Currently the execution type calculation will return a bogus value in
cases like:
mov_indirect(8) vgrf0:w, vgrf1:w, vgrf2:ud, 32u
Which will be considered to have a 32-bit integer execution type even
though the actual indirect move operation will be carried out with
16-bit precision.
Similarly there's no need to apply the CHV/BXT double-precision region
alignment restrictions to such control sources, since they aren't
directly involved in the double-precision arithmetic operations
emitted by these virtual instructions. Applying the CHV/BXT
restrictions to control sources was expected to be harmless if mildly
inefficient, but unfortunately it exposed problems at codegen level
for virtual instructions (namely the SHUFFLE instruction used for the
Vulkan 1.1 subgroup feature) that weren't prepared to accept control
sources with an arbitrary strided region.
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=109328
Reported-by: Mark Janes <mark.a.janes@intel.com>
Fixes: efa4e4bc5f "intel/fs: Introduce regioning lowering pass."
Tested-by: Anuj Phogat <anuj.phogat@gmail.com>
Reviewed-by: Jason Ekstrand <jason@jlekstrand.net>
In some shaders, you can end up with a stride in the source of a
SHADER_OPCODE_MULH. One way this can happen is if the MULH is acting on
the top bits of a 64-bit value due to 64-bit integer lowering. In this
case, the compiler will produce something like this:
mul(8) acc0<1>UD g5<8,4,2>UD 0x0004UW { align1 1Q };
mach(8) g6<1>UD g5<8,4,2>UD 0x00000004UD { align1 1Q AccWrEnable };
The new region fixup pass looks at the MUL and sees a strided source and
unstrided destination and determines that the sequence is illegal. It
then attempts to fix the illegal stride by replacing the destination of
the MUL with a temporary and emitting a MOV into the accumulator:
mul(8) g9<2>UD g5<8,4,2>UD 0x0004UW { align1 1Q };
mov(8) acc0<1>UD g9<8,4,2>UD { align1 1Q };
mach(8) g6<1>UD g5<8,4,2>UD 0x00000004UD { align1 1Q AccWrEnable };
Unfortunately, this new sequence isn't correct because MOV accesses the
accumulator with a different precision to MUL and, instead of filling
the bottom 32 bits with the source and zeroing the top 32 bits, it
leaves the top 32 (or maybe 31) bits alone and full of garbage. When
the MACH comes along and tries to complete the multiplication, the
result is correct in the bottom 32 bits (which we throw away) and
garbage in the top 32 bits which are actually returned by MACH.
This commit does two things: First, it adds an assert to ensure that we
don't try to rewrite accumulator destinations of MUL instructions so we
can avoid this precision issue. Second, it modifies
required_dst_byte_stride to require a tightly packed stride so that we
fix up the sources instead and the actual code which gets emitted is
this:
mov(8) g9<1>UD g5<8,4,2>UD { align1 1Q };
mul(8) acc0<1>UD g9<8,8,1>UD 0x0004UW { align1 1Q };
mach(8) g6<1>UD g5<8,4,2>UD 0x00000004UD { align1 1Q AccWrEnable };
Fixes: efa4e4bc5f "intel/fs: Introduce regioning lowering pass"
Reviewed-by: Francisco Jerez <currojerez@riseup.net>
This legalization pass is meant to handle situations where the source
or destination regioning controls of an instruction are unsupported by
the hardware and need to be lowered away into separate instructions.
This should be more reliable and future-proof than the current
approach of handling CHV/BXT restrictions manually all over the
visitor. The same mechanism is leveraged to lower unsupported type
conversions easily, which obsoletes the lower_conversions pass.
v2: Give conditional modifiers the same treatment as predicates for
SEL instructions in lower_dst_modifiers() (Iago). Special-case a
couple of other instructions with inconsistent conditional mod
semantics in lower_dst_modifiers() (Curro).
Reviewed-by: Iago Toral Quiroga <itoral@igalia.com>
