[PATCH v2 3/4] x86: adjust segment override prefix emission

[Jan Beulich <jbeulich@suse.com>]

Since we already suppress the prefix altogether when it's the default
one for the chosen addressing mode, let's do so also when instruction
prefix and override specified with the memory operand match. (Note that
insn prefix specified segment overrides never get discarded.)

gas/
2020-02-XX  Jan Beulich  <jbeulich@suse.com>

	* config/tc-i386.c (process_operands): Also skip segment
	override prefix emission if it matches an already present one.
	* testsuite/gas/i386/prefix32.s: Add double segment override
	cases.
	* testsuite/gas/i386/prefix32.l: Adjust expectations.

--- a/gas/config/tc-i386.c
+++ b/gas/config/tc-i386.c
@@ -7208,11 +7208,12 @@ duplicate:
     }
 
   /* If a segment was explicitly specified, and the specified segment
-     is not the default, use an opcode prefix to select it.  If we
-     never figured out what the default segment is, then default_seg
-     will be zero at this point, and the specified segment prefix will
-     always be used.  */
-  if ((i.seg[0]) && (i.seg[0] != default_seg))
+     is neither the default nor the one already recorded from a prefix,
+     use an opcode prefix to select it.  If we never figured out what
+     the default segment is, then default_seg will be zero at this
+     point, and the specified segment prefix will always be used.  */
+  if ((i.seg[0]) && (i.seg[0] != default_seg)
+      && (i.seg[0]->seg_prefix != i.prefix[SEG_PREFIX]))
     {
       if (!add_prefix (i.seg[0]->seg_prefix))
 	return 0;
--- a/gas/testsuite/gas/i386/prefix32.l
+++ b/gas/testsuite/gas/i386/prefix32.l
@@ -8,6 +8,7 @@
 .*:19: Error: same type of prefix .*
 .*:20: Error: data size .* `vaddps'
 .*:21: Error: data size .* `vaddpd'
+.*:25: Error: same type of prefix .*
 GAS LISTING .*
 #...
 [ 	]*1[ 	]+\.text
@@ -33,4 +34,10 @@ GAS LISTING .*
 [ 	]*20[ 	]+data16 vaddps	%xmm0, %xmm0, %xmm0
 [ 	]*21[ 	]+data16 vaddpd	%xmm0, %xmm0, %xmm0
 [ 	]*22[ 	]*
-[ 	]*23[ 	]*[\?]+ 0+[ \t]+\.p2align	4,0
+[ 	]*23[ 	]+\.Lsegment:
+[ 	]*24[ 	]+\?\?\?\? 368B4500[ 	]+ss mov		%ss:\(%ebp\), %eax
+[ 	]*25[ 	]+ss mov		%ds:\(%ebp\), %eax
+[ 	]*26[ 	]+\?\?\?\? 3E8B4500[ 	]+ds mov		%ss:\(%ebp\), %eax
+[ 	]*27[ 	]+\?\?\?\? 3E8B4500[ 	]+ds mov		%ds:\(%ebp\), %eax
+[ 	]*28[ 	]*
+#pass
--- a/gas/testsuite/gas/i386/prefix32.s
+++ b/gas/testsuite/gas/i386/prefix32.s
@@ -20,4 +20,10 @@ prefix:
 	data16 vaddps	%xmm0, %xmm0, %xmm0
 	data16 vaddpd	%xmm0, %xmm0, %xmm0
 
+.Lsegment:
+	ss mov		%ss:(%ebp), %eax
+	ss mov		%ds:(%ebp), %eax
+	ds mov		%ss:(%ebp), %eax
+	ds mov		%ds:(%ebp), %eax
+
 	.p2align	4,0