PR41343 testcase lead me to look at 3 small testcases showing VTA throwing debug info on the floor (-gdwarf-4 -O2 in all cases): int foo (int i, int j) { int i1 = 2 * i; int i2 = 3 * i; return j; } Above is a problem already during RTL expansion, SSA_NAME i_1 (of PARM_DECL i, with GIMPLE_NOP in SSA_NAME_DEF_STMT) is expanded to NULL by expand_debug_expr, because var_to_partition returns NO_PARTITION for it. I think we could special case the initial SSA_NAMEs of parameters and expand them as the parameters.
int i = 1, j; int foo (void) { int i1 = 2 * i; int i2 = 3 * i; return j; } In this case we emit i2 debug info correctly: .byte 0x3 # DW_OP_addr .quad i .byte 0x6 # DW_OP_deref .byte 0x33 # DW_OP_lit3 .byte 0x1e # DW_OP_mul .byte 0x9f # DW_OP_stack_value .byte 0x93 # DW_OP_piece .uleb128 0x4 but i1 is lost (has empty location list). In *.compgotos things look still good to me: (debug_insn 5 2 6 2 d.c:6 (var_location:SI i1 (mult:SI (mem/c/i:SI (symbol_ref:DI ("i") [flags 0x2] <var_decl 0x7f36e4772820 i>) [2 i+0 S4 A32]) (const_int 2 [0x2]))) -1 (nil)) (debug_insn 6 5 12 2 d.c:7 (var_location:SI i2 (mult:SI (mem/c/i:SI (symbol_ref:DI ("i") [flags 0x2] <var_decl 0x7f36e4772820 i>) [2 i+0 S4 A32]) (const_int 3 [0x3]))) -1 (nil)) are the only places where i1 and i2 are mentioned. But var-tracking messes it up: (note 24 2 23 2 (var_location i1 (expr_list:REG_DEP_TRUE (ashift:SI (mem/c/i:SI (symbol_ref:DI ("i") [flags 0x2] <var_decl 0x7f36e4772820 i>) [2 i+0 S4 A32]) (const_int 1 [0x1])) (const_int 0 [0x0]))) NOTE_INSN_VAR_LOCATION) (note 23 24 25 2 (var_location i1 (nil)) NOTE_INSN_VAR_LOCATION) (note 25 23 12 2 (var_location i2 (expr_list:REG_DEP_TRUE (mult:SI (mem/c/i:SI (symbol_ref:DI ("i") [flags 0x2] <var_decl 0x7f36e4772820 i>) [2 i+0 S4 A32]) (const_int 3 [0x3])) (const_int 0 [0x0]))) NOTE_INSN_VAR_LOCATION) (note the second i1 note). And my last testcase is: int i, j; int foo (void) { int i1 = 2 * i; int i2 = 3 * i; return j; } Here info is dropped at RTL expansion time, as the VAR_DECL doesn't have RTL set yet during the expansion. It is common though, so it will be emitted in the current TU anyway. Another case would be extern int i, j; where it is questionable if the debug info should reference an external variable which wouldn't be mentioned anywhere in the TU. -- Summary: VTA missed-debug issues Product: gcc Version: 4.5.0 Status: UNCONFIRMED Severity: normal Priority: P3 Component: debug AssignedTo: unassigned at gcc dot gnu dot org ReportedBy: jakub at gcc dot gnu dot org http://gcc.gnu.org/bugzilla/show_bug.cgi?id=41353