[Mesa-dev] [PATCH v2] glsl: fix variable ordering in the output_read_remover
idr at freedesktop.org
Wed Apr 4 16:12:35 PDT 2012
On 04/04/2012 07:33 AM, Vadim Girlin wrote:
> Use the hash of the variable name instead of the pointer value.
> Signed-off-by: Vadim Girlin<vadimgirlin at gmail.com>
> v2: Added the comment for the hash function as suggested by Vincent Lejeune.
> Added const qualifier and modified the cast as suggested by Tolga Dalman.
> src/glsl/lower_output_reads.cpp | 15 ++++++++++++++-
> 1 files changed, 14 insertions(+), 1 deletions(-)
> diff --git a/src/glsl/lower_output_reads.cpp b/src/glsl/lower_output_reads.cpp
> index 415b541..0427f0d 100644
> --- a/src/glsl/lower_output_reads.cpp
> +++ b/src/glsl/lower_output_reads.cpp
> @@ -54,11 +54,24 @@ public:
> virtual ir_visitor_status visit_leave(class ir_function_signature *);
> + * Hash function for the output variables - computes the hash of the name.
> + * NOTE: We're using the name string to ensure that the hash doesn't depend
> + * on any random factors, otherwise the output_read_remover could produce
> + * the random order of the assignments.
> + */
> +static unsigned
> +hash_table_var_hash(const void *key)
> + const ir_variable * var = static_cast<const ir_variable *>(key);
> + return hash_table_string_hash(var->name);
We don't usually use the name as the hashkey because you can have
multiple distinct variables with the same name. These can be variables
from different scopes or compiler-generated names (though we try to
generate unique names in that case). Since this pass only applies to
shader outputs, I don't think this problem can occur. Shader outputs
should have unique names.
My main concern is that someone may see this code in the future and copy
it in a situation where it is not safe. With the addition of some
comment that describes this,
Reviewed-by: Ian Romanick <ian.d.romanick at intel.com>
> mem_ctx = ralloc_context(NULL);
> replacements =
> - hash_table_ctor(0, hash_table_pointer_hash, hash_table_pointer_compare);
> + hash_table_ctor(0, hash_table_var_hash, hash_table_pointer_compare);
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