[gcc r12-6403] middle-end/101530 - fix shufflevector lowering

[Richard Biener]

https://gcc.gnu.org/g:be59671c5624fe8bf21ddb0192e97ebdfa4db381

commit r12-6403-gbe59671c5624fe8bf21ddb0192e97ebdfa4db381
Author: Richard Biener <rguenther@suse.de>
Date:   Wed Jan 5 15:13:33 2022 +0100

    middle-end/101530 - fix shufflevector lowering
    
    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.
    
    FAIL: c-c++-common/torture/builtin-shufflevector-1.c   -O0  execution test
    
    2022-01-05  Richard Biener  <rguenther@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.

Diff:
---
 gcc/c-family/c-common.c                              |  7 +++++++
 gcc/testsuite/c-c++-common/builtin-shufflevector-3.c | 15 +++++++++++++++
 2 files changed, 22 insertions(+)

diff --git a/gcc/c-family/c-common.c b/gcc/c-family/c-common.c
index 13341fa315e..4a6a4edb763 100644
--- a/gcc/c-family/c-common.c
+++ b/gcc/c-family/c-common.c
@@ -1243,6 +1243,13 @@ 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);
+      DECL_CONTEXT (tem) = current_function_decl;
+      ret = build4 (TARGET_EXPR, lpartt, tem, ret, NULL_TREE, NULL_TREE);
+      TREE_SIDE_EFFECTS (ret) = 1;
     }
 
   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;
+}