Ping! [PATCH, revised]: Track uninitialized variables

[Caroline Tice <ctice@apple.com>]

As a point of interest:  The GDB side of this patch has been accepted  
and
committed to FSF GDB.

-- Caroline

On May 11, 2007, at 12:13 PM, Caroline Tice wrote:

> Here is a revised version of my patch for tracking uninitialized
> variables (see description in original posting copied below).  I added
> the comments Ian asked for, and I changed the way it is turned on/off.
> Instead of the macro in my previous patch, it is now controlled by a
> command line option, -fvar-tracking-uninit, which turns on
> var-tracking, just like -fvar-tracking, but also turns on the
> uninitialized variable tracking.  I added the same feasibility  
> checks to
> it that are used for -fvar-tracking.  I also turned it on by default
> on darwin systems running 10.5 or later (when var-tracking is on).
>
> I tested this patch by bootstrapping it and running the dejagnu
> testsuite without any regressions, on a ppc running apple-darwin, an
> x86 running apple-darwin, and an x86 64 running 64-bit linux.  I also
> ran it on a small test case containing uninitialized variables, to
> verify that it turns on when the command line option is passed, or
> when running on the correct version of darwin, and is off at all other
> times.
>
> Is this patch okay to commit to mainline?
>
> --Caroline Tice
> ctice@apple.com
>
>
> On May 1, 2007, at 5:02 PM, Caroline Tice wrote:
>
>>
>> As part of some work I've been doing on improving debugging of
>> optimized code, I have developed the following patch which, while
>> tracking the locations of variables, also keeps track of whether the
>> variables are initialized or not (it makes conservative assumptions
>> where it can't be sure).  For those places where it is sure the
>> variables are unintialized, it adds an annotation to the
>> var_location_note, which the dwarf writer later translates to a new
>> DW_OP (an extension) that indicates a variable is uninitialized
>> (DW_OP_GNU_uninit).
>
>> Since this work requires that GDB be able to read and do something
>> reasonable with the new DW_OP, I have also created a GDB patch to  
>> deal
>> with the new op, and to inform the user that a particular value is
>> unintialized when the user asks to see it.  As the two patches really
>> go together, I am attaching both of them to this message.  (I will
>> also be sending the GDB patch to the gdb patches list).
>
>> Because using the new DW_OP is sensitive to whether or not the user
>> has a version of GDB that can handle it, I have added a macro,
>> TARGET_DWARF_UNINIT_VARS, which defaults to 0, and which controls
>> whether the uninitialized variable tracking is done.
>
>> I have bootstrapped and run the dejagnu testsuite on this patch, with
>> no regressions, on a ppc running apple-darwin, an x86 running
>> apple-darwin, and an x86 64 running 64-bit linux.
>
>> Is this patch okay to commit to mainline?
>> -- Caroline Tice
>> ctice@apple.com
>>
>
> 2007-05-11  Caroline Tice  <ctice@apple.com>
>
>        * toplev.c (process_options): Turn flag_var_tracking_uninit  
> off when
>        flag_var_tracking is explicitly turned off (i.e. when variable
>        tracking is not feasible); otherwise, turn flag_var_tracking  
> on when
>        flag_var_tracking_uninit is on.
>        * rtl.def (VAR_LOCATION): Add a new integer subfield to  
> VAR_LOCATION
>        note definitions, to allow recording of initialization status  
> in the
>        notes.
>        * dwarf2out.c (dwarf_stack_op_name): Add case for  
> DW_OP_GNU_uninit.
>        (add_var_loc_to_decl): Add comparison of  
> NOTE_VAR_LOCATION_STATUS to
>        determine if two note locations are equal.
>        (output_loc_list): Don't output list entries whose start &  
> end labels
>        are the same.
>        (reg_loc_descriptor): Add parameter for initialization  
> status; pass it
>        to other loc descriptor functions.
>        (one_reg_loc_descriptor): Add parameter for initialization  
> status;
>        check its value and add DW_OP_GNU_uninit to returned loc  
> descr if
>        appropriate.
>        (multiple_reg_loc_descriptor): Add parameter for initialization
>        status;
>        pass init status argument to other loc descriptor functions;  
> check
>        value of intialization parameter and add DW_OP_GNU_uninit to  
> returned
>        loc descr if appropriate.
>        (based_loc_descr): Add parameter for initialization status;  
> add new
>        variable for return value; check value of initialization  
> parameter and
>        add DW_OP_GNU_uninit to returned loc descr if appropriate.
