middle-end/27800 - avoid unnecessary temporary during gimplification

This avoids a tempoary when gimplifying reg = a ? b : c, re-using
the LHS of an assignment if that's a register.

	PR middle-end/27800
	* gimplify.cc (gimplify_modify_expr_rhs): For a COND_EXPR
	avoid a temporary from gimplify_cond_expr when the LHS is
	a register by pushing the assignment into the COND_EXPR arms.

	* gcc.dg/pr27800.c: New testcase.

diff --git a/gcc/gimplify.cc b/gcc/gimplify.cc
index 7f94f5f50985b8dbade4e078c5243466907892ae..b0ed58ed0f917bf694b34d90c7f53f7196a8e791 100644 (file)
--- a/gcc/gimplify.cc
+++ b/gcc/gimplify.cc
@@ -6078,8 +6078,11 @@ gimplify_modify_expr_rhs (tree *expr_p, tree *from_p, tree *to_p,
          /* If we're assigning to a non-register type, push the assignment
             down into the branches.  This is mandatory for ADDRESSABLE types,
             since we cannot generate temporaries for such, but it saves a
-            copy in other cases as well.  */
-         if (!is_gimple_reg_type (TREE_TYPE (*from_p)))
+            copy in other cases as well.
+            Also avoid an extra temporary and copy when assigning to
+            a register.  */
+         if (!is_gimple_reg_type (TREE_TYPE (*from_p))
+             || (is_gimple_reg (*to_p) && !gimplify_ctxp->allow_rhs_cond_expr))
            {
              /* This code should mirror the code in gimplify_cond_expr. */
              enum tree_code code = TREE_CODE (*expr_p);

diff --git a/gcc/testsuite/gcc.dg/pr27800.c b/gcc/testsuite/gcc.dg/pr27800.c
new file mode 100644 (file)
index 0000000..e92ebc2
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/pr27800.c
@@ -0,0 +1,11 @@
+/* { dg-do compile } */
+/* { dg-options "-fdump-tree-gimple" } */
+
+int iii (int a, int b, int c)
+{
+  return a ? b : c;
+}
+
+/* Verify we end up with two assignments and not an extra copy
+   resulting from another temporary generated from gimplify_cond_expr.  */
+/* { dg-final { scan-tree-dump-times " = " 2 "gimple" } } */