[all-commits] [llvm/llvm-project] e3d8eb: [llvm-dwarfdump][Statistics] Handle LTO cases with...

[Djordje Todorovic via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: e3d8ebe158562fb945d473319f4f5c2de25a9a02
      https://github.com/llvm/llvm-project/commit/e3d8ebe158562fb945d473319f4f5c2de25a9a02
  Author: Djordje Todorovic <djordje.todorovic at syrmia.com>
  Date:   2021-11-24 (Wed, 24 Nov 2021)

  Changed paths:
    A llvm/test/tools/llvm-dwarfdump/X86/LTO_CCU_zero_loc_cov.ll
    M llvm/tools/llvm-dwarfdump/Statistics.cpp

  Log Message:
  -----------
  [llvm-dwarfdump][Statistics] Handle LTO cases with cross CU referencing

With link-time optimizations enabled, resulting DWARF mayend up containing
cross CU references (through the DW_AT_abstract_origin attribute).
Consider the following example:

// sum.c
__attribute__((always_inline)) int sum(int a, int b)
{
     return a + b;
}
// main.c
extern int sum(int, int);
int main()
{
     int a = 5, b = 10, c = sum(a, b);
     return 0;
}

Compiled as follows:

$ clang -g -flto -fuse-ld=lld main.c sum.c -o main

Results in the following DWARF:

-- sum.c CU: abstract instance tree
...
0x000000b0:   DW_TAG_subprogram
                DW_AT_name	("sum")
                DW_AT_decl_file	("sum.c")
                DW_AT_decl_line	(1)
                DW_AT_prototyped	(true)
                DW_AT_type	(0x000000d3 "int")
                DW_AT_external	(true)
                DW_AT_inline	(DW_INL_inlined)

0x000000bc:     DW_TAG_formal_parameter
                  DW_AT_name	("a")
                  DW_AT_decl_file	("sum.c")
                  DW_AT_decl_line	(1)
                  DW_AT_type	(0x000000d3 "int")

0x000000c7:     DW_TAG_formal_parameter
                  DW_AT_name	("b")
                  DW_AT_decl_file	("sum.c")
                  DW_AT_decl_line	(1)
                  DW_AT_type	(0x000000d3 "int")
...
-- main.c CU: concrete inlined instance tree
...
0x0000006d:     DW_TAG_inlined_subroutine
                  DW_AT_abstract_origin	(0x00000000000000b0 "sum")
                  DW_AT_low_pc	(0x00000000002016ef)
                  DW_AT_high_pc	(0x00000000002016f1)
                  DW_AT_call_file	("main.c")
                  DW_AT_call_line	(5)
                  DW_AT_call_column	(0x19)

0x00000081:       DW_TAG_formal_parameter
                    DW_AT_location	(DW_OP_reg0 RAX)
                    DW_AT_abstract_origin	(0x00000000000000bc "a")

0x00000088:       DW_TAG_formal_parameter
                    DW_AT_location	(DW_OP_reg2 RCX)
                    DW_AT_abstract_origin	(0x00000000000000c7 "b")
...

Note that each entry within the concrete inlined instance tree in
the main.c CU has a DW_AT_abstract_origin attribute which
refers to a corresponding entry within the abstract instance
tree in the sum.c CU.
llvm-dwarfdump --statistics did not properly report
DW_TAG_formal_parameters/DW_TAG_variables from concrete inlined
instance trees which had 0% location coverage and which
referred to a different CU, mainly because information about abstract
instance trees and their parameters/variables was stored
locally - just for the currently processed CU,
rather than globally - for all CUs.
In particular, if the concrete inlined instance tree from
the example above was to look like this
(i.e. parameter b has 0% location coverage, hence why it's missing):

0x0000006d:     DW_TAG_inlined_subroutine
                  DW_AT_abstract_origin	(0x00000000000000b0 "sum")
                  DW_AT_low_pc	(0x00000000002016ef)
                  DW_AT_high_pc	(0x00000000002016f1)
                  DW_AT_call_file	("main.c")
                  DW_AT_call_line	(5)
                  DW_AT_call_column	(0x19)

0x00000081:       DW_TAG_formal_parameter
                    DW_AT_location	(DW_OP_reg0 RAX)
                    DW_AT_abstract_origin	(0x00000000000000bc "a")

llvm-dwarfdump --statistics would have not reported b as such.

Patch by Dimitrije Milosevic.

Differential revision: https://reviews.llvm.org/D113465