[Mesa-dev] [PATCH 01/10] intel/fs: Handle source modifiers in lower_integer_multiplication().

[Francisco Jerez]

lower_integer_multiplication() implements 32x32-bit multiplication on
some platforms by bit-casting one of the 32-bit sources into two
16-bit unsigned integer portions.  This can give incorrect results if
the original instruction specified a source modifier.  Fix it by
emitting an additional MOV instruction implementing the source
modifiers where necessary.

Cc: mesa-stable at lists.freedesktop.org
---
 src/intel/compiler/brw_fs.cpp | 20 ++++++++++++++++++--
 src/intel/compiler/brw_fs.h   | 19 +++++++++++++++++++
 2 files changed, 37 insertions(+), 2 deletions(-)

diff --git a/src/intel/compiler/brw_fs.cpp b/src/intel/compiler/brw_fs.cpp
index 590a9b32a8e..2f0f0151219 100644
--- a/src/intel/compiler/brw_fs.cpp
+++ b/src/intel/compiler/brw_fs.cpp
@@ -3862,6 +3862,9 @@ fs_visitor::lower_integer_multiplication()
             high.offset = inst->dst.offset % REG_SIZE;
 
             if (devinfo->gen >= 7) {
+               if (inst->src[1].abs)
+                  lower_src_modifiers(this, block, inst, 1);
+
                if (inst->src[1].file == IMM) {
                   ibld.MUL(low, inst->src[0],
                            brw_imm_uw(inst->src[1].ud & 0xffff));
@@ -3874,6 +3877,9 @@ fs_visitor::lower_integer_multiplication()
                            subscript(inst->src[1], BRW_REGISTER_TYPE_UW, 1));
                }
             } else {
+               if (inst->src[0].abs)
+                  lower_src_modifiers(this, block, inst, 0);
+
                ibld.MUL(low, subscript(inst->src[0], BRW_REGISTER_TYPE_UW, 0),
                         inst->src[1]);
                ibld.MUL(high, subscript(inst->src[0], BRW_REGISTER_TYPE_UW, 1),
@@ -3891,6 +3897,18 @@ fs_visitor::lower_integer_multiplication()
          }
 
       } else if (inst->opcode == SHADER_OPCODE_MULH) {
+         /* According to the BDW+ BSpec page for the "Multiply Accumulate
+          * High" instruction:
+          *
+          *  "An added preliminary mov is required for source modification on
+          *   src1:
+          *      mov (8) r3.0<1>:d -r3<8;8,1>:d
+          *      mul (8) acc0:d r2.0<8;8,1>:d r3.0<16;8,2>:uw
+          *      mach (8) r5.0<1>:d r2.0<8;8,1>:d r3.0<8;8,1>:d"
+          */
+         if (devinfo->gen >= 8 && (inst->src[1].negate || inst->src[1].abs))
+            lower_src_modifiers(this, block, inst, 1);
+
          /* Should have been lowered to 8-wide. */
          assert(inst->exec_size <= get_lowered_simd_width(devinfo, inst));
          const fs_reg acc = retype(brw_acc_reg(inst->exec_size),
@@ -3906,8 +3924,6 @@ fs_visitor::lower_integer_multiplication()
              * On Gen8, the multiply instruction does a full 32x32-bit
              * multiply, but in order to do a 64-bit multiply we can simulate
              * the previous behavior and then use a MACH instruction.
-             *
-             * FINISHME: Don't use source modifiers on src1.
              */
             assert(mul->src[1].type == BRW_REGISTER_TYPE_D ||
                    mul->src[1].type == BRW_REGISTER_TYPE_UD);
diff --git a/src/intel/compiler/brw_fs.h b/src/intel/compiler/brw_fs.h
index 163c0008820..53d9b6ce7bf 100644
--- a/src/intel/compiler/brw_fs.h
+++ b/src/intel/compiler/brw_fs.h
@@ -531,6 +531,25 @@ namespace brw {
          return fs_reg(retype(brw_vec8_grf(regs[0], 0), type));
       }
    }
+
+   /**
+    * Remove any modifiers from the \p i-th source region of the instruction,
+    * including negate, abs and any implicit type conversion to the execution
+    * type.  Instead any source modifiers will be implemented as a separate
+    * MOV instruction prior to the original instruction.
+    */
+   inline bool
+   lower_src_modifiers(fs_visitor *v, bblock_t *block, fs_inst *inst, unsigned i)
+   {
+      assert(inst->components_read(i) == 1);
+      const fs_builder ibld(v, block, inst);
+      const fs_reg tmp = ibld.vgrf(get_exec_type(inst));
+
+      ibld.MOV(tmp, inst->src[i]);
+      inst->src[i] = tmp;
+
+      return true;
+   }
 }
 
 void shuffle_from_32bit_read(const brw::fs_builder &bld,
-- 
2.19.2