gnu: GCC: Fix union optimization issue.

* gnu/packages/patches/gcc-10-tree-sra-union-handling.patch: New file.
* gnu/local.mk (dist_patch_DATA): Adjust accordingly.
* gnu/packages/gcc.scm (gcc-10, gcc-11)[source](patches): Add it.
* gnu/packages/rust.scm (rust-bootstrap)[native-inputs]: Remove GCC-9.

1 files changed, 33 insertions, 0 deletions

diff --git a/gnu/packages/patches/gcc-10-tree-sra-union-handling.patch b/gnu/packages/patches/gcc-10-tree-sra-union-handling.patch
new file mode 100644
index 0000000000..aae5fc9f72
--- /dev/null
+++ b/gnu/packages/patches/gcc-10-tree-sra-union-handling.patch
@@ -0,0 +1,33 @@
+Fix a regression in GCC 10/11/12 where some union structures
+could get miscompiled when optimizations are enabled:
+
+  https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105860
+
+Taken from upstream:
+
+  https://gcc.gnu.org/g:16afe2e2862f3dd93c711d7f8d436dee23c6c34d
+
+diff --git a/gcc/tree-sra.c b/gcc/tree-sra.c
+index 09d951a261b..420329f63f6 100644
+--- a/gcc/tree-sra.c
++++ b/gcc/tree-sra.c
+@@ -1647,7 +1647,18 @@ build_ref_for_offset (location_t loc, tree base, poly_int64 offset,
+ static tree
+ build_reconstructed_reference (location_t, tree base, struct access *model)
+ {
+-  tree expr = model->expr, prev_expr = NULL;
++  tree expr = model->expr;
++  /* We have to make sure to start just below the outermost union.  */
++  tree start_expr = expr;
++  while (handled_component_p (expr))
++    {
++      if (TREE_CODE (TREE_TYPE (TREE_OPERAND (expr, 0))) == UNION_TYPE)
++	start_expr = expr;
++      expr = TREE_OPERAND (expr, 0);
++    }
++
++  expr = start_expr;
++  tree prev_expr = NULL_TREE;
+   while (!types_compatible_p (TREE_TYPE (expr), TREE_TYPE (base)))
+     {
+       if (!handled_component_p (expr))