On Thu, Apr 7, 2011 at 3:06 AM, Tom Stellard <tstel...@gmail.com> wrote:
I don't know anything about this code, but I just want to verify that T0 (tee zero) and TO (tee oh) are different things and are used in the right places. > +/** > + * This pass replaces CMP T0, T1 T2 T0 with MOV TO, T2 when the CMP > + * instruction is the first instruction to write to register T0. The are > + * several lowering passes done in GLSL IR (e.g. branches and > + * relative addressing) that create a large number of conditional assignments > + * that ir_to_mesa converts to CMP instructions like the one mentioned above. > + * > + * Here is why this conversion is safe: > + * CMP TO, T1 T2 T0 can be expanded to: > + * if (T1 < 0.0) > + * MOV T0, T2; > + * else > + * MOV T0, TO; > + * > + * If (T1 < 0.0) evaluates to true then our replacement MOV T0, T2 is the > same > + * as the original program. If (T1 < 0.0) evaluates to false, executing > + * MOV T0, T0 will store a garbage value in T0 since T0 is uninitialized. > + * Therefore, it doesn't matter that we are replacing MOV T0, T0 with MOV > TO, T2 > + * because any instruction that was going to read from T0 after this was > going > + * to read a garbage value anyway. I see "This pass replaces CMP T0, T1 T2 T0" but also "CMP TO, T1 T2 T0 can be expanded to" where the first has T0 twice and the second has TO and T0. And a few other seemingly strange occurrences of TO also. Matt _______________________________________________ mesa-dev mailing list mesa-dev@lists.freedesktop.org http://lists.freedesktop.org/mailman/listinfo/mesa-dev
