[Bug bootstrap/62077] --with-build-config=bootstrap-lto fails

["rguenth at gcc dot gnu.org" <gcc-bugzilla at gcc dot gnu dot org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=62077

--- Comment #23 from Richard Biener <rguenth at gcc dot gnu.org> ---
(In reply to Richard Biener from comment #22)
> So if I instrument build_string_literal with
> 
> Index: builtins.c
> ===================================================================
> --- builtins.c  (revision 213814)
> +++ builtins.c  (working copy)
> @@ -59,6 +59,8 @@ along with GCC; see the file COPYING3.
>  #include "builtins.h"
>  #include "ubsan.h"
>  #include "cilk.h"
> +#include "dumpfile.h"
> +#include "tree-pretty-print.h"
>  
>  
>  static tree do_mpc_arg1 (tree, tree, int (*)(mpc_ptr, mpc_srcptr,
> mpc_rnd_t));
> @@ -4695,6 +4697,15 @@ build_string_literal (int len, const cha
>    elem = build_type_variant (char_type_node, 1, 0);
>    index = build_index_type (size_int (len - 1));
>    type = build_array_type (elem, index);
> +  fprintf (stderr, "%s <%p> ", str, (void *)type);
> +  print_generic_expr (stderr, type, TDF_SLIM);
> +  if (TYPE_MAIN_VARIANT (type) == type)
> +    ;
> +  else
> +    {
> +      fprintf (stderr, " <%p> ", (void *)TYPE_MAIN_VARIANT (type));
> +      print_generic_expr (stderr, TYPE_MAIN_VARIANT (type), TDF_SLIM);
> +    }
> +  fprintf (stderr, "\n");
>    TREE_TYPE (t) = type;
>    TREE_CONSTANT (t) = 1;
>    TREE_READONLY (t) = 1;
> 
> 
> then I get for building non-LTO stage2 build/genconfig.o
> 
> #ifndef MAX_INSNS_PER_SPLIT
>  <0x7ffff5af4e70> const char[28]
> #endif
>  <0x7ffff5af6000> const char[7]
> #define HAVE_cc0 1
>  <0x7ffff5af6150> const char[19]
> #define CC0_P(X) ((X) == cc0_rtx)
>  <0x7ffff5af62a0> const char[34]
> #define CC0_P(X) ((X) ? 0 : 0)
>  <0x7ffff5aef540> const char[31] <0x7ffff5aef498> char[31]
> #define HAVE_conditional_move 1
>  <0x7ffff5aefe70> const char[32] <0x7ffff5de6d20> char[32]
> #define HAVE_conditional_execution 1
>  <0x7ffff5af6690> const char[37]
> #define HAVE_lo_sum 1
>  <0x7ffff5af67e0> const char[22]
> #define HAVE_peephole 1
>  <0x7ffff5af6930> const char[24]
> #define HAVE_peephole2 1
>  <0x7ffff5af45e8> const char[25] <0x7ffff5af4540> char[25]
> 
> and for stage3:
> 
> #ifndef MAX_INSNS_PER_SPLIT
>  <0x7ffff5db9150> const char[28]
> #endif
>  <0x7ffff601bc78> const char[7] <0x7ffff601bbd0> char[7]
> #define HAVE_cc0 1
>  <0x7ffff5db93f0> const char[19]
> #define CC0_P(X) ((X) == cc0_rtx)
>  <0x7ffff5db9540> const char[34]
> #define CC0_P(X) ((X) ? 0 : 0)
>  <0x7ffff5db17e0> const char[31] <0x7ffff5db1738> char[31]
> #define HAVE_conditional_move 1
>  <0x7ffff5db4150> const char[32] <0x7ffff6017888> char[32]
> #define HAVE_conditional_execution 1
>  <0x7ffff5db9930> const char[37]
> #define HAVE_lo_sum 1
>  <0x7ffff5db9a80> const char[22]
> #define HAVE_peephole 1
>  <0x7ffff5db9bd0> const char[24]
> #define HAVE_peephole2 1
>  <0x7ffff5db5888> const char[25] <0x7ffff5db57e0> char[25]
> 
> so whether the #endif literal has a TYPE_MAIN_VARIANT or not changes.
> Which means in one case somebody builds that very same array type
> earlier.
> 
> Instrumenting build_array_type I see that stage3 doesn't build some
> types stage2 builds.  Weird.
> 
> Ah.  Well - type_hash_table is marked as GC-able thus when using the
> stage1 compiler we run with --param ggc-min-expand=30 --param
> ggc-min-heapsize=4096 but when using the stage2 compiler we use
> --param ggc-min-expand=100 --param ggc-min-heapsize=131072.
> 
> using the same --param settings for stage2 fixes this difference
> (but not fully the miscompare in the LTO object).

Now a difference is only in .shstrtab (huh?).  Ah, from the differences
in section name due to hashing them (too lame reproducer).

So making GC behave the same for the stage1 compiler and the stage2
compiler fixes things.

trying

Index: config/bootstrap-lto.mk
===================================================================
--- config/bootstrap-lto.mk     (revision 213899)
+++ config/bootstrap-lto.mk     (working copy)
@@ -2,6 +2,6 @@
 # FIXME: Our build system is not yet able to use gcc-ar wrapper, so we need
 # to go with -ffat-lto-objects. 

-STAGE2_CFLAGS += -flto=jobserver -frandom-seed=1 -ffat-lto-objects
-STAGE3_CFLAGS += -flto=jobserver -frandom-seed=1 -ffat-lto-objects
+STAGE2_CFLAGS += -flto=jobserver -frandom-seed=1 -ffat-lto-objects --param
ggc-min-expand=100 --param ggc-min-heapsize=131072
+STAGE3_CFLAGS += -flto=jobserver -frandom-seed=1 -ffat-lto-objects --param
ggc-min-expand=100 --param ggc-min-heapsize=131072
 STAGEprofile_CFLAGS += -fno-lto