[PATCH, GAS/ARM] Clarify relation between reg_expected_msgs and arm_reg_type

[Thomas Preudhomme <thomas dot preudhomme at foss dot arm dot com>]

Hi,

Uses of reg_expected_msgs rely on each arm_reg_type enumerator to have a
message entry in the same order as the enumerator declaration. This is
not clearly stated in the definition of both the arm_reg_type enum and
the reg_expected_msgs. Worse, there is nothing to ensure both are kept
in sync.

As an attempt towards this, this patch uses C99 array designators to
ensure that each message is associated with the right arm_reg_type. A
comment is also added near the definition of arm_reg_type to point to
the reg_expected_msgs array. Finally, the array is synced with
arm_reg_type by adding the missing error message for REG_TYPE_RNB.

ChangeLog entry is as follows:

*** gas/ChangeLog ***

2017-11-14  Thomas Preud'homme  <thomas.preudhomme@arm.com>

	* config/tc-arm.c (arm_reg_type): Comment on the link with
	reg_expected_msgs.
	(reg_expected_msgs): Initialize using array designators with
	arm_reg_type index.

Testing: Ran testsuite for arm-none-eabi target; it showed no
regression.

Is this ok for master?

Best regards,

Thomas

diff --git a/gas/config/tc-arm.c b/gas/config/tc-arm.c
index 5e9939ac03e4e82ca919d49e703765013462e3a3..70e9df1acec36a708317dbda5c46ed100418e1f6 100644
--- a/gas/config/tc-arm.c
+++ b/gas/config/tc-arm.c
@@ -571,7 +571,8 @@ struct neon_typed_alias
 };
 
 /* ARM register categories.  This includes coprocessor numbers and various
-   architecture extensions' registers.	*/
+   architecture extensions' registers.  Each entry should have an error message
+   in reg_expected_msgs below.  */
 enum arm_reg_type
 {
   REG_TYPE_RN,
@@ -615,28 +616,30 @@ struct reg_entry
 /* Diagnostics used when we don't get a register of the expected type.	*/
 const char * const reg_expected_msgs[] =
 {
-  N_("ARM register expected"),
-  N_("bad or missing co-processor number"),
-  N_("co-processor register expected"),
-  N_("FPA register expected"),
-  N_("VFP single precision register expected"),
-  N_("VFP/Neon double precision register expected"),
-  N_("Neon quad precision register expected"),
-  N_("VFP single or double precision register expected"),
-  N_("Neon double or quad precision register expected"),
-  N_("Neon single or double precision register expected"),
-  N_("VFP single, double or Neon quad precision register expected"),
-  N_("VFP system register expected"),
-  N_("Maverick MVF register expected"),
-  N_("Maverick MVD register expected"),
-  N_("Maverick MVFX register expected"),
-  N_("Maverick MVDX register expected"),
-  N_("Maverick MVAX register expected"),
-  N_("Maverick DSPSC register expected"),
-  N_("iWMMXt data register expected"),
-  N_("iWMMXt control register expected"),
-  N_("iWMMXt scalar register expected"),
-  N_("XScale accumulator register expected"),
+  [REG_TYPE_RN]	    = N_("ARM register expected"),
+  [REG_TYPE_CP]	    = N_("bad or missing co-processor number"),
+  [REG_TYPE_CN]	    = N_("co-processor register expected"),
+  [REG_TYPE_FN]	    = N_("FPA register expected"),
+  [REG_TYPE_VFS]    = N_("VFP single precision register expected"),
+  [REG_TYPE_VFD]    = N_("VFP/Neon double precision register expected"),
+  [REG_TYPE_NQ]	    = N_("Neon quad precision register expected"),
+  [REG_TYPE_VFSD]   = N_("VFP single or double precision register expected"),
+  [REG_TYPE_NDQ]    = N_("Neon double or quad precision register expected"),
+  [REG_TYPE_NSD]    = N_("Neon single or double precision register expected"),
+  [REG_TYPE_NSDQ]   = N_("VFP single, double or Neon quad precision register"
+			 " expected"),
+  [REG_TYPE_VFC]    = N_("VFP system register expected"),
+  [REG_TYPE_MVF]    = N_("Maverick MVF register expected"),
+  [REG_TYPE_MVD]    = N_("Maverick MVD register expected"),
+  [REG_TYPE_MVFX]   = N_("Maverick MVFX register expected"),
+  [REG_TYPE_MVDX]   = N_("Maverick MVDX register expected"),
+  [REG_TYPE_MVAX]   = N_("Maverick MVAX register expected"),
+  [REG_TYPE_DSPSC]  = N_("Maverick DSPSC register expected"),
+  [REG_TYPE_MMXWR]  = N_("iWMMXt data register expected"),
+  [REG_TYPE_MMXWC]  = N_("iWMMXt control register expected"),
+  [REG_TYPE_MMXWCG] = N_("iWMMXt scalar register expected"),
+  [REG_TYPE_XSCALE] = N_("XScale accumulator register expected"),
+  [REG_TYPE_RNB]    = N_("")
 };
 
 /* Some well known registers that we refer to directly elsewhere.  */