[Mesa-dev] [PATCHv4 32/32] i965: Don't compact instructions with unmapped bits.

[Francisco Jerez]

Some instruction bits don't have a mapping defined to any compacted
instruction field.  If they're ever set and we end up compacting the
instruction they will be forced to zero.  Avoid using compaction in such
cases.

v2: Align multiple lines of an expression to the same column.  Change
    conditional compaction of 3-source instructions to an
    assertion. (Matt)
v3: The 3-source instruction bit 105 is part of SourceIndex on CHV.
    Add assertion that reserved bit 7 is not set. (Matt)
    Document overlap with UIP and 64-bit immediate fields.
v4: Make some more unmapped bit checks assertions. (Matt)
---
 src/mesa/drivers/dri/i965/brw_eu_compact.c | 53 ++++++++++++++++++++++++++++++
 1 file changed, 53 insertions(+)

diff --git a/src/mesa/drivers/dri/i965/brw_eu_compact.c b/src/mesa/drivers/dri/i965/brw_eu_compact.c
index 8e33bcb..26c41ea 100644
--- a/src/mesa/drivers/dri/i965/brw_eu_compact.c
+++ b/src/mesa/drivers/dri/i965/brw_eu_compact.c
@@ -843,11 +843,61 @@ set_3src_source_index(struct brw_context *brw, brw_compact_inst *dst, brw_inst *
 }
 
 static bool
+has_unmapped_bits(struct brw_context *brw, brw_inst *src)
+{
+   /* Check for instruction bits that don't map to any of the fields of the
+    * compacted instruction.  The instruction cannot be compacted if any of
+    * them are set.  They overlap with:
+    *  - NibCtrl (bit 47 on Gen7, bit 11 on Gen8)
+    *  - Dst.AddrImm[9] (bit 47 on Gen8)
+    *  - Src0.AddrImm[9] (bit 95 on Gen8)
+    *  - Imm64[27:31] (bits 91-95 on Gen7, bit 95 on Gen8)
+    *  - UIP[31] (bit 95 on Gen8)
+    */
+   if (brw->gen >= 8) {
+      assert(!brw_inst_bits(src, 7,  7));
+      return brw_inst_bits(src, 95, 95) ||
+             brw_inst_bits(src, 47, 47) ||
+             brw_inst_bits(src, 11, 11);
+   } else {
+      assert(!brw_inst_bits(src, 7,  7) &&
+             !(brw->gen < 7 && brw_inst_bits(src, 90, 90)));
+      return brw_inst_bits(src, 95, 91) ||
+             brw_inst_bits(src, 47, 47);
+   }
+}
+
+static bool
+has_3src_unmapped_bits(struct brw_context *brw, brw_inst *src)
+{
+   /* Check for three-source instruction bits that don't map to any of the
+    * fields of the compacted instruction.  All of them seem to be reserved
+    * bits currently.
+    */
+   if (brw->gen >= 9 || brw->is_cherryview) {
+      assert(!brw_inst_bits(src, 127, 127) &&
+             !brw_inst_bits(src, 7,  7));
+   } else {
+      assert(brw->gen >= 8);
+      assert(!brw_inst_bits(src, 127, 126) &&
+             !brw_inst_bits(src, 105, 105) &&
+             !brw_inst_bits(src, 84, 84) &&
+             !brw_inst_bits(src, 36, 35) &&
+             !brw_inst_bits(src, 7,  7));
+   }
+
+   return false;
+}
+
+static bool
 brw_try_compact_3src_instruction(struct brw_context *brw, brw_compact_inst *dst,
                                  brw_inst *src)
 {
    assert(brw->gen >= 8);
 
+   if (has_3src_unmapped_bits(brw, src))
+      return false;
+
 #define compact(field) \
    brw_compact_inst_set_3src_##field(dst, brw_inst_3src_##field(brw, src))
 
@@ -937,6 +987,9 @@ brw_try_compact_instruction(struct brw_context *brw, brw_compact_inst *dst,
       return false;
    }
 
+   if (has_unmapped_bits(brw, src))
+      return false;
+
    memset(&temp, 0, sizeof(temp));
 
    brw_compact_inst_set_opcode(&temp, brw_inst_opcode(brw, src));
-- 
2.1.3