- return new(ctx) ir_swizzle(deref->array,
- ir_constant->value.i[0], 0, 0, 0, 1);
+
+ /* Page 40 of the GLSL 1.20 spec says:
+ *
+ * "When indexing with non-constant expressions, behavior is undefined
+ * if the index is negative, or greater than or equal to the size of
+ * the vector."
+ *
+ * The quoted spec text mentions non-constant expressions, but this code
+ * operates on constants. These constants are the result of non-constant
+ * expressions that have been optimized to constants. The common case here
+ * is a loop counter from an unrolled loop that is used to index a vector.
+ *
+ * The ir_swizzle constructor gets angry if the index is negative or too
+ * large. For simplicity sake, just clamp the index to [0, size-1].
+ */
+ const int i = CLAMP(idx->value.i[0], 0,
+ (int) expr->operands[0]->type->vector_elements - 1);
+
+ return new(ctx) ir_swizzle(expr->operands[0], i, 0, 0, 0, 1);