[Mesa-dev] [PATCH 18/29] i965/fs: Import image access validity checks.

[Francisco Jerez]

These utility functions check whether an image access is valid.
According to the spec an invalid image access should have no effect on
the image and yield well-defined results.  Typically the hardware
implements correct bounds and surface checking by itself, but in some
cases (typed atomics on IVB and untyped messages elsewhere) we need to
implement it in software to work around lacking hardware support.

v2: Drop VEC4 suport.
---
 .../drivers/dri/i965/brw_fs_surface_builder.cpp    | 55 ++++++++++++++++++++++
 1 file changed, 55 insertions(+)

diff --git a/src/mesa/drivers/dri/i965/brw_fs_surface_builder.cpp b/src/mesa/drivers/dri/i965/brw_fs_surface_builder.cpp
index 96228dc..ed67cfc 100644
--- a/src/mesa/drivers/dri/i965/brw_fs_surface_builder.cpp
+++ b/src/mesa/drivers/dri/i965/brw_fs_surface_builder.cpp
@@ -510,3 +510,58 @@ namespace brw {
       }
    }
 }
+
+namespace {
+   namespace image_validity {
+      /**
+       * Check whether there is an image bound at the given index and write
+       * the comparison result to f0.0.  Returns an appropriate predication
+       * mode to use on subsequent image operations.
+       */
+      brw_predicate
+      emit_surface_check(const fs_builder &bld, const fs_reg &image)
+      {
+         const brw_device_info *devinfo = bld.devinfo;
+         const fs_reg size = offset(image, BRW_IMAGE_PARAM_SIZE_OFFSET);
+
+         if (devinfo->gen == 7 && !devinfo->is_haswell) {
+            /* Check the first component of the size field to find out if the
+             * image is bound.  Necessary on IVB for typed atomics because
+             * they don't seem to respect null surfaces and will happily
+             * corrupt or read random memory when no image is bound.
+             */
+            bld.CMP(bld.null_reg_ud(),
+                    retype(size, BRW_REGISTER_TYPE_UD),
+                    fs_reg(0), BRW_CONDITIONAL_NZ);
+
+            return BRW_PREDICATE_NORMAL;
+         } else {
+            /* More recent platforms implement compliant behavior when a null
+             * surface is bound.
+             */
+            return BRW_PREDICATE_NONE;
+         }
+      }
+
+      /**
+       * Check whether the provided coordinates are within the image bounds
+       * and write the comparison result to f0.0.  Returns an appropriate
+       * predication mode to use on subsequent image operations.
+       */
+      brw_predicate
+      emit_bounds_check(const fs_builder &bld, const fs_reg &image,
+                        const fs_reg &addr, unsigned dims)
+      {
+         const fs_reg size = offset(image, BRW_IMAGE_PARAM_SIZE_OFFSET);
+
+         for (unsigned c = 0; c < dims; ++c)
+            exec_predicate(c == 0 ? BRW_PREDICATE_NONE : BRW_PREDICATE_NORMAL,
+                           bld.CMP(bld.null_reg_ud(),
+                                   offset(retype(addr, BRW_REGISTER_TYPE_UD), c),
+                                   offset(size, c),
+                                   BRW_CONDITIONAL_L));
+
+         return BRW_PREDICATE_NORMAL;
+      }
+   }
+}
-- 
2.3.5