Add CPU flags value types to the language reference manual.

Clean up a few other things in the value types section too.

cranelift/docs/langref.rst

@@ -99,22 +99,7 @@ to represent, more bits are often used when holding a boolean value in a
 register or in memory. The :type:`b1` type represents an abstract boolean
 value. It can only exist as an SSA value, it can't be stored in memory or
 converted to another type. The larger boolean types can be stored in memory.
-
+They are represented as either all zero bits or all one bits.
-.. todo:: Clarify the representation of larger boolean types.
-
-    The multi-bit boolean types can be interpreted in different ways. We could
-    declare that zero means false and non-zero means true. This may require
-    unwanted normalization code in some places.
-
-    We could specify a fixed encoding like all ones for true. This would then
-    lead to undefined behavior if untrusted code uses the multibit booleans
-    incorrectly.
-
-    Something like this:
-
-    - External code is not allowed to load/store multi-bit booleans or
-      otherwise expose the representation.
-    - Each target specifies the exact representation of a multi-bit boolean.
 
 .. autoctontype:: b1
 .. autoctontype:: b8
@@ -144,6 +129,20 @@ double-double formats.
 .. autoctontype:: f32
 .. autoctontype:: f64
 
+CPU flags types
+---------------
+
+Some target ISAs use CPU flags to represent the result of a comparison. These
+CPU flags are represented as two value types depending on the type of values
+compared.
+
+Since some ISAs don't have CPU flags, these value types should not be used
+until the legalization phase of compilation where the code is adapted to fit
+the target ISA. Use instructions like :inst:`icmp` instead.
+
+.. autoctontype:: iflags
+.. autoctontype:: fflags
+
 SIMD vector types
 -----------------
 
@@ -194,7 +193,7 @@ Pseudo-types and type classes
 These are not concrete types, but convenient names uses to refer to real types
 in this reference.
 
-.. type:: iPtr
+.. type:: iAddr
 
     A Pointer-sized integer.
 
@@ -225,10 +224,6 @@ in this reference.
 
     Any type that can be stored in memory: :type:`Int` or :type:`Float`.
 
-.. type:: Logic
-
-    Either :type:`b1` or :type:`b1xN`.
-
 .. type:: Testable
 
     Either :type:`b1` or :type:`iN`.

lib/cretonne/meta/base/types.py

@@ -35,12 +35,12 @@ f64 = FloatType(
 iflags = FlagsType(
         'iflags', """
         CPU flags representing the result of an integer comparison. These flags
-        can be tested with an `intcc` condition code.
+        can be tested with an :type:`intcc` condition code.
         """)
 
 #: CPU flags from a floating point comparison.
 fflags = FlagsType(
         'fflags', """
         CPU flags representing the result of a floating point comparison. These
-        flags can be tested with a `floatcc` condition code.
+        flags can be tested with a :type:`floatcc` condition code.
         """)