16-bit immediates need to replicate the 16-bit immediate value
in both words of the 32-bit value. This needs to be careful
to avoid sign-extension, which the previous implementation was
not handling properly.
For example, with the previous implementation, storing the value
-3 would generate imm.d = 0xfffffffd due to signed integer sign
extension, which is not correct. Instead, we should cast to
uint16_t, which gives us the correct result: imm.ud = 0xfffdfffd.
We only had a couple of cases hitting this path in the driver
until now, one with value -1, which would work since all bits are
one in this case, and another with value -2 in brw_clip_tri(),
which would hit the aforementioned issue (this case only affects
gen4 although we are not aware of whether this was causing an
actual bug somewhere).
v2: Make explicit uint32_t casting for left shift (Jason Ekstrand)
Reviewed-by: Jason Ekstrand <ja...@jlekstrand.net>
Cc: "18 . 0 18 . 1" <mesa-sta...@lists.freedesktop.org>
---
src/intel/compiler/brw_reg.h | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/src/intel/compiler/brw_reg.h b/src/intel/compiler/brw_reg.h
index dff9b970b2f..ac12ab3d2dd 100644
--- a/src/intel/compiler/brw_reg.h
+++ b/src/intel/compiler/brw_reg.h
@@ -705,7 +705,7 @@ static inline struct brw_reg
brw_imm_w(int16_t w)
{
struct brw_reg imm = brw_imm_reg(BRW_REGISTER_TYPE_W);
- imm.d = w | (w << 16);
+ imm.ud = (uint16_t)w | (uint32_t)(uint16_t)w << 16;
return imm;
}
--
2.14.3
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