Ping2! [PATCH, revised]: Track uninitialized variables

[Caroline Tice]

On May 18, 2007, at 12:48 PM, Caroline Tice wrote:

> 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>
>