[PATCH 0/4] s390: Make vector index register operands mandatory

[Jens Remus]

Index register operands in a conventional displacement D, index X, and
base (B) triplet "D(X,B)" are treated as optional.  This is because
register 0 contents are not used in conventional addressing
computations.  Instead a value of zero is implied.
The assembler therefore implies register 0, if an index/base register
is omitted (e.g. when coding "D(,B)" or "D(B)").
The disassembler disassembles index/base register 0 as "0" instead of
"%r0", as this clarifies that a value of zero is implied instead of
using the contents of register 0.

Vector index register operands, so far only used in the VRV instruction
format, are different though.  Vector index register 0 contents are used
in the addressing computation:

"For VRV format instructions, a vector element is used in the formation
of the intermediate value.  This vector element is an unsigned binary
integer value that is added to the base address and 12-bit displacement
to form a 64-bit intermediate sum.  The vector element is designated by
a vector register and an element index.  A zero V field accesses the
element in vector register zero and does not imply a zero value." [1]

Therefore make the following changes to the assembler and disassembler:

Patch 2 changes the disassembler to no longer omit vector index
register 0 operands in disassembly.  Furthermore it disassembles them
as "%v0" instead of "0" to clarify, that the vector register 0 value is
used in the addressing computation.

Patch 3 changes the assembler not to warn about vector index register 0
being used.

Patch 4 changes the assembler to require the specification of vector
index register operands.  That is they may no longer be omitted.  This
is a non-backward compatible change.  The rationale is that any (very
unlikely) existing assembler code that omits the specification of
vector index register 0, may potentially be in error, as the programmer
may likely have assumed a value of zero to be implied instead of vector
register 0 contents to be used.

Regards,
Jens

Jens Remus (4):
  s390: Additional tests for omitted base register operands
  s390: Do not omit vector index register 0 in disassembly
  s390: Do not warn about vector index register 0 in assembly
  s390: Error if vector index register omitted in assembly

 gas/config/tc-s390.c                          | 13 ++++-
 .../gas/s390/zarch-base-index-0-err.l         | 18 ++++--
 .../gas/s390/zarch-base-index-0-err.s         | 10 +++-
 gas/testsuite/gas/s390/zarch-base-index-0.d   | 26 +++------
 gas/testsuite/gas/s390/zarch-base-index-0.s   | 18 +++---
 .../gas/s390/zarch-omitted-base-index-err.l   | 37 ++++++------
 .../gas/s390/zarch-omitted-base-index-err.s   |  3 +
 .../gas/s390/zarch-omitted-base-index.d       |  5 +-
 .../gas/s390/zarch-omitted-base-index.s       |  6 +-
 gas/testsuite/gas/s390/zarch-warn-areg-zero.l | 16 +++---
 gas/testsuite/gas/s390/zarch-warn-areg-zero.s | 56 +++++++++----------
 opcodes/s390-dis.c                            | 13 ++---
 12 files changed, 121 insertions(+), 100 deletions(-)

-- 
2.45.2