>        (concatn_mem_loc_descriptor): Add parameter for  
> initialization status;
>        pass init status argument to other loc descriptor functions;  
> check
>        value of intialization parameter and add DW_OP_GNU_uninit to  
> returned
>        loc descr if appropriate.
>        (mem_loc_descriptor): Likewise.
>        (concat_loc_descriptor): Likewise.
>        (concatn_loc_descriptor): Likewise.
>        (loc_descriptor): Add parameter for initialization status;  
> pass it as
>        argument to other loc descriptor function calls.
>        (loc_descriptor_from_tree_1): Add appropriate initialization  
> status
>        to loc descriptor function calls.
>        (add_location_or_const_value_attribute): Get initialization  
> status
>        from VAR_LOCATION note; add initialization status to loc  
> descriptor
>        function calls.
>        * dwarf2.h (enum dwarf_location_atom): New op,  
> DW_OP_GNU_uninit.
>        * print-rtl.c (print_rtx): When printing a VAR_LOCATION note,  
> if
>        status is uninitialized, add "[uninint]" to output.
>        * common.opt (fvar-tracking-uninit): New option, similar to
>        fvar-tracking, to turn on tracking of uninitialized  
> variables; creates
>        a new global flag, flag_var_tracking_uninit.
>        * rtl.h (NOTE_VAR_LOCATION_STATUS): New macro for accessing  
> new field.
>        (enum var_init_status): New type, for var initialization  
> status field.
>        * var-tracking.c (struct location_chain_def): Two new fields,  
> init,
>        for initialization status, and set_src for the assignment  
> value expr.
>        (unshare_variable): New parameter for initialization status;
>        initialize new init and set_src fields.
>        (var_reg_set): New parameters for initialization status and  
> value;
>        pass them to set_variable_part.
>        (var_mem_set): Likewise.
>        (get_init_value): New function.
>        (var_reg_delete_and_set): New initialization status & value
>        parameters; add call to get_init_value if status is unknown;  
> pass new
>        parameters to clobber_variable_part and var_reg_set.
>        (var_mem_delete_and_set): Likewise.
>        (var_reg_delete): Pass null set_src value to  
> clobber_variable_part.
>        (var_mem_delete): Likewise.
>        (variable_union): Pass status to unshare_variable; initialize  
> new init
>        and set_src fields.  If flag_var_tracking_uninit is not set,  
> force
>        status to initialized.
>        (add_stores): Store insn, rather than NEXT_INSN(insn), so it  
> can be
>        used later to get the set_src value.
>        (find_src_status): New function.
>        (find_src_set_src): New function.
>        (compute_bb_dataflow): Pass init status to calls to  
> var_reg_set,
>        var_mem_set, var_reg_delete_and_set and  
> var_mem_delete_and_set; for
>        MO_SET, get set_src value and pass it to   
> var_reg_delete_and_set
>        and var_mem_delete_and_set.
>        (dump_variable):  Print out "[uninit]" if appropriate.
>        (set_variable_part): Add new initialization and set_src  
> parameters;
>        pass status to unshare_variable; set node->init and node- 
> >set_src
>        fields and modify slot in hash table appropriately; save the  
> init and
>        set_src values if appropriate and assign to the new node.
>        (clobber_variable_part): New set_src parameter; if two nodes  
> have
>        same variable and same location but different set_src  
> (assignment)
>        values, clobber old node.
>        (delete_variable_part): Pass init status to unshare_variable.
>        (emit_note_insn_var_location): Add initialized var; assign  
> var's init
>        status to new 'initialized'; pass new init status field to  
> calls to
>        gen_rtx_VAR_LOCATION.  If flag_var_tracking_uninit is not  
> set, force
>        status to initialized.
>        (emit_notes_in_bb): Pass initialization status to calls to
>        var_reg_set, var_mem_set, var_reg_delete_and_set and
>        var_mem_delete_and_set; for MO_SET, get set_src value and  
> pass it to
>        var_reg_delete_and_set and var_mem_delete_and_set; call
>        emit_notes_for_changes on NEXT_INSN(insn) rather than on  
> insn, to
>        make up for change in add_stores.
>        (vt_add_function_parameters): Add status to calls to
>        set_variable_part.
>        * config/darwin.c (darwin_override_options): Turn on  
> uninitialized
>        tracking automatically, if var_tracking is on and the system is
>        10.5 or higher.
>
>
> <fsf-gcc-patch.v2.txt>