[Mesa-dev] [PATCH 2/6] i965/fs: Unrestrict constant propagation into integer multiply.
mattst88 at gmail.com
Fri May 15 14:02:05 PDT 2015
Gen8+'s MUL instruction doesn't ignore the high 16-bits of one source
like on earlier platforms, so we can constant propagate into it without
worry. Integer multiplies (not into the accumulator, which is done for
imul_high) are lowered in lower_integer_multiplication(), so it's safe
there as well.
On Broadwell, fragment shaders only:
total instructions in shared programs: 4377769 -> 4377451 (-0.01%)
instructions in affected programs: 48064 -> 47746 (-0.66%)
On Broadwell, vertex shaders only:
total instructions in shared programs: 2858885 -> 2856313 (-0.09%)
instructions in affected programs: 26380 -> 23808 (-9.75%)
On Broadwell, vertex shaders only (with INTEL_USE_NIR=1):
total instructions in shared programs: 2911688 -> 2865984 (-1.57%)
instructions in affected programs: 1421715 -> 1376011 (-3.21%)
src/mesa/drivers/dri/i965/brw_fs_copy_propagation.cpp | 10 +++++++++-
1 file changed, 9 insertions(+), 1 deletion(-)
diff --git a/src/mesa/drivers/dri/i965/brw_fs_copy_propagation.cpp b/src/mesa/drivers/dri/i965/brw_fs_copy_propagation.cpp
index 52bfa92..c92aae4 100644
@@ -541,8 +541,16 @@ fs_visitor::try_constant_propagate(fs_inst *inst, acp_entry *entry)
/* Fit this constant in by commuting the operands.
* Exception: we can't do this for 32-bit integer MUL/MACH
* because it's asymmetric.
+ * The BSpec says for Broadwell that
+ * "When multiplying DW x DW, the dst cannot be accumulator."
+ * Integer MUL with a non-accumulator destination will be lowered
+ * by lower_integer_multiplication(), so don't restrict it.
- if ((inst->opcode == BRW_OPCODE_MUL ||
+ if (((inst->opcode == BRW_OPCODE_MUL &&
+ inst->dst.is_accumulator()) ||
inst->opcode == BRW_OPCODE_MACH) &&
(inst->src.type == BRW_REGISTER_TYPE_D ||
inst->src.type == BRW_REGISTER_TYPE_UD))
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