = cpu_arch_flags;
+	  top->isa = cpu_arch_isa;
+	  top->isa_flags = cpu_arch_isa_flags;
+	  top->flag_code = flag_code;
+	  top->stackop_size = stackop_size;
+	  top->no_cond_jump_promotion = no_cond_jump_promotion;
+
+	  top->prev = arch_stack_top;
+	  arch_stack_top = top;
+
+	  (void) restore_line_pointer (e);
+	  demand_empty_rest_of_line ();
+	  return;
+	}
+      else if (strcmp (string, "pop") == 0)
+	{
+	  const arch_stack_entry *top = arch_stack_top;
+
+	  if (!top)
+	    as_bad (_(".arch stack is empty"));
+	  else if (top->flag_code != flag_code
+		   || top->stackop_size != stackop_size)
+	    {
+	      static const unsigned int bits[] = {
+	        [CODE_16BIT] = 16,
+	        [CODE_32BIT] = 32,
+	        [CODE_64BIT] = 64,
+	      };
+
+	      as_bad (_("this `.arch pop' requires `.code%u%s' to be in effect"),
+		      bits[top->flag_code],
+		      top->stackop_size == LONG_MNEM_SUFFIX ? "gcc" : "");
+	    }
+	  else
+	    {
+	      arch_stack_top = top->prev;
+
+	      cpu_arch_name = top->name;
+	      free (cpu_sub_arch_name);
+	      cpu_sub_arch_name = top->sub_name;
+	      cpu_arch_flags = top->flags;
+	      cpu_arch_isa = top->isa;
+	      cpu_arch_isa_flags = top->isa_flags;
+	      no_cond_jump_promotion = top->no_cond_jump_promotion;
+
+	      XDELETE (top);
+	    }
+
+	  (void) restore_line_pointer (e);
+	  demand_empty_rest_of_line ();
+	  return;
+	}
 
       for (; j < ARRAY_SIZE (cpu_arch); j++)
 	{
@@ -13660,6 +13735,10 @@ show_arch (FILE *stream, int ext, int check)
     {
       p = output_message (stream, p, message, start, &left,
 			  STRING_COMMA_LEN ("default"));
+      p = output_message (stream, p, message, start, &left,
+			  STRING_COMMA_LEN ("push"));
+      p = output_message (stream, p, message, start, &left,
+			  STRING_COMMA_LEN ("pop"));
     }
 
   for (j = 0; j < ARRAY_SIZE (cpu_arch); j++)

gas/doc/c-i386.texi

@@ -1504,7 +1504,7 @@ directive enables a warning when gas detects an instruction that is not
 supported on the CPU specified.  The choices for @var{cpu_type} are:
 
 @multitable @columnfractions .20 .20 .20 .20
-@item @samp{default}
+@item @samp{default} @tab @samp{push} @tab @samp{pop}
 @item @samp{i8086} @tab @samp{i186} @tab @samp{i286} @tab @samp{i386}
 @item @samp{i486} @tab @samp{i586} @tab @samp{i686} @tab @samp{pentium}
 @item @samp{pentiumpro} @tab @samp{pentiumii} @tab @samp{pentiumiii} @tab @samp{pentium4}

gas/testsuite/gas/i386/arch-stk.l

@@ -0,0 +1,43 @@
+.*: Assembler messages:
+.*:3: Error:.*`cmovl'.*
+.*:10: Error:.*`cmovg'.*
+.*:17: Error:.*`cmovz'.*
+.*:21: Error:.*`\.arch pop'.*`\.code32'.*
+.*:28: Error:.*`\.arch pop'.*`\.code16gcc'.*
+.*:32: Error:.*\.arch.*empty.*
+GAS LISTING .*
+
+
+[ 	]*[0-9]*[ 	]+\.text
+[ 	]*[0-9]*[ 	]+start:
+[ 	]*[0-9]*[ 	]+cmovl	%eax, %ecx
+[ 	]*[0-9]*[ 	]*
+[ 	]*[0-9]*[ 	]+\.arch push
+[ 	]*[0-9]*[ 	]+\.arch default
+[ 	]*[0-9]*[ 	]+\?\?\?\? 0F4DC8[ 	]+cmovnl	%eax, %ecx
+[ 	]*[0-9]*[ 	]*
+[ 	]*[0-9]*[ 	]+\.arch pop
+[ 	]*[0-9]*[ 	]+cmovg	%eax, %ecx
+[ 	]*[0-9]*[ 	]*
+[ 	]*[0-9]*[ 	]+\.arch push
+[ 	]*[0-9]*[ 	]+\.arch \.cmov
+[ 	]*[0-9]*[ 	]+\?\?\?\? 0F4EC8[ 	]+cmovng	%eax, %ecx
+[ 	]*[0-9]*[ 	]*
+[ 	]*[0-9]*[ 	]+\.arch pop
+[ 	]*[0-9]*[ 	]+cmovz	%eax, %ecx
+[ 	]*[0-9]*[ 	]*
+[ 	]*[0-9]*[ 	]+\.arch push
+[ 	]*[0-9]*[ 	]+\.code16
+[ 	]*[0-9]*[ 	]+\.arch pop
+[ 	]*[0-9]*[ 	]+\.code32
+[ 	]*[0-9]*[ 	]+\.arch pop
+[ 	]*[0-9]*[ 	]*
+[ 	]*[0-9]*[ 	]+\.code16gcc
+[ 	]*[0-9]*[ 	]+\.arch push
+[ 	]*[0-9]*[ 	]+\.code32
+[ 	]*[0-9]*[ 	]+\.arch pop
+[ 	]*[0-9]*[ 	]+\.code16gcc
+[ 	]*[0-9]*[ 	]+\.arch pop
+[ 	]*[0-9]*[ 	]*
+[ 	]*[0-9]*[ 	]+\.arch pop
+#pass

gas/testsuite/gas/i386/arch-stk.s

@@ -0,0 +1,34 @@
+	.text
+start:
+	cmovl	%eax, %ecx
+
+	.arch push
+	.arch default
+	cmovnl	%eax, %ecx
+
+	.arch pop
+	cmovg	%eax, %ecx
+
+	.arch push
+	.arch .cmov
+	cmovng	%eax, %ecx
+
+	.arch pop
+	cmovz	%eax, %ecx
+
+	.arch push
+	.code16
+	.arch pop
+	.code32
+	.arch pop
+
+	.code16gcc
+	.arch push
+	.code32
+	.arch pop
+	.code16gcc
+	.arch pop
+
+	.arch pop
+
+	.end

gas/testsuite/gas/i386/i386.exp

@@ -206,6 +206,7 @@ if [gas_32_check] then {
     run_dump_test "arch-13"
     run_dump_test "arch-14"
     run_list_test "arch-dflt" "-march=generic32 -al"
+    run_list_test "arch-stk" "-march=generic32 -al"
     run_dump_test "8087"
     run_dump_test "287"
     run_dump_test "387"