Kenneth Graunke <kenn...@whitecape.org> writes: > Consider the following code sequence: > > mul(8) g4<1>F g1<0,4,1>.wzwwF g3<4,4,1>.wzwwF > mov.sat(8) m1<1>.xyF g4<4,4,1>F > mul(8) g4<1>F g1<0,4,1>.xxyxF g3<4,4,1>.xxyxF > mov.sat(8) m1<1>.zwF g4<4,4,1>F > > The compute-to-MRF pass will discover the first mov.sat and attempt to > replace it by rewriting earlier instructions. Everything works out, > so it replaces scan_inst's destination file, reg, and reg_offset, > resulting in: > > mul(8) m1<1>F g1<0,4,1>.wzwwF g3<4,4,1>.wzwwF > mul(8) g4<1>F g1<0,4,1>.xxyxF g3<4,4,1>.xxyxF > mov.sat(8) m1<1>.zwF g4<4,4,1>F > > Unfortunately, it loses the .xy writemask on the mov.sat's MRF > destination. While this doesn't pose an immediate problem, it then > proceeds to transform the second mov.sat, resulting in: > > mul(8) m1<1>F g1<0,4,1>.wzwwF g3<4,4,1>.wzwwF > mul(8) m1<1>F g1<0,4,1>.xxyxF g3<4,4,1>.xxyxF > > Instead of writing both halves of the vector (like the original code), > it overwrites the full vector both times, clobbering the desired .xy > values. > > When encountering a MOV, the compute-to-MRF code scans for instructions > which generate channels of the MOV source. It ensures that all > necessary channels are available (possibly written by several > instructions). In this case, *more* channels are available than > necessary, so we want to take the subset that's actually used. > Taking the bitwise and of both writemasks should accomplish that. > > This was discovered by analyzing an ARB_vertex_program test > (glean/vertProg1/MUL test (with swizzle and masking)) with my new > Mesa IR -> Vec4 IR translator code. However, it should be possible > with GLSL programs as well. > > NOTE: This is a candidate for stable release branches. > > Cc: Eric Anholt <e...@anholt.net> > Signed-off-by: Kenneth Graunke <kenn...@whitecape.org>
Thanks for the asm in the commit message, which made things clear. Reviewed-by: Eric Anholt <e...@anholt.net>
pgpERawFFjoFG.pgp
Description: PGP signature
_______________________________________________ mesa-dev mailing list mesa-dev@lists.freedesktop.org http://lists.freedesktop.org/mailman/listinfo/mesa-dev
