From: Eric Botcazou <ebotcazou@adacore.com>
Date: Wed, 11 Jan 2023 14:58:47 +0000 (+0100)
Subject: Fix problematic interaction between bitfields, unions, SSO and SRA
X-Git-Tag: release-12.2.mpacbti-rel1~153
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=eec3a65ed638a1c58fa08ddf508d2d60b64d311d;p=thirdparty%2Fgcc.git

Fix problematic interaction between bitfields, unions, SSO and SRA

The handling of bitfields by the SRA pass is peculiar and this must be taken
into account to support the scalar_storage_order attribute.

gcc/
	PR tree-optimization/108199
	* tree-sra.cc (sra_modify_expr): Deal with reverse storage order
	for bit-field references.

gcc/testsuite/
	* gcc.dg/sso-17.c: New test.
---

diff --git a/gcc/testsuite/gcc.dg/sso-17.c b/gcc/testsuite/gcc.dg/sso-17.c
new file mode 100644
index 000000000000..67e2d3793fde
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/sso-17.c
@@ -0,0 +1,52 @@
+/* { dg-do run } */
+/* { dg-options "-O2" } */
+
+#if __BYTE_ORDER__ == __ORDER_LITTLE_ENDIAN__
+#define REV_ENDIANNESS __attribute__((scalar_storage_order("big-endian")))
+#else
+#define REV_ENDIANNESS __attribute__((scalar_storage_order("little-endian")))
+#endif
+
+typedef unsigned long long u64;
+
+union DST {
+  u64 val;
+
+  struct {
+    u64 x : 1;
+    u64 y : 1;
+    u64 r: 62;
+  } REV_ENDIANNESS;
+} REV_ENDIANNESS;
+
+
+struct SRC {
+  u64 a;
+} REV_ENDIANNESS;
+
+[[gnu::noipa]]
+void foo () {__builtin_abort();}
+
+[[gnu::noinline]]
+int bar(struct SRC *src)
+{
+  union DST dst;
+  
+  dst.val = src->a;
+
+  if (dst.y) {
+    foo();
+  }
+  return 0;
+}
+
+int main(void)
+{
+#if __BYTE_ORDER__ == __ORDER_LITTLE_ENDIAN__
+  struct SRC t = {-1ull & (~(0x01ull<<62))};
+#else
+  struct SRC t = {-1ull & (~(0x01ull<<1))};
+#endif
+  bar(&t);
+  return 0;
+}
diff --git a/gcc/tree-sra.cc b/gcc/tree-sra.cc
index 95291e8df934..09dbd7be77fe 100644
--- a/gcc/tree-sra.cc
+++ b/gcc/tree-sra.cc
@@ -3858,7 +3858,23 @@ sra_modify_expr (tree *expr, gimple_stmt_iterator *gsi, bool write)
 	    }
 	}
       else
-	*expr = repl;
+	{
+	  /* If we are going to replace a scalar field in a structure with
+	     reverse storage order by a stand-alone scalar, we are going to
+	     effectively byte-swap the scalar and we also need to byte-swap
+	     the portion of it represented by the bit-field.  */
+	  if (bfr && REF_REVERSE_STORAGE_ORDER (bfr))
+	    {
+	      REF_REVERSE_STORAGE_ORDER (bfr) = 0;
+	      TREE_OPERAND (bfr, 2)
+		= size_binop (MINUS_EXPR, TYPE_SIZE (TREE_TYPE (repl)),
+			      size_binop (PLUS_EXPR, TREE_OPERAND (bfr, 1),
+						     TREE_OPERAND (bfr, 2)));
+	    }
+
+	  *expr = repl;
+	}
+
       sra_stats.exprs++;
     }
   else if (write && access->grp_to_be_debug_replaced)