[Mesa-dev] [PATCH] i965/fs: Factor out source components calculation to a separate method.

[Francisco Jerez]

This cleans up fs_inst::regs_read() slightly by disentangling the
calculation of "components" from the handling of message payload
arguments.  This will also simplify the SIMD lowering and logical send
message lowering passes, because it will avoid expressions like
'regs_read * REG_SIZE / component_size' which are not only ugly, they
may be inaccurate because regs_read rounds up the result to the
closest register multiple so they could give incorrect results when
the component size is lower than one register (e.g. uniforms).  This
didn't seem to be a problem right now because all such expressions
happen to be dealing with per-channel GRFs only currently, but that's
by no means obvious so better be safe than sorry.
---
 src/mesa/drivers/dri/i965/brw_fs.cpp  | 30 ++++++++++++++++++++----------
 src/mesa/drivers/dri/i965/brw_ir_fs.h |  1 +
 2 files changed, 21 insertions(+), 10 deletions(-)

diff --git a/src/mesa/drivers/dri/i965/brw_fs.cpp b/src/mesa/drivers/dri/i965/brw_fs.cpp
index 3f91a2b..e4e96bc 100644
--- a/src/mesa/drivers/dri/i965/brw_fs.cpp
+++ b/src/mesa/drivers/dri/i965/brw_fs.cpp
@@ -661,10 +661,26 @@ fs_inst::is_partial_write() const
            !this->dst.is_contiguous());
 }
 
+unsigned
+fs_inst::components_read(unsigned i) const
+{
+   switch (opcode) {
+   case FS_OPCODE_LINTERP:
+   case FS_OPCODE_PIXEL_X:
+   case FS_OPCODE_PIXEL_Y:
+      if (i == 0)
+         return 2;
+      else
+         return 1;
+
+   default:
+      return 1;
+   }
+}
+
 int
 fs_inst::regs_read(int arg) const
 {
-   unsigned components = 1;
    switch (opcode) {
    case FS_OPCODE_FB_WRITE:
    case SHADER_OPCODE_URB_WRITE_SIMD8:
@@ -686,15 +702,8 @@ fs_inst::regs_read(int arg) const
       break;
 
    case FS_OPCODE_LINTERP:
-      if (arg == 0)
-         return exec_size / 4;
-      else
+      if (arg == 1)
          return 1;
-
-   case FS_OPCODE_PIXEL_X:
-   case FS_OPCODE_PIXEL_Y:
-      if (arg == 0)
-         components = 2;
       break;
 
    case SHADER_OPCODE_LOAD_PAYLOAD:
@@ -718,7 +727,8 @@ fs_inst::regs_read(int arg) const
       return 1;
    case GRF:
    case HW_REG:
-      return DIV_ROUND_UP(components * src[arg].component_size(exec_size),
+      return DIV_ROUND_UP(components_read(arg) *
+                          src[arg].component_size(exec_size),
                           REG_SIZE);
    case MRF:
       unreachable("MRF registers are not allowed as sources");
diff --git a/src/mesa/drivers/dri/i965/brw_ir_fs.h b/src/mesa/drivers/dri/i965/brw_ir_fs.h
index 693357f..97c6f8b 100644
--- a/src/mesa/drivers/dri/i965/brw_ir_fs.h
+++ b/src/mesa/drivers/dri/i965/brw_ir_fs.h
@@ -201,6 +201,7 @@ public:
    bool is_send_from_grf() const;
    bool is_partial_write() const;
    bool is_copy_payload(const brw::simple_allocator &grf_alloc) const;
+   unsigned components_read(unsigned i) const;
    int regs_read(int arg) const;
    bool can_do_source_mods(const struct brw_device_info *devinfo);
    bool has_side_effects() const;
-- 
2.4.3