[PATCH v6 2/7] ppc: introduce non-zero operand flag

[Dmitry Selyutin <ghostmansd@gmail.com>]

svstep and svshape instructions subtract 1 before encoding some of the
operands. Obviously zero is not supported for these operands. Whilst
PPC_OPERAND_PLUS1 fits perfectly to mark that maximal value should be
incremented, there is no flag which marks the fact that zero values are
not allowed. This patch adds a new flag, PPC_OPERAND_NONZERO, for this
purpose.
---
 gas/config/tc-ppc.c  | 22 +++++++++++++++++++---
 include/opcode/ppc.h |  7 +++++++
 opcodes/ppc-dis.c    |  3 +++
 3 files changed, 29 insertions(+), 3 deletions(-)

diff --git a/gas/config/tc-ppc.c b/gas/config/tc-ppc.c
index ffc99857e3..7bd2fe785d 100644
--- a/gas/config/tc-ppc.c
+++ b/gas/config/tc-ppc.c
@@ -1656,10 +1656,16 @@ ppc_setup_opcodes (void)
 	 all the 1's in the mask are contiguous.  */
       for (i = 0; i < num_powerpc_operands; ++i)
 	{
+
 	  uint64_t mask = powerpc_operands[i].bitm;
+          unsigned long flags = powerpc_operands[i].flags;
 	  uint64_t right_bit;
 	  unsigned int j;
 
+	  if ((flags & (PPC_OPERAND_PLUS1 | PPC_OPERAND_NONZERO)) ==
+	        (PPC_OPERAND_PLUS1 | PPC_OPERAND_NONZERO))
+	    as_bad ("mutually exclusive operand flags");
+
 	  right_bit = mask & -mask;
 	  mask += right_bit;
 	  right_bit = mask & -mask;
@@ -1992,6 +1998,11 @@ ppc_insert_operand (uint64_t insn,
       max = (max >> 1) & -right;
       min = ~max & -right;
     }
+  else if ((operand->flags & PPC_OPERAND_NONZERO) != 0)
+    {
+      ++min;
+      ++max;
+    }
 
   if ((operand->flags & PPC_OPERAND_PLUS1) != 0)
     max++;
@@ -2042,10 +2053,15 @@ ppc_insert_operand (uint64_t insn,
       if (errmsg != (const char *) NULL)
 	as_bad_where (file, line, "%s", errmsg);
     }
-  else if (operand->shift >= 0)
-    insn |= (val & operand->bitm) << operand->shift;
   else
-    insn |= (val & operand->bitm) >> -operand->shift;
+    {
+      if ((operand->flags & PPC_OPERAND_NONZERO) != 0)
+	--val;
+      if (operand->shift >= 0)
+	insn |= (val & operand->bitm) << operand->shift;
+      else
+	insn |= (val & operand->bitm) >> -operand->shift;
+    }
 
   return insn;
 }
diff --git a/include/opcode/ppc.h b/include/opcode/ppc.h
index d5752a42e6..df06671db4 100644
--- a/include/opcode/ppc.h
+++ b/include/opcode/ppc.h
@@ -463,6 +463,13 @@ extern const unsigned int num_powerpc_operands;
 #define PPC_OPERAND_FCR (0x1000000)
 #define PPC_OPERAND_UDI (0x2000000)
 
+/*
+ * Valid range of operand is 1..n rather than 0..n-1.
+ * Before encoding, the operand value is decremented.
+ * After decoding. the operand value is incremented.
+ */
+#define PPC_OPERAND_NONZERO 0x4000000
+
 extern ppc_cpu_t ppc_parse_cpu (ppc_cpu_t, ppc_cpu_t *, const char *);
 
 static inline int64_t
diff --git a/opcodes/ppc-dis.c b/opcodes/ppc-dis.c
index f61e6518f1..d5b23c8a75 100644
--- a/opcodes/ppc-dis.c
+++ b/opcodes/ppc-dis.c
@@ -545,6 +545,9 @@ operand_value_powerpc (const struct powerpc_operand *operand,
 	}
     }
 
+  if ((operand->flags & PPC_OPERAND_NONZERO) != 0)
+    ++value;
+
   return value;
 }
 
-- 
2.37.0