[binutils-gdb] x86: zap value-less Disp8MemShift from non-EVEX templates

[Jan Beulich]

https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;h=d125c4bbce8398819df573754c2bf1224a15ec06

commit d125c4bbce8398819df573754c2bf1224a15ec06
Author: Jan Beulich <jbeulich@suse.com>
Date:   Fri May 3 09:24:48 2024 +0200

    x86: zap value-less Disp8MemShift from non-EVEX templates
    
    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.

Diff:
---
 opcodes/i386-gen.c | 26 +++++++++++++++++++-------
 1 file changed, 19 insertions(+), 7 deletions(-)

diff --git a/opcodes/i386-gen.c b/opcodes/i386-gen.c
index 3f63d157df6..35e2f27df3b 100644
--- a/opcodes/i386-gen.c
+++ b/opcodes/i386-gen.c
@@ -1126,6 +1126,7 @@ process_i386_opcode_modifier (FILE *table, char *mod, unsigned int space,
 			      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 *table, char *mod, unsigned int space,
 	      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 *table, char *mod, unsigned int space,
 
   /* 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.  */