s390: Print base register 0 as "0" in disassembly

Base and index register 0 have no effect in address computation:

"A value of zero in the B [base] or X [index] field specifies that no
base or index is to be applied, and, thus, general register 0 cannot be
designated as containing a base address or index."
IBM z/Architecture Principles of Operation [1], chapter "Organization",
section "General Registers".

Index register 0 is omitted in the s390 disassembly. Base register 0 is
omitted in D(B), D(L,B) and D(X,B) - the latter only if the index
register is zero.

To make it more apparent print base register 0 as "0" instead of "%r0",
whenever it would still be printed in the disassembly.

[1]: IBM z/Architecture Principles of Operation, SA22-7832-13,
     https://publibfp.dhe.ibm.com/epubs/pdf/a227832d.pdf

opcodes/
	* s390-dis.c: Print base register 0 as "0" in disassembly.

binutils/
	* NEWS: Mention base register 0 now being printed as "0" in s390
	disassembly.

gas/
	* testsuite/gas/s390/zarch-base-index-0.d: Update test case
	output verification patterns to accept "0" as base base
	register due to disassembler output format change.
	* gas/testsuite/gas/s390/zarch-omitted-base-index.d: Likewise.

Reviewed-by: Andreas Krebbel <krebbel@linux.ibm.com>
Signed-off-by: Jens Remus <jremus@linux.ibm.com>

4 files changed, 50 insertions, 39 deletions

diff --git a/binutils/NEWS b/binutils/NEWS
index 7b7ac1c..9c7c8f1 100644
--- a/binutils/NEWS
+++ b/binutils/NEWS
@@ -1,5 +1,7 @@
 -*- text -*-
 
+* Base register 0 is now printed as "0" instead of "%r0" in s390 disassembly.
+
 * When objdump or readelf are used to display the contents of a .eh_frame
   section they will now also display the contents of the .eh_frame_hdr section,
   if present.
diff --git a/gas/testsuite/gas/s390/zarch-base-index-0.d b/gas/testsuite/gas/s390/zarch-base-index-0.d
index e626604..4dd913b 100644
--- a/gas/testsuite/gas/s390/zarch-base-index-0.d
+++ b/gas/testsuite/gas/s390/zarch-base-index-0.d
@@ -17,8 +17,8 @@ Disassembly of section .text:
 .*:	5a 10 30 10 [	 ]*a	%r1,16\(%r3\)
 .*:	5a 10 30 10 [	 ]*a	%r1,16\(%r3\)
 .*:	5a 10 30 10 [	 ]*a	%r1,16\(%r3\)
-.*:	5a 12 00 10 [	 ]*a	%r1,16\(%r2,%r0\)
-.*:	5a 12 00 10 [	 ]*a	%r1,16\(%r2,%r0\)
+.*:	5a 12 00 10 [	 ]*a	%r1,16\(%r2,0\)
+.*:	5a 12 00 10 [	 ]*a	%r1,16\(%r2,0\)
 .*:	5a 10 00 10 [	 ]*a	%r1,16
 .*:	5a 10 00 10 [	 ]*a	%r1,16
 .*:	5a 10 00 10 [	 ]*a	%r1,16
@@ -31,46 +31,46 @@ Disassembly of section .text:
 .*:	5a 00 00 00 [	 ]*a	%r0,0
 .*:	5a 00 00 00 [	 ]*a	%r0,0
 .*:	d2 00 10 10 20 20 [	 ]*mvc	16\(1,%r1\),32\(%r2\)
-.*:	d2 00 00 10 20 20 [	 ]*mvc	16\(1,%r0\),32\(%r2\)
-.*:	d2 00 00 10 20 20 [	 ]*mvc	16\(1,%r0\),32\(%r2\)
-.*:	d2 00 00 10 20 20 [	 ]*mvc	16\(1,%r0\),32\(%r2\)
+.*:	d2 00 00 10 20 20 [	 ]*mvc	16\(1,0\),32\(%r2\)
+.*:	d2 00 00 10 20 20 [	 ]*mvc	16\(1,0\),32\(%r2\)
+.*:	d2 00 00 10 20 20 [	 ]*mvc	16\(1,0\),32\(%r2\)
 .*:	d2 00 10 10 00 20 [	 ]*mvc	16\(1,%r1\),32
 .*:	d2 00 10 10 00 20 [	 ]*mvc	16\(1,%r1\),32
 .*:	d2 00 10 10 00 20 [	 ]*mvc	16\(1,%r1\),32
-.*:	d2 00 00 10 00 20 [	 ]*mvc	16\(1,%r0\),32
-.*:	d2 00 00 10 00 20 [	 ]*mvc	16\(1,%r0\),32
-.*:	d2 00 00 10 00 20 [	 ]*mvc	16\(1,%r0\),32
-.*:	d2 00 00 10 00 20 [	 ]*mvc	16\(1,%r0\),32
-.*:	d2 00 00 10 00 20 [	 ]*mvc	16\(1,%r0\),32
-.*:	d2 00 00 10 00 20 [	 ]*mvc	16\(1,%r0\),32
-.*:	d2 00 00 10 00 20 [	 ]*mvc	16\(1,%r0\),32
-.*:	d2 00 00 10 00 20 [	 ]*mvc	16\(1,%r0\),32
-.*:	d2 00 00 10 00 20 [	 ]*mvc	16\(1,%r0\),32
-.*:	d2 00 00 00 00 00 [	 ]*mvc	0\(1,%r0\),0
+.*:	d2 00 00 10 00 20 [	 ]*mvc	16\(1,0\),32
+.*:	d2 00 00 10 00 20 [	 ]*mvc	16\(1,0\),32
+.*:	d2 00 00 10 00 20 [	 ]*mvc	16\(1,0\),32
+.*:	d2 00 00 10 00 20 [	 ]*mvc	16\(1,0\),32
+.*:	d2 00 00 10 00 20 [	 ]*mvc	16\(1,0\),32
+.*:	d2 00 00 10 00 20 [	 ]*mvc	16\(1,0\),32
+.*:	d2 00 00 10 00 20 [	 ]*mvc	16\(1,0\),32
+.*:	d2 00 00 10 00 20 [	 ]*mvc	16\(1,0\),32
+.*:	d2 00 00 10 00 20 [	 ]*mvc	16\(1,0\),32
+.*:	d2 00 00 00 00 00 [	 ]*mvc	0\(1,0\),0
 .*:	f3 01 10 10 20 20 [	 ]*unpk	16\(1,%r1\),32\(2,%r2\)
-.*:	f3 01 00 10 20 20 [	 ]*unpk	16\(1,%r0\),32\(2,%r2\)
-.*:	f3 01 00 10 20 20 [	 ]*unpk	16\(1,%r0\),32\(2,%r2\)
-.*:	f3 01 00 10 20 20 [	 ]*unpk	16\(1,%r0\),32\(2,%r2\)
-.*:	f3 01 10 10 00 20 [	 ]*unpk	16\(1,%r1\),32\(2,%r0\)
-.*:	f3 01 10 10 00 20 [	 ]*unpk	16\(1,%r1\),32\(2,%r0\)
-.*:	f3 01 10 10 00 20 [	 ]*unpk	16\(1,%r1\),32\(2,%r0\)
-.*:	f3 01 00 10 00 20 [	 ]*unpk	16\(1,%r0\),32\(2,%r0\)
-.*:	f3 01 00 10 00 20 [	 ]*unpk	16\(1,%r0\),32\(2,%r0\)
-.*:	f3 01 00 10 00 20 [	 ]*unpk	16\(1,%r0\),32\(2,%r0\)
-.*:	f3 01 00 10 00 20 [	 ]*unpk	16\(1,%r0\),32\(2,%r0\)
-.*:	f3 01 00 10 00 20 [	 ]*unpk	16\(1,%r0\),32\(2,%r0\)
-.*:	f3 01 00 10 00 20 [	 ]*unpk	16\(1,%r0\),32\(2,%r0\)
-.*:	f3 01 00 10 00 20 [	 ]*unpk	16\(1,%r0\),32\(2,%r0\)
-.*:	f3 01 00 10 00 20 [	 ]*unpk	16\(1,%r0\),32\(2,%r0\)
-.*:	f3 01 00 10 00 20 [	 ]*unpk	16\(1,%r0\),32\(2,%r0\)
-.*:	f3 01 00 00 00 00 [	 ]*unpk	0\(1,%r0\),0\(2,%r0\)
+.*:	f3 01 00 10 20 20 [	 ]*unpk	16\(1,0\),32\(2,%r2\)
+.*:	f3 01 00 10 20 20 [	 ]*unpk	16\(1,0\),32\(2,%r2\)
+.*:	f3 01 00 10 20 20 [	 ]*unpk	16\(1,0\),32\(2,%r2\)
+.*:	f3 01 10 10 00 20 [	 ]*unpk	16\(1,%r1\),32\(2,0\)
+.*:	f3 01 10 10 00 20 [	 ]*unpk	16\(1,%r1\),32\(2,0\)
+.*:	f3 01 10 10 00 20 [	 ]*unpk	16\(1,%r1\),32\(2,0\)
+.*:	f3 01 00 10 00 20 [	 ]*unpk	16\(1,0\),32\(2,0\)
+.*:	f3 01 00 10 00 20 [	 ]*unpk	16\(1,0\),32\(2,0\)
+.*:	f3 01 00 10 00 20 [	 ]*unpk	16\(1,0\),32\(2,0\)
+.*:	f3 01 00 10 00 20 [	 ]*unpk	16\(1,0\),32\(2,0\)
+.*:	f3 01 00 10 00 20 [	 ]*unpk	16\(1,0\),32\(2,0\)
+.*:	f3 01 00 10 00 20 [	 ]*unpk	16\(1,0\),32\(2,0\)
+.*:	f3 01 00 10 00 20 [	 ]*unpk	16\(1,0\),32\(2,0\)
+.*:	f3 01 00 10 00 20 [	 ]*unpk	16\(1,0\),32\(2,0\)
+.*:	f3 01 00 10 00 20 [	 ]*unpk	16\(1,0\),32\(2,0\)
+.*:	f3 01 00 00 00 00 [	 ]*unpk	0\(1,0\),0\(2,0\)
 .*:	e7 12 30 10 00 13 [	 ]*vgef	%v1,16\(%v2,%r3\),0
 .*:	e7 10 30 10 00 13 [	 ]*vgef	%v1,16\(%r3\),0
 .*:	e7 10 30 10 00 13 [	 ]*vgef	%v1,16\(%r3\),0
 .*:	e7 10 30 10 00 13 [	 ]*vgef	%v1,16\(%r3\),0
 .*:	e7 10 30 10 00 13 [	 ]*vgef	%v1,16\(%r3\),0
-.*:	e7 12 00 10 00 13 [	 ]*vgef	%v1,16\(%v2,%r0\),0
-.*:	e7 12 00 10 00 13 [	 ]*vgef	%v1,16\(%v2,%r0\),0
+.*:	e7 12 00 10 00 13 [	 ]*vgef	%v1,16\(%v2,0\),0
+.*:	e7 12 00 10 00 13 [	 ]*vgef	%v1,16\(%v2,0\),0
 .*:	e7 10 00 10 00 13 [	 ]*vgef	%v1,16,0
 .*:	e7 10 00 10 00 13 [	 ]*vgef	%v1,16,0
 .*:	e7 10 00 10 00 13 [	 ]*vgef	%v1,16,0
diff --git a/gas/testsuite/gas/s390/zarch-omitted-base-index.d b/gas/testsuite/gas/s390/zarch-omitted-base-index.d
index b2ff292..cb168a2 100644
--- a/gas/testsuite/gas/s390/zarch-omitted-base-index.d
+++ b/gas/testsuite/gas/s390/zarch-omitted-base-index.d
@@ -18,5 +18,5 @@ Disassembly of section .text:
 .*:	e7 10 00 10 00 13 [	 ]*vgef	%v1,16,0
 .*:	d2 00 10 10 20 20 [	 ]*mvc	16\(1,%r1\),32\(%r2\)
 .*:	d2 00 10 10 00 20 [	 ]*mvc	16\(1,%r1\),32
-.*:	d2 00 00 10 20 20 [	 ]*mvc	16\(1,%r0\),32\(%r2\)
-.*:	d2 00 00 10 00 20 [	 ]*mvc	16\(1,%r0\),32
+.*:	d2 00 00 10 20 20 [	 ]*mvc	16\(1,0\),32\(%r2\)
+.*:	d2 00 00 10 00 20 [	 ]*mvc	16\(1,0\),32
diff --git a/opcodes/s390-dis.c b/opcodes/s390-dis.c
index a4cba77..ee2f2cb 100644
--- a/opcodes/s390-dis.c
+++ b/opcodes/s390-dis.c
@@ -234,8 +234,13 @@ s390_print_insn_with_opcode (bfd_vma memaddr,
 	{
 	  info->fprintf_styled_func (info->stream, dis_style_text,
 				     "%c", separator);
-	  info->fprintf_styled_func (info->stream, dis_style_register,
-				     "%%r%u", val.u);
+	  if ((flags & (S390_OPERAND_BASE | S390_OPERAND_INDEX))
+	      && val.u == 0)
+	    info->fprintf_styled_func (info->stream, dis_style_register,
+				       "%u", val.u);
+	  else
+	    info->fprintf_styled_func (info->stream, dis_style_register,
+				       "%%r%u", val.u);
 	}
       else if (flags & S390_OPERAND_FPR)
 	{
@@ -248,8 +253,12 @@ s390_print_insn_with_opcode (bfd_vma memaddr,
 	{
 	  info->fprintf_styled_func (info->stream, dis_style_text,
 				     "%c", separator);
-	  info->fprintf_styled_func (info->stream, dis_style_register,
-				     "%%v%i", val.u);
+	  if ((flags & S390_OPERAND_INDEX) && val.u == 0)
+	    info->fprintf_styled_func (info->stream, dis_style_register,
+				       "%u", val.u);
+	  else
+	    info->fprintf_styled_func (info->stream, dis_style_register,
+				       "%%v%i", val.u);
 	}
       else if (flags & S390_OPERAND_AR)
 	{