c7bac01ab4
gimplify_modify_expr_rhs has an optimization whereby the assignment to an aggregate variable from a read-only object with a DECL_INITIAL is optimized into the direct assignment of the DECL_INITIAL, provided that no temporary is created in the process. The optimization is blocked if the read-only object is volatile, which is OK as per the semantics of volatile, but also if the target variable is volatile, on the grounds that the modified assignment might end up being done on a per field basis, which is also OK. But this latter restriction is enforced a priori and there are cases where the modified assignment would be OK, for example if there is only one field or the DECL_INITIAL is equivalent to the empty CONSTRUCTOR, i.e. all zeros. So, in the latter case, the patch changes gimplify_modify_expr_rhs to ask gimplify_init_constructor whether the assignment would be done as a block, which is easy because gimplify_init_constructor knows that it must create a temporary if the LHS is volatile and this would not be the case, so it's just a matter of completing the NOTIFY_TEMP_CREATION mechanism. gcc/ChangeLog * gimplify.c (gimplify_init_constructor) <AGGREGATE_TYPE>: Declare new ENSURE_SINGLE_ACCESS constant and move variables down. If it is true and all elements are zero, then always clear. Return GS_ERROR if a temporary would be created for it and NOTIFY_TEMP_CREATION set. (gimplify_modify_expr_rhs) <VAR_DECL>: If the target is volatile but the type is aggregate non-addressable, ask gimplify_init_constructor whether it can generate a single access to the target. gcc/testsuite/ChangeLog * gnat.dg/aggr30.ads, gnat.dg/aggr30.adb: New test. |
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