glsl: fix constructing a vector from a matrix

Without this patch, the following constructs (not an extensive list)
would crash mesa:

- mat2 foo = mat2(1); vec4 bar = vec4(foo);
- mat3 foo = mat3(1); vec4 bar = vec4(foo);
- mat3 foo = mat3(1); ivec4 bar = ivec4(foo);

The first case is explicitely allowed by the GLSL spec, as seen on
page 101 of the GLSL 4.40 spec:

	"vec4(mat2) // the vec4 is column 0 followed by column 1"

The other cases are implicitely allowed also.

The actual changes are quite minimal. We first split each column of
the matrix to a list of vectors and then use them to initialize the
vector. An additional check to make sure that we are not trying to
copy 0 elements of a vector fix the (i)vec4(mat3) case as the last
vector (3rd column) is not needed at all.

Reviewed-by: Tapani Pälli <tapani.palli@intel.com>
Signed-off-by: Martin Peres <martin.peres@linux.intel.com>

src/glsl/ast_function.cpp

@@ -993,11 +993,15 @@ emit_inline_vector_constructor(const glsl_type *type,
    ir_variable *var = new(ctx) ir_variable(type, "vec_ctor", ir_var_temporary);
    instructions->push_tail(var);
 
-   /* There are two kinds of vector constructors.
+   /* There are three kinds of vector constructors.
     *
     *  - Construct a vector from a single scalar by replicating that scalar to
     *    all components of the vector.
     *
+    *  - Construct a vector from at least a matrix. This case should already
+    *    have been taken care of in ast_function_expression::hir by breaking
+    *    down the matrix into a series of column vectors.
+    *
     *  - Construct a vector from an arbirary combination of vectors and
     *    scalars.  The components of the constructor parameters are assigned
     *    to the vector in order until the vector is full.
@@ -1091,6 +1095,14 @@ emit_inline_vector_constructor(const glsl_type *type,
 	    rhs_components = lhs_components - base_component;
 	 }
 
+	 /* If we do not have any components left to copy, break out of the
+	  * loop. This can happen when initializing a vec4 with a mat3 as the
+	  * mat3 would have been broken into a series of column vectors.
+	  */
+	 if (rhs_components == 0) {
+	    break;
+	 }
+
 	 const ir_constant *const c = param->as_constant();
 	 if (c == NULL) {
 	    /* Mask of fields to be written in the assignment.
@@ -1681,11 +1693,11 @@ ast_function_expression::hir(exec_list *instructions,
 	 return ir_rvalue::error_value(ctx);
       }
 
-      /* Later, we cast each parameter to the same base type as the
-       * constructor.  Since there are no non-floating point matrices, we
-       * need to break them up into a series of column vectors.
+      /* Matrices can never be consumed as is by any constructor but matrix
+       * constructors. If the constructor type is not matrix, always break the
+       * matrix up into a series of column vectors.
        */
-      if (constructor_type->base_type != GLSL_TYPE_FLOAT) {
+      if (!constructor_type->is_matrix()) {
 	 foreach_in_list_safe(ir_rvalue, matrix, &actual_parameters) {
 	    if (!matrix->type->is_matrix())
 	       continue;