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i965/vs: When asked to make a dst_reg for a src.xxxx, just write to src.x.

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We have several places in our pull constant handling where we make a
temporary src_reg for an int, and then turn it into a dst.  In doing so,
we were writing to the dst.xyzw, so we never register coalesced it with a
later mov from dst.x to real_dst.x.

These extra channels written would be removed if we had channel-wise DCE
in the backend, but we don't.  Fix it for now by just not writing these
extra channels that won't get used.

Reviewed-by: Matt Turner <mattst88@gmail.com>
This commit is contained in:
Eric Anholt 2013-04-04 16:30:49 -07:00
parent 007a88ed24
commit 3badbf7f7f
1 changed files with 8 additions and 1 deletions
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9
src/mesa/drivers/dri/i965/brw_vec4.cpp
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@ -200,7 +200,14 @@ dst_reg::dst_reg(src_reg reg)
this->reg = reg.reg;
this->reg_offset = reg.reg_offset;
this->type = reg.type;
this->writemask = WRITEMASK_XYZW;
/* How should we do writemasking when converting from a src_reg? It seems
* pretty obvious that for src.xxxx the caller wants to write to src.x, but
* what about for src.wx? Just special-case src.xxxx for now.
*/
if (reg.swizzle == BRW_SWIZZLE_XXXX)
this->writemask = WRITEMASK_X;
else
this->writemask = WRITEMASK_XYZW;
this->reladdr = reg.reladdr;
this->fixed_hw_reg = reg.fixed_hw_reg;
}