re PR tree-optimization/64705 (Bad code generation of sieve on x86-64 because of too aggressive IV optimizations)

	PR tree-optimization/64705
	* tree-ssa-loop-niter.h (expand_simple_operations): New parameter.
	* tree-ssa-loop-niter.c (expand_simple_operations): New parameter.
	* tree-ssa-loop-ivopts.c (extract_single_var_from_expr): New.
	(find_bivs, find_givs_in_stmt_scev): Pass new argument to
	expand_simple_operations.

	testsuite
	PR tree-optimization/64705
	* gcc.dg/tree-ssa/pr64705.c: New test.

From-SVN: r220676

1 files changed, 44 insertions, 5 deletions

diff --git a/gcc/tree-ssa-loop-ivopts.c b/gcc/tree-ssa-loop-ivopts.c
index 438ff96..6c96430 100644
--- a/gcc/tree-ssa-loop-ivopts.c
+++ b/gcc/tree-ssa-loop-ivopts.c
@@ -1081,13 +1081,40 @@ determine_biv_step (gphi *phi)
   return integer_zerop (iv.step) ? NULL_TREE : iv.step;
 }
 
+/* Return the first non-invariant ssa var found in EXPR.  */
+
+static tree
+extract_single_var_from_expr (tree expr)
+{
+  int i, n;
+  tree tmp;
+  enum tree_code code;
+
+  if (!expr || is_gimple_min_invariant (expr))
+    return NULL;
+
+  code = TREE_CODE (expr);
+  if (IS_EXPR_CODE_CLASS (TREE_CODE_CLASS (code)))
+    {
+      n = TREE_OPERAND_LENGTH (expr);
+      for (i = 0; i < n; i++)
+	{
+	  tmp = extract_single_var_from_expr (TREE_OPERAND (expr, i));
+
+	  if (tmp)
+	    return tmp;
+	}
+    }
+  return (TREE_CODE (expr) == SSA_NAME) ? expr : NULL;
+}
+
 /* Finds basic ivs.  */
 
 static bool
 find_bivs (struct ivopts_data *data)
 {
   gphi *phi;
-  tree step, type, base;
+  tree step, type, base, stop;
   bool found = false;
   struct loop *loop = data->current_loop;
   gphi_iterator psi;
@@ -1104,7 +1131,13 @@ find_bivs (struct ivopts_data *data)
 	continue;
 
       base = PHI_ARG_DEF_FROM_EDGE (phi, loop_preheader_edge (loop));
-      base = expand_simple_operations (base);
+      /* Stop expanding iv base at the first ssa var referred by iv step.
+	 Ideally we should stop at any ssa var, because that's expensive
+	 and unusual to happen, we just do it on the first one.
+
+	 See PR64705 for the rationale.  */
+      stop = extract_single_var_from_expr (step);
+      base = expand_simple_operations (base, stop);
       if (contains_abnormal_ssa_name_p (base)
 	  || contains_abnormal_ssa_name_p (step))
 	continue;
@@ -1176,7 +1209,7 @@ mark_bivs (struct ivopts_data *data)
 static bool
 find_givs_in_stmt_scev (struct ivopts_data *data, gimple stmt, affine_iv *iv)
 {
-  tree lhs;
+  tree lhs, stop;
   struct loop *loop = data->current_loop;
 
   iv->base = NULL_TREE;
@@ -1191,13 +1224,19 @@ find_givs_in_stmt_scev (struct ivopts_data *data, gimple stmt, affine_iv *iv)
 
   if (!simple_iv (loop, loop_containing_stmt (stmt), lhs, iv, true))
     return false;
-  iv->base = expand_simple_operations (iv->base);
 
+  /* Stop expanding iv base at the first ssa var referred by iv step.
+     Ideally we should stop at any ssa var, because that's expensive
+     and unusual to happen, we just do it on the first one.
+
+     See PR64705 for the rationale.  */
+  stop = extract_single_var_from_expr (iv->step);
+  iv->base = expand_simple_operations (iv->base, stop);
   if (contains_abnormal_ssa_name_p (iv->base)
       || contains_abnormal_ssa_name_p (iv->step))
     return false;
 
-  /* If STMT could throw, then do not consider STMT as defining a GIV.  
+  /* If STMT could throw, then do not consider STMT as defining a GIV.
      While this will suppress optimizations, we can not safely delete this
      GIV and associated statements, even if it appears it is not used.  */
   if (stmt_could_throw_p (stmt))