[google/gcc-4_7] Backport patch to add line info to non-virtual thunks

[Rong Xu]

Looks good to me for google-4_7 branches.

-Rong

On Mon, Aug 6, 2012 at 5:03 PM, Cary Coutant <ccoutant@google.com> wrote:
> This patch is for the google/gcc-4_7 branch.  It backports the following
> patch from trunk at r190190:
>
>   http://gcc.gnu.org/ml/gcc-patches/2012-08/msg00321.html
>
> GCC generates non-virtual thunks directly to assembly code, which
> causes a couple of problems. First, it doesn't add source location
> information to the thunk, so the thunk simply inherits the random
> location from the end of the function in front of it (the function
> it's a thunk for). In two different compilation units compiled
> with different options, this could result in two different locations
> for the same thunk, and gold will give a false positive ODR
> violation warning.
>
> Second, if you try to compile with -S -dA, GCC crashes in final(),
> where it's trying to build a mapping from insn to bb, because the
> function has no cfg, and FOR_EACH_BB_REVERSE tries to dereference
> cfun->cfg without checking for non-NULL.
>
> Bootstrapped and ran testsuite with no regressions.
>
> Google ref b/6891766.
>
>
> 2012-08-06  Cary Coutant  <ccoutant@google.com>
>
> gcc/
>         * cgraphunit.c (assemble_thunk): Add source line info.
>         * final.c (final): Check for non-null cfg pointer.
>
> gcc/testsuite/
>         * g++.dg/debug/dwarf2/non-virtual-thunk.C: New test case.
>
>
> Index: gcc/final.c
> ===================================================================
> --- gcc/final.c (revision 190189)
> +++ gcc/final.c (working copy)
> @@ -1761,11 +1761,13 @@ final (rtx first, FILE *file, int optimi
>        start_to_bb = XCNEWVEC (basic_block, bb_map_size);
>        end_to_bb = XCNEWVEC (basic_block, bb_map_size);
>
> -      FOR_EACH_BB_REVERSE (bb)
> -       {
> -         start_to_bb[INSN_UID (BB_HEAD (bb))] = bb;
> -         end_to_bb[INSN_UID (BB_END (bb))] = bb;
> -       }
> +      /* There is no cfg for a thunk.  */
> +      if (!cfun->is_thunk)
> +       FOR_EACH_BB_REVERSE (bb)
> +         {
> +           start_to_bb[INSN_UID (BB_HEAD (bb))] = bb;
> +           end_to_bb[INSN_UID (BB_END (bb))] = bb;
> +         }
>      }
>
>    /* Output the insns.  */
> Index: gcc/cgraphunit.c
> ===================================================================
> --- gcc/cgraphunit.c    (revision 190189)
> +++ gcc/cgraphunit.c    (working copy)
> @@ -1799,6 +1799,10 @@ assemble_thunk (struct cgraph_node *node
>        init_function_start (thunk_fndecl);
>        cfun->is_thunk = 1;
>        assemble_start_function (thunk_fndecl, fnname);
> +      (*debug_hooks->source_line) (DECL_SOURCE_LINE (thunk_fndecl),
> +                                  DECL_SOURCE_FILE (thunk_fndecl),
> +                                  /* discriminator */ 0,
> +                                  /* is_stmt */ 1);
>
>        targetm.asm_out.output_mi_thunk (asm_out_file, thunk_fndecl,
>                                        fixed_offset, virtual_value, alias);
> Index: gcc/testsuite/g++.dg/debug/dwarf2/non-virtual-thunk.C
> ===================================================================
> --- gcc/testsuite/g++.dg/debug/dwarf2/non-virtual-thunk.C       (revision 0)
> +++ gcc/testsuite/g++.dg/debug/dwarf2/non-virtual-thunk.C       (revision 0)
> @@ -0,0 +1,39 @@
> +// { dg-do compile }
> +// { dg-options "-g2 -dA" }
> +
> +// Verify that line number info is output for the non-virtual
> +// thunks for C::~C().
> +// { dg-final { scan-assembler "thunk.C:30" } }
> +
> +class A
> +{
> + public:
> +  A();
> +  virtual ~A();
> + private:
> +  int i;
> +};
> +
> +class B
> +{
> + public:
> +  B();
> +  virtual ~B();
> + private:
> +  int i;
> +};
> +
> +class C : public A, public B
> +{
> + public:
> +  C();
> +  virtual ~C(); // line 30
> +};
> +
> +C::C()
> +{
> +}
> +
> +C::~C()
> +{
> +}