glsl: Make is_16bit_constant from i965 an ir_constant method.

The i965 MUL instruction doesn't natively support 32-bit by 32-bit
integer multiplication; additional instructions (MACH/MOV) are required.
However, we can avoid those if we know one of the operands can be
represented in 16 bits or less.  The vector backend's is_16bit_constant
static helper function checks for this.

We want to be able to use it in the scalar backend as well, which means
moving the function to a more generally-usable location.  Since it isn't
i965 specific, I decided to make it an ir_constant method, in case it
ends up being useful to other people as well.

v2: Rename from is_16bit_integer_constant to is_uint16_constant, as
    suggested by Ilia Mirkin.  Update comments to clarify that it does
    apply to both int and uint types, as long as the value is
    non-negative and fits in 16-bits.

Signed-off-by: Kenneth Graunke <[email protected]>
Reviewed-by: Ian Romanick <[email protected]>
Reviewed-by: Matt Turner <[email protected]>

1 files changed, 15 insertions, 0 deletions

diff --git a/src/glsl/ir.h b/src/glsl/ir.h
index ee276d2be2d..6c7c60a27d9 100644
--- a/src/glsl/ir.h
+++ b/src/glsl/ir.h
@@ -265,6 +265,13 @@ public:
     */
    virtual bool is_basis() const;
 
+   /**
+    * Determine if an r-value is an unsigned integer constant which can be
+    * stored in 16 bits.
+    *
+    * \sa ir_constant::is_uint16_constant.
+    */
+   virtual bool is_uint16_constant() const { return false; }
 
    /**
     * Return a generic value of error_type.
@@ -2165,6 +2172,14 @@ public:
    virtual bool is_basis() const;
 
    /**
+    * Return true for constants that could be stored as 16-bit unsigned values.
+    *
+    * Note that this will return true even for signed integer ir_constants, as
+    * long as the value is non-negative and fits in 16-bits.
+    */
+   virtual bool is_uint16_constant() const;
+
+   /**
     * Value of the constant.
     *
     * The field used to back the values supplied by the constant is determined