[PATCH] middle-end/101530 - fix shufflevector lowering

[Richard Biener via Gcc-patches]

This makes __builtin_shufflevector lowering force the result
of the BIT_FIELD_REF lowpart operation to a temporary as to
fulfil the IL verifier constraint that BIT_FIELD_REFs should
be always in outermost handled component position.  Trying to
enforce this during gimplification isn't as straight-forward
as here where we know we're dealing with an rvalue.

Bootstrap & regtest running on x86_64-unknown-linux-gnu - OK for trunk?

Thanks,
Richard.

2022-01-05  Richard Biener  <rguent...@suse.de>

        PR middle-end/101530
gcc/c-family/
        * c-common.c (c_build_shufflevector): Wrap the BIT_FIELD_REF
        in a TARGET_EXPR to force a temporary.

gcc/testsuite/
        * c-c++-common/builtin-shufflevector-3.c: New testcase.
---
 gcc/c-family/c-common.c                           |  5 +++++
 .../c-c++-common/builtin-shufflevector-3.c        | 15 +++++++++++++++
 2 files changed, 20 insertions(+)
 create mode 100644 gcc/testsuite/c-c++-common/builtin-shufflevector-3.c

diff --git a/gcc/c-family/c-common.c b/gcc/c-family/c-common.c
index 13341fa315e..64209303d54 100644
--- a/gcc/c-family/c-common.c
+++ b/gcc/c-family/c-common.c
@@ -1243,6 +1243,11 @@ c_build_shufflevector (location_t loc, tree v0, tree v1,
       tree lpartt = build_vector_type (TREE_TYPE (ret_type), mask.length ());
       ret = build3_loc (loc, BIT_FIELD_REF,
                        lpartt, ret, TYPE_SIZE (lpartt), bitsize_zero_node);
+      /* Wrap the lowpart operation in a TARGET_EXPR so it gets a separate
+        temporary during gimplification.  See PR101530 for cases where
+        we'd otherwise end up with non-toplevel BIT_FIELD_REFs.  */
+      tree tem = create_tmp_var_raw (lpartt);
+      ret = build4 (TARGET_EXPR, lpartt, tem, ret, NULL_TREE, NULL_TREE);
     }
 
   if (!c_dialect_cxx () && !wrap)
diff --git a/gcc/testsuite/c-c++-common/builtin-shufflevector-3.c 
b/gcc/testsuite/c-c++-common/builtin-shufflevector-3.c
new file mode 100644
index 00000000000..0c9bda689ef
--- /dev/null
+++ b/gcc/testsuite/c-c++-common/builtin-shufflevector-3.c
@@ -0,0 +1,15 @@
+/* { dg-do compile } */
+
+typedef int __attribute__((__vector_size__ (sizeof(int)*4))) V;
+
+int
+foo(V v, int i)
+{
+  return __builtin_shufflevector (v, v, 2, 3)[i];
+}
+
+int
+bar(V v, int i)
+{
+  return __builtin_shufflevector(v, v, 4)[0] & i;
+}
-- 
2.31.1