[Mesa-dev] [PATCH] glsl: Fix a bug where LHS swizzles of swizzles were too small.

Kenneth Graunke kenneth at whitecape.org
Wed Jul 22 21:39:23 PDT 2015

A simple shader such as

   vec4 color;
   color.xy.x = 1.0;

would cause ir_assignment::set_lhs() to generate bogus IR:

   (swiz xy (swiz x (constant float (1.0))))

We were setting the number of components of each new RHS swizzle based
on the highest channel used in the LHS swizzle.  So, .xy.y would
generate (swiz xy (swiz xx ...)), while .xy.x would break.

Our existing Piglit test happened to use .xzy.z, which worked, since
'z' is the third component, resulting in an xxx swizzle.

This patch sets the number of swizzle components based on the size of
the LHS swizzle's inner value, so we always have the correct number
at each step.

Fixes new Piglit tests glsl-vs-swizzle-swizzle-lhs-[23].
Fixes ir_validate assertions in in Metro 2033 Redux.

Cc: idr at freedesktop.org
Cc: mesa-stable at lists.freedesktop.org
Signed-off-by: Kenneth Graunke <kenneth at whitecape.org>
 src/glsl/ir.cpp | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/src/glsl/ir.cpp b/src/glsl/ir.cpp
index 8fb7ca4..7350dfa 100644
--- a/src/glsl/ir.cpp
+++ b/src/glsl/ir.cpp
@@ -95,6 +95,8 @@ ir_assignment::set_lhs(ir_rvalue *lhs)
 	 write_mask |= (((this->write_mask >> i) & 1) << c);
 	 update_rhs_swizzle(rhs_swiz, i, c);
+         assert(rhs_swiz.num_components <= swiz->val->type->vector_elements);
+         rhs_swiz.num_components = swiz->val->type->vector_elements;
       this->write_mask = write_mask;

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