[PATCH v2 1/4] x86: zap value-less Disp8MemShift from non-EVEX templates

[Jan Beulich <jbeulich@suse.com>]

In order to allow to continue to use templatized SSE2AVX templates when
enhancing those to also cover eGPR usage, Disp8MemShift wants using to
deviate from what general template attributes supply. That requires
using Disp8MemShift in a way also affecting non-EVEX templates, yet
having this attribute set would so far implicitly mean EVEX encoding.
Recognize the case and instead zap the attribute if no other attribute
indicates EVEX encoding.

No change in generated tables.
---
This could be folded into the subsequent "x86/APX: extend SSE2AVX
coverage", but I think it's better kept separate for being a little
subtle.

--- a/opcodes/i386-gen.c
+++ b/opcodes/i386-gen.c
@@ -1126,6 +1126,7 @@ process_i386_opcode_modifier (FILE *tabl
 			      char **opnd, int lineno, bool rex2_disallowed)
 {
   char *str, *next, *last;
+  bool disp8_shift_derived = false;
   bitfield modifiers [ARRAY_SIZE (opcode_modifiers)];
   static const char *const spaces[] = {
 #define SPACE(n) [SPACE_##n] = #n
@@ -1190,7 +1191,10 @@ process_i386_opcode_modifier (FILE *tabl
 	      if (strcasecmp(str, "Broadcast") == 0)
 		val = get_element_size (opnd, lineno) + BYTE_BROADCAST;
 	      else if (strcasecmp(str, "Disp8MemShift") == 0)
-		val = get_element_size (opnd, lineno);
+		{
+		  val = get_element_size (opnd, lineno);
+		  disp8_shift_derived = true;
+		}
 
 	      set_bitfield (str, modifiers, val, ARRAY_SIZE (modifiers),
 			    lineno);
@@ -1243,13 +1247,21 @@ process_i386_opcode_modifier (FILE *tabl
 
   /* Rather than evaluating multiple conditions at runtime to determine
      whether an EVEX encoding is being dealt with, derive that information
-     right here.  A missing EVex attribute means "dynamic".  */
-  if (!modifiers[EVex].value
-      && (modifiers[Disp8MemShift].value
-	  || modifiers[Broadcast].value
+     right here.  A missing EVex attribute means "dynamic".  There's one
+     exception though: A value-less Disp8MemShift needs zapping rather than
+     respecting if no other attribute indicates EVEX encoding.  This is for
+     certain SSE2AVX templatized templates to work reasonably.  */
+  if (!modifiers[EVex].value)
+    {
+      if (modifiers[Broadcast].value
 	  || modifiers[Masking].value
-	  || modifiers[SAE].value))
-    modifiers[EVex].value = EVEXDYN;
+	  || modifiers[SAE].value)
+	modifiers[EVex].value = EVEXDYN;
+      else if (disp8_shift_derived)
+	modifiers[Disp8MemShift].value = 0;
+      else if (modifiers[Disp8MemShift].value)
+	modifiers[EVex].value = EVEXDYN;
+    }
 
   /* Vex, legacy map2 and map3 and rex2_disallowed do not support EGPR.
      For templates supporting both Vex and EVex allowing EGPR.  */