[Mesa-dev] [PATCH 2/2] i965/fs: Lower arithmetic instructions with register regions of unsupported width.

[Francisco Jerez]

This extends the SIMD lowering pass to enforce the hardware limitation
that no directly-addressed source may read more than 2 physical GRFs.
One can easily go over this limit when doing 64-bit arithmetic
(e.g. FP64 or extended-precision integer MULs) or SIMD32, so it's nice
to be able to just emit an instruction of the intended execution size
from the visitor and let the lowering pass deal with this restriction
transparently.

Some hardware arithmetic instructions are not handled here, including
all instructions that use the accumulator implicitly (which the SIMD
lowering pass deliberately doesn't handle), instructions with
non-per-channel sources (e.g. LINE or PLANE) and SEND-like
instructions, which need special handling most likely as virtual
opcodes.
---
 src/mesa/drivers/dri/i965/brw_fs.cpp | 62 ++++++++++++++++++++++++++++++++++++
 1 file changed, 62 insertions(+)

diff --git a/src/mesa/drivers/dri/i965/brw_fs.cpp b/src/mesa/drivers/dri/i965/brw_fs.cpp
index f9773bd..fa5ed4f 100644
--- a/src/mesa/drivers/dri/i965/brw_fs.cpp
+++ b/src/mesa/drivers/dri/i965/brw_fs.cpp
@@ -4130,6 +4130,68 @@ get_lowered_simd_width(const struct brw_device_info *devinfo,
                        const fs_inst *inst)
 {
    switch (inst->opcode) {
+   case BRW_OPCODE_MOV:
+   case BRW_OPCODE_SEL:
+   case BRW_OPCODE_NOT:
+   case BRW_OPCODE_AND:
+   case BRW_OPCODE_OR:
+   case BRW_OPCODE_XOR:
+   case BRW_OPCODE_SHR:
+   case BRW_OPCODE_SHL:
+   case BRW_OPCODE_ASR:
+   case BRW_OPCODE_CMP:
+   case BRW_OPCODE_CMPN:
+   case BRW_OPCODE_CSEL:
+   case BRW_OPCODE_F32TO16:
+   case BRW_OPCODE_F16TO32:
+   case BRW_OPCODE_BFREV:
+   case BRW_OPCODE_BFE:
+   case BRW_OPCODE_BFI1:
+   case BRW_OPCODE_BFI2:
+   case BRW_OPCODE_ADD:
+   case BRW_OPCODE_MUL:
+   case BRW_OPCODE_AVG:
+   case BRW_OPCODE_FRC:
+   case BRW_OPCODE_RNDU:
+   case BRW_OPCODE_RNDD:
+   case BRW_OPCODE_RNDE:
+   case BRW_OPCODE_RNDZ:
+   case BRW_OPCODE_LZD:
+   case BRW_OPCODE_FBH:
+   case BRW_OPCODE_FBL:
+   case BRW_OPCODE_CBIT:
+   case BRW_OPCODE_SAD2:
+   case BRW_OPCODE_MAD:
+   case BRW_OPCODE_LRP:
+   case SHADER_OPCODE_RCP:
+   case SHADER_OPCODE_RSQ:
+   case SHADER_OPCODE_SQRT:
+   case SHADER_OPCODE_EXP2:
+   case SHADER_OPCODE_LOG2:
+   case SHADER_OPCODE_POW:
+   case SHADER_OPCODE_INT_QUOTIENT:
+   case SHADER_OPCODE_INT_REMAINDER:
+   case SHADER_OPCODE_SIN:
+   case SHADER_OPCODE_COS: {
+      /* According to the PRMs:
+       *  "A. In Direct Addressing mode, a source cannot span more than 2
+       *      adjacent GRF registers.
+       *   B. A destination cannot span more than 2 adjacent GRF registers."
+       *
+       * Look for the source or destination with the largest register region
+       * which is the one that is going to limit the overal execution size of
+       * the instruction due to this rule.
+       */
+      unsigned reg_count = inst->regs_written;
+
+      for (unsigned i = 0; i < inst->sources; i++)
+         reg_count = MAX2(reg_count, (unsigned)inst->regs_read(i));
+
+      /* Calculate the maximum execution size of the instruction based on the
+       * factor by which it goes over the hardware limit of 2 GRFs.
+       */
+      return inst->exec_size / DIV_ROUND_UP(reg_count, 2);
+   }
    case SHADER_OPCODE_MULH:
       /* MULH is lowered to the MUL/MACH sequence using the accumulator, which
        * is 8-wide on Gen7+.
-- 
2.4.6