From aa173e16a07566b7549b00946840ea16ac17a380 Mon Sep 17 00:00:00 2001 From: Paul Berry Date: Sat, 19 May 2012 08:59:36 -0700 Subject: [PATCH] glsl/constant propagation: kill whole var if LHS involves array indexing. When considering which components of a variable were killed by an assignment, constant propagation would previously just use the write mask of the assignment. This worked if the LHS of the assignment was simple, e.g.: v.xy = ...; // (assign (xy) (var_ref v) ...) But it did the wrong thing if the LHS of the assignment involved an array indexing operator, since in this case the write mask is always (x): v[i] = ...; // (assign (x) (deref_array (var_ref v) (var_ref i)) ...) In general, we can't predict which vector component will be selected by array indexing, so the only safe thing to do in this case is to kill the entire variable. Fixes piglit tests {fs,vs}-vector-indexing-kills-all-channels.shader_test. Reviewed-by: Ian Romanick Reviewed-by: Eric Anholt --- src/glsl/opt_constant_propagation.cpp | 21 ++++++++++++++++++++- 1 file changed, 20 insertions(+), 1 deletion(-) diff --git a/src/glsl/opt_constant_propagation.cpp b/src/glsl/opt_constant_propagation.cpp index d3812637df0..2601b52f6d3 100644 --- a/src/glsl/opt_constant_propagation.cpp +++ b/src/glsl/opt_constant_propagation.cpp @@ -241,7 +241,26 @@ ir_constant_propagation_visitor::visit_leave(ir_assignment *ir) if (this->in_assignee) return visit_continue; - kill(ir->lhs->variable_referenced(), ir->write_mask); + unsigned kill_mask = ir->write_mask; + if (ir->lhs->as_dereference_array()) { + /* The LHS of the assignment uses an array indexing operator (e.g. v[i] + * = ...;). Since we only try to constant propagate vectors and + * scalars, this means that either (a) array indexing is being used to + * select a vector component, or (b) the variable in question is neither + * a scalar or a vector, so we don't care about it. In the former case, + * we want to kill the whole vector, since in general we can't predict + * which vector component will be selected by array indexing. In the + * latter case, it doesn't matter what we do, so go ahead and kill the + * whole variable anyway. + * + * Note that if the array index is constant (e.g. v[2] = ...;), we could + * in principle be smarter, but we don't need to, because a future + * optimization pass will convert it to a simple assignment with the + * correct mask. + */ + kill_mask = ~0; + } + kill(ir->lhs->variable_referenced(), kill_mask); add_constant(ir); -- 2.30.2