[Bug go/61265] New: gccgo: ICE in verify_gimple_in_seq [GoSmith]

[Bug go/61265] New: gccgo: ICE in verify_gimple_in_seq [GoSmith]

[dvyukov at google dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=61265

            Bug ID: 61265
           Summary: gccgo: ICE in verify_gimple_in_seq [GoSmith]
           Product: gcc
           Version: 4.10.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: go
          Assignee: ian at airs dot com
          Reporter: dvyukov at google dot com

Created attachment 32840
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=32840&action=edit
reproducer

gcc version 4.10.0 20140516 (experimental) (GCC)

The reproducer is attached (you need to set GOPATH to the root dir).

$ go build -compiler=gccgo main

# b
src/b/0.go: In function 'b.b..import':
src/b/0.go:1:1: error: non-trivial conversion at assignment
 package b
 ^
int16 *[1][0:18446744073709551615][0:18446744073709551615]
int16 *[1][1][1]
D.1019[0] = b.Var868;
src/b/0.go:1:1: internal compiler error: verify_gimple failed
0xa29b2f verify_gimple_in_seq(gimple_statement_base*)
    ../../gcc/tree-cfg.c:4622
0x83aae4 gimplify_body(tree_node*, bool)
    ../../gcc/gimplify.c:8720
0x83aee6 gimplify_function_tree(tree_node*)
    ../../gcc/gimplify.c:8805
0x5c552e Gcc_backend::write_global_definitions(std::vector<Btype*,
std::allocator<Btype*> > const&, std::vector<Bexpression*,
std::allocator<Bexpression*> > const&, std::vector<Bfunction*,
std::allocator<Bfunction*> > const&, std::vector<Bvariable*,
std::allocator<Bvariable*> > const&)
    ../../gcc/go/go-gcc.cc:2889
0x5e3592 Gogo::write_globals()
    ../../gcc/go/gofrontend/gogo.cc:1292

[Bug go/61265] gccgo: ICE in verify_gimple_in_seq [GoSmith]

[cmang at google dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=61265

--- Comment #2 from Chris Manghane <cmang at google dot com> ---
A slightly smaller program can reproduce this as well:

package main

var a = [1][0]int{B}[0]
var B = [0]int{}

func main() {}

This error occurs because in Gcc_backend::fill_in_array, the type of B, [0]int,
is represented using build_array_type(int, build_index_type(len - 1)), where
len is 0 in this case, giving it a range of [0:MAX_INT] where it should be
[0:0]. The following patch fixes this behavior:

Index: gcc/go/go-gcc.cc
======================================================================
--- a/gcc/go/go-gcc.cc
+++ b/gcc/go/go-gcc.cc
@@ -887,9 +887,13 @@ Gcc_backend::fill_in_array(Btype* fill, Btype*
element_type,

   // build_index_type takes the maximum index, which is one less than
   // the length.
-  tree index_type_tree = build_index_type(fold_build2(MINUS_EXPR, sizetype,
-                              length_tree,
-                              size_one_node));
+  tree index_type_tree = NULL_TREE;
+  if (length_tree == size_zero_node)
+    index_type_tree = build_index_type(size_zero_node);
+  else
+    index_type_tree = build_index_type(fold_build2(MINUS_EXPR, sizetype,
+                           length_tree,
+                           size_one_node));

   tree fill_tree = fill->get_tree();
   TREE_TYPE(fill_tree) = element_type_tree;

[Bug go/61265] gccgo: ICE in verify_gimple_in_seq [GoSmith]

[cmang at google dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=61265

--- Comment #3 from Chris Manghane <cmang at google dot com> ---
Sorry for the noise, responding with new information as I discover it.

The above patch doesn't really work (it fails a few tests) because this isn't a
problem with zero-sized array types, but rather a problem with zero-sized
elements in array types.

This same bug can be reproduced by

package main

var a = [1]struct{}{B}[0]
var B = struct{}{}

func main(){}

because struct{} is a zero-sized type and the backend implementation makes
assumptions about zero-sized globals for the linker. A better approach is to
just avoid constructing an array of zero-sized values and evaluate the
zero-valued expressions for their side effects. This is be done in
https://codereview.appspot.com/191970043/.

[Bug go/61265] gccgo: ICE in verify_gimple_in_seq [GoSmith]

[cmang at google dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=61265

Chris Manghane <cmang at google dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|ASSIGNED                    |RESOLVED
         Resolution|---                         |FIXED

--- Comment #4 from Chris Manghane <cmang at google dot com> ---
Fixed and test added to Go testsuite.