[Mesa-dev] [PATCH 2/2] i965: check each field separately in backend_end::equals()

[Samuel Iglesias Gonsálvez]

Extra bits required to make room for the df field of the union don't get
initialized in all codepaths, so backend_reg comparisons done using
memcmp() can basically return random results. Check field by field to
avoid this.

Signed-off-by: Samuel Iglesias Gonsálvez <siglesias at igalia.com>
Reported-by: Francisco Jerez <currojerez at riseup.net>
---
 src/mesa/drivers/dri/i965/brw_reg.h      |  1 +
 src/mesa/drivers/dri/i965/brw_shader.cpp | 21 +++++++++++++++++++--
 2 files changed, 20 insertions(+), 2 deletions(-)

diff --git a/src/mesa/drivers/dri/i965/brw_reg.h b/src/mesa/drivers/dri/i965/brw_reg.h
index 3b76d7d..68128bd 100644
--- a/src/mesa/drivers/dri/i965/brw_reg.h
+++ b/src/mesa/drivers/dri/i965/brw_reg.h
@@ -233,6 +233,7 @@ uint32_t brw_swizzle_immediate(enum brw_reg_type type, uint32_t x, unsigned swz)
  * WM programs to implement shaders decomposed into "channel serial"
  * or "structure of array" form:
  */
+/* IMPORTANT: update backend_reg::equals() if you add a new field here. */
 struct brw_reg {
    enum brw_reg_type type:4;
    enum brw_reg_file file:3;      /* :2 hardware format */
diff --git a/src/mesa/drivers/dri/i965/brw_shader.cpp b/src/mesa/drivers/dri/i965/brw_shader.cpp
index a23f14e..7871f51 100644
--- a/src/mesa/drivers/dri/i965/brw_shader.cpp
+++ b/src/mesa/drivers/dri/i965/brw_shader.cpp
@@ -687,8 +687,25 @@ backend_shader::backend_shader(const struct brw_compiler *compiler,
 bool
 backend_reg::equals(const backend_reg &r) const
 {
-   return memcmp((brw_reg *)this, (brw_reg *)&r, sizeof(brw_reg)) == 0 &&
-          reg_offset == r.reg_offset;
+   bool equal = true;
+
+   if (this->reg_offset != r.reg_offset ||
+       this->type != r.type ||
+       this->file != r.file ||
+       this->negate != r.negate ||
+       this->abs != r.abs ||
+       this->address_mode != r.address_mode ||
+       this->pad0 != r.pad0 ||
+       this->subnr != r.subnr ||
+       this->nr != r.nr ||
+       this->ud != r.ud)
+      equal = false;
+
+   /* Check higher 32 bits of the brw_reg's union if they are filled */
+   if (equal && this->type == BRW_REGISTER_TYPE_DF && this->df != r.df)
+      equal = false;
+
+   return equal;
 }
 
 bool
-- 
2.5.0