[PATCH] Fix PR71815 (SLSR misses PHI opportunities)

[Bill Schmidt]

Hi,

Here's version 2 of the patch to fix the missed SLSR PHI opportunities,
addressing Richard's comments.  I've repeated regstrap and SPEC testing
on powerpc64le-unknown-linux-gnu, again showing the patch as neutral
with respect to performance.  Is this ok for trunk?

Thanks for the review!

Bill


[gcc]

2016-06-23  Bill Schmidt  <wschmidt@linux.vnet.ibm.com>

	* gimple-ssa-strength-reduction.c (uses_consumed_by_stmt): New
	function.
	(find_basis_for_candidate): Call uses_consumed_by_stmt rather than
	has_single_use.
	(slsr_process_phi): Likewise.
	(replace_uncond_cands_and_profitable_phis): Don't replace a
	multiply candidate with a stride of 1 (copy or cast).
	(phi_incr_cost): Call uses_consumed_by_stmt rather than
	has_single_use.
	(lowest_cost_path): Likewise.
	(total_savings): Likewise.

[gcc/testsuite]

2016-06-23  Bill Schmidt  <wschmidt@linux.vnet.ibm.com>

	* gcc.dg/tree-ssa/slsr-35.c: Remove -fno-code-hoisting workaround.
	* gcc.dg/tree-ssa/slsr-36.c: Likewise.


Index: gcc/gimple-ssa-strength-reduction.c
===================================================================
--- gcc/gimple-ssa-strength-reduction.c	(revision 249223)
+++ gcc/gimple-ssa-strength-reduction.c	(working copy)
@@ -482,6 +482,36 @@ find_phi_def (tree base)
   return c->cand_num;
 }
 
+/* Determine whether all uses of NAME are directly or indirectly
+   used by STMT.  That is, we want to know whether if STMT goes
+   dead, the definition of NAME also goes dead.  */
+static bool
+uses_consumed_by_stmt (tree name, gimple *stmt, unsigned recurse = 0)
+{
+  gimple *use_stmt;
+  imm_use_iterator iter;
+  bool retval = true;
+
+  FOR_EACH_IMM_USE_STMT (use_stmt, iter, name)
+    {
+      if (use_stmt == stmt || is_gimple_debug (use_stmt))
+	continue;
+
+      if (!is_gimple_assign (use_stmt)
+	  || !gimple_get_lhs (use_stmt)
+	  || !is_gimple_reg (gimple_get_lhs (use_stmt))
+	  || recurse >= 10
+	  || !uses_consumed_by_stmt (gimple_get_lhs (use_stmt), stmt,
+				     recurse + 1))
+	{
+	  retval = false;
+	  BREAK_FROM_IMM_USE_STMT (iter);
+	}
+    }
+
+  return retval;
+}
+
 /* Helper routine for find_basis_for_candidate.  May be called twice:
    once for the candidate's base expr, and optionally again either for
    the candidate's phi definition or for a CAND_REF's alternative base
@@ -558,7 +588,8 @@ find_basis_for_candidate (slsr_cand_t c)
 
 	  /* If we found a hidden basis, estimate additional dead-code
 	     savings if the phi and its feeding statements can be removed.  */
-	  if (basis && has_single_use (gimple_phi_result (phi_cand->cand_stmt)))
+	  tree feeding_var = gimple_phi_result (phi_cand->cand_stmt);
+	  if (basis && uses_consumed_by_stmt (feeding_var, c->cand_stmt))
 	    c->dead_savings += phi_cand->dead_savings;
 	}
     }
@@ -789,7 +820,7 @@ slsr_process_phi (gphi *phi, bool speed)
 
 	  /* Gather potential dead code savings if the phi statement
 	     can be removed later on.  */
-	  if (has_single_use (arg))
+	  if (uses_consumed_by_stmt (arg, phi))
 	    {
 	      if (gimple_code (arg_stmt) == GIMPLE_PHI)
 		savings += arg_cand->dead_savings;
@@ -2479,7 +2510,9 @@ replace_uncond_cands_and_profitable_phis (slsr_can
 {
   if (phi_dependent_cand_p (c))
     {
-      if (c->kind == CAND_MULT)
+      /* A multiply candidate with a stride of 1 is just an artifice
+	 of a copy or cast; there is no value in replacing it.  */
+      if (c->kind == CAND_MULT && wi::to_widest (c->stride) != 1)
 	{
 	  /* A candidate dependent upon a phi will replace a multiply by 
 	     a constant with an add, and will insert at most one add for
@@ -2725,8 +2758,9 @@ phi_incr_cost (slsr_cand_t c, const widest_int &in
 	  if (gimple_code (arg_def) == GIMPLE_PHI)
 	    {
 	      int feeding_savings = 0;
+	      tree feeding_var = gimple_phi_result (arg_def);
 	      cost += phi_incr_cost (c, incr, arg_def, &feeding_savings);
-	      if (has_single_use (gimple_phi_result (arg_def)))
+	      if (uses_consumed_by_stmt (feeding_var, phi))
 		*savings += feeding_savings;
 	    }
 	  else
@@ -2739,7 +2773,7 @@ phi_incr_cost (slsr_cand_t c, const widest_int &in
 		  tree basis_lhs = gimple_assign_lhs (basis->cand_stmt);
 		  tree lhs = gimple_assign_lhs (arg_cand->cand_stmt);
 		  cost += add_cost (true, TYPE_MODE (TREE_TYPE (basis_lhs)));
-		  if (has_single_use (lhs))
+		  if (uses_consumed_by_stmt (lhs, phi))
 		    *savings += stmt_cost (arg_cand->cand_stmt, true);
 		}
 	    }
@@ -2816,7 +2850,7 @@ lowest_cost_path (int cost_in, int repl_savings, s
       gimple *phi = lookup_cand (c->def_phi)->cand_stmt;
       local_cost += phi_incr_cost (c, incr, phi, &savings);
 
-      if (has_single_use (gimple_phi_result (phi)))
+      if (uses_consumed_by_stmt (gimple_phi_result (phi), c->cand_stmt))
 	local_cost -= savings;
     }
 
@@ -2860,7 +2894,7 @@ total_savings (int repl_savings, slsr_cand_t c, co
       gimple *phi = lookup_cand (c->def_phi)->cand_stmt;
       savings -= phi_incr_cost (c, incr, phi, &phi_savings);
 
-      if (has_single_use (gimple_phi_result (phi)))
+      if (uses_consumed_by_stmt (gimple_phi_result (phi), c->cand_stmt))
 	savings += phi_savings;
     }
 
Index: gcc/testsuite/gcc.dg/tree-ssa/slsr-35.c
===================================================================
--- gcc/testsuite/gcc.dg/tree-ssa/slsr-35.c	(revision 249223)
+++ gcc/testsuite/gcc.dg/tree-ssa/slsr-35.c	(working copy)
@@ -3,7 +3,7 @@
    phi has an argument which is a parameter.  */
 
 /* { dg-do compile } */
-/* { dg-options "-O3 -fno-code-hoisting -fdump-tree-optimized" } */
+/* { dg-options "-O3 -fdump-tree-optimized" } */
 
 int
 f (int c, int i)
Index: gcc/testsuite/gcc.dg/tree-ssa/slsr-36.c
===================================================================
--- gcc/testsuite/gcc.dg/tree-ssa/slsr-36.c	(revision 249223)
+++ gcc/testsuite/gcc.dg/tree-ssa/slsr-36.c	(working copy)
@@ -3,7 +3,7 @@
    phi has an argument which is a parameter.  */
 
 /* { dg-do compile } */
-/* { dg-options "-O3 -fno-code-hoisting -fdump-tree-optimized" } */
+/* { dg-options "-O3 -fdump-tree-optimized" } */
 
 int
 f (int s, int c, int i)