Added the LDRIRW variant of the LDR instruction

src/execution-engine-spec/instructions.adoc

@@ -147,8 +147,19 @@ Assembler syntax::
 +
 [source]
 ----
-ldr{cond} dst, [src, off]
+ldr<cond?> <dst>, [<src>, <off?>]
 ----
++
+Where:
+[horizontal]
+cond::: Optional condition.
+dst::: Destination register.
+src::: Source register.
+off:::
+    Optional offset immediate.
+    Must be a multiple of 4 and in the range 0-8188.
+    If omitted, then 0 is used.
+
 Examples::
 +
 [source]
@@ -160,6 +171,50 @@ ldr.eq r5, [r4]    ; If the last comparison resulted in an 'eq' condition status
                    ; then reads a word from the memory address in r4 into r5.
                    ; Else, does nothing.
 ----
+
+Privileged instruction:: No.
+Updates program state flags:: No.
+Exceptions::
+[horizontal]
+    MemFault:::
+        If the memory address being accessed is invalid, non readable or not paged in.
+        The kernel may update the page table entries and re-execute the instruction without the user application being aware that it failed in the first place.
+
+====== LDRIRW: Load Register Immediate Pre-indexed with Write-back
+Description::
+    Increments the source register then reads a word from memory into the destination register.
+    The immediate offset `off` is added to the `src` register value before reading a word from memory into the `dst` register.
+Encoding:: A-Type
+Assembler syntax::
++
+[source]
+----
+ldr<cond?> <dst>, ![<src>, <off?>]
+----
++
+Where:
+[horizontal]
+cond::: Optional condition.
+dst::: Destination register.
+src::: Source register.
+off:::
+    Optional offset immediate.
+    Must be a multiple of 4 and in the range 0-8188.
+    If omitted, then 4 is used.
+
+Examples::
++
+[source]
+----
+ldr    r1, ![r0]    ; Increments r0 by 4 then reads a word from the memory address
+                    ; in r0 into r1.
+ldr    r3, ![r2, 8] ; Increments r2 by 8 then reads a word from the memory address
+                    ; in r2 into r3.
+ldr.eq r5, ![r4]    ; If the last comparison resulted in an 'eq' condition status,
+                    ; then increments r4 by 4 and reads a word from the memory
+                    ; address in r4 into r5. Else, does nothing.
+----
+
 Privileged instruction:: No.
 Updates program state flags:: No.
 Exceptions::