tree-ssa-dse.c (dse_optimize_redundant_stores): Improved check to catch more redundant zero initialization cases.

2019-08-19  Matthew Beliveau  <mbelivea@redhat.com>

	* tree-ssa-dse.c (dse_optimize_redundant_stores): Improved check to
	catch more redundant zero initialization cases.
	(dse_dom_walker::dse_optimize_stmt): Likewise.

From-SVN: r274749

5 files changed, 49 insertions, 15 deletions

diff --git a/gcc/ChangeLog b/gcc/ChangeLog
index 353429d..ecb7c065 100644
--- a/gcc/ChangeLog
+++ b/gcc/ChangeLog
@@ -1,3 +1,9 @@
+2019-08-20  Matthew Beliveau  <mbelivea@redhat.com>
+
+	* tree-ssa-dse.c (dse_optimize_redundant_stores): Improved check to
+	catch more redundant zero initialization cases.
+	(dse_dom_walker::dse_optimize_stmt): Likewise.
+
 2019-08-20  Richard Biener  <rguenther@suse.de>
 
 	PR lto/91307
diff --git a/gcc/testsuite/ChangeLog b/gcc/testsuite/ChangeLog
index 5316e07..0512a60 100644
--- a/gcc/testsuite/ChangeLog
+++ b/gcc/testsuite/ChangeLog
@@ -1,3 +1,8 @@
+2019-08-20  Matthew Beliveau  <mbelivea@redhat.com>
+
+	* gcc.dg/tree-ssa/redundant-assign-zero-1.c: New test.
+	* gcc.dg/tree-ssa/redundant-assign-zero-2.c: New test.
+
 2019-08-20  Richard Biener  <rguenther@suse.de>
 
 	PR tree-optimization/37242
diff --git a/gcc/testsuite/gcc.dg/tree-ssa/redundant-assign-zero-1.c b/gcc/testsuite/gcc.dg/tree-ssa/redundant-assign-zero-1.c
new file mode 100644
index 0000000..b8d01d1
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/tree-ssa/redundant-assign-zero-1.c
@@ -0,0 +1,13 @@
+/* { dg-do compile } */
+/* { dg-options "-O2 -fdump-tree-dse-details" } */
+
+void blah (char *);
+
+void bar ()
+{
+  char a[256] = "";
+  a[3] = 0; 
+  blah (a);
+}
+
+/* { dg-final { scan-tree-dump-times "Deleted redundant store" 1 "dse1"} } */
diff --git a/gcc/testsuite/gcc.dg/tree-ssa/redundant-assign-zero-2.c b/gcc/testsuite/gcc.dg/tree-ssa/redundant-assign-zero-2.c
new file mode 100644
index 0000000..8cefa6f
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/tree-ssa/redundant-assign-zero-2.c
@@ -0,0 +1,18 @@
+/* { dg-do compile } */
+/* { dg-options "-O2 -fdump-tree-dse-details" } */
+
+#include <string.h>
+
+void blahd (double *);
+
+void fubar ()
+{
+  double d;
+  double *x = &d;
+
+  memset (&d, 0 , sizeof d);
+  *x = 0.0;
+  blahd (x);
+}
+
+/* { dg-final { scan-tree-dump-times "Deleted redundant store" 1 "dse1"} } */
diff --git a/gcc/tree-ssa-dse.c b/gcc/tree-ssa-dse.c
index 5b7c4fc..ba67884 100644
--- a/gcc/tree-ssa-dse.c
+++ b/gcc/tree-ssa-dse.c
@@ -628,11 +628,8 @@ dse_optimize_redundant_stores (gimple *stmt)
       tree fndecl;
       if ((is_gimple_assign (use_stmt)
 	   && gimple_vdef (use_stmt)
-	   && ((gimple_assign_rhs_code (use_stmt) == