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| -rw-r--r-- | src/mesa/drivers/dri/i965/brw_eu_compact.c | 35 |
1 files changed, 35 insertions, 0 deletions
diff --git a/src/mesa/drivers/dri/i965/brw_eu_compact.c b/src/mesa/drivers/dri/i965/brw_eu_compact.c index 50420deb47d..114d18f4ab2 100644 --- a/src/mesa/drivers/dri/i965/brw_eu_compact.c +++ b/src/mesa/drivers/dri/i965/brw_eu_compact.c @@ -35,6 +35,41 @@ * The idea of instruction compaction is that most instructions use a tiny * subset of the GPU functionality, so we can encode what would be a 16 byte * instruction in 8 bytes using some lookup tables for various fields. + * + * + * Instruction compaction capabilities vary subtly by generation. + * + * G45's support for instruction compaction is very limited. Jump counts on + * this generation are in units of 16-byte uncompacted instructions. As such, + * all jump targets must be 16-byte aligned. Also, all instructions must be + * naturally aligned, i.e. uncompacted instructions must be 16-byte aligned. + * A G45-only instruction, NENOP, must be used to provide padding to align + * uncompacted instructions. + * + * Gen5 removes these restrictions and changes jump counts to be in units of + * 8-byte compacted instructions, allowing jump targets to be only 8-byte + * aligned. Uncompacted instructions can also be placed on 8-byte boundaries. + * + * Gen6 adds the ability to compact instructions with a limited range of + * immediate values. Compactable immediates have 12 unrestricted bits, and a + * 13th bit that's replicated through the high 20 bits, to create the 32-bit + * value of DW3 in the uncompacted instruction word. + * + * On Gen7 we can compact some control flow instructions with a small positive + * immediate in the low bits of DW3, like ENDIF with the JIP field. Other + * control flow instructions with UIP cannot be compacted, because of the + * replicated 13th bit. No control flow instructions can be compacted on Gen6 + * since the jump count field is not in DW3. + * + * break JIP/UIP + * cont JIP/UIP + * halt JIP/UIP + * if JIP/UIP + * else JIP (plus UIP on BDW+) + * endif JIP + * while JIP (must be negative) + * + * Gen 8 adds support for compacting 3-src instructions. */ #include "brw_context.h" |