re PR tree-optimization/90883 (Generated code is worse if returned struct is unnamed)

	PR tree-optimization/90883
	* tree-ssa-alias.c (stmt_kills_ref_p): Handle BUILT_IN_CALLOC.
	* tree-ssa-dse.c: Update various comments to distinguish between
	dead and redundant stores.
	(initialize_ao_ref_for_dse): Handle BUILT_IN_CALLOC.
	(dse_optimize_redundant_stores): New function.
	(delete_dead_or_redundant_call): Renamed from delete_dead_call.
	Distinguish between dead and redundant calls in dump output.  All
	callers updated.
	(delete_dead_or_redundant_assignment): Similarly for assignments.
	(dse_optimize_stmt): Handle _CHK variants.  For statements which
	store 0 into multiple memory locations, try to prove a subsequent
	store is redundant.

        PR tree-optimization/90883
	* g++.dg/tree-ssa/pr90883.C: New test.
	* gcc.dg/tree-ssa/ssa-dse-36.c: New test.

From-SVN: r272717

1 files changed, 25 insertions, 2 deletions

diff --git a/gcc/tree-ssa-alias.c b/gcc/tree-ssa-alias.c
index 48f7364db2a..6e7db2b03a6 100644
--- a/gcc/tree-ssa-alias.c
+++ b/gcc/tree-ssa-alias.c
@@ -2849,13 +2849,36 @@ stmt_kills_ref_p (gimple *stmt, ao_ref *ref)
 	  case BUILT_IN_MEMSET_CHK:
 	  case BUILT_IN_STRNCPY:
 	  case BUILT_IN_STPNCPY:
+	  case BUILT_IN_CALLOC:
 	    {
 	      /* For a must-alias check we need to be able to constrain
 		 the access properly.  */
 	      if (!ref->max_size_known_p ())
 		return false;
-	      tree dest = gimple_call_arg (stmt, 0);
-	      tree len = gimple_call_arg (stmt, 2);
+	      tree dest;
+	      tree len;
+
+	      /* In execution order a calloc call will never kill
+		 anything.  However, DSE will (ab)use this interface
+		 to ask if a calloc call writes the same memory locations
+		 as a later assignment, memset, etc.  So handle calloc
+		 in the expected way.  */
+	      if (DECL_FUNCTION_CODE (callee) == BUILT_IN_CALLOC)
+		{
+		  tree arg0 = gimple_call_arg (stmt, 0);
+		  tree arg1 = gimple_call_arg (stmt, 1);
+		  if (TREE_CODE (arg0) != INTEGER_CST
+		      || TREE_CODE (arg1) != INTEGER_CST)
+		    return false;
+
+		  dest = gimple_call_lhs (stmt);
+		  len = fold_build2 (MULT_EXPR, TREE_TYPE (arg0), arg0, arg1);
+		}
+	      else
+		{
+		  dest = gimple_call_arg (stmt, 0);
+		  len = gimple_call_arg (stmt, 2);
+		}
 	      if (!poly_int_tree_p (len))
 		return false;
 	      tree rbase = ref->base;