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))
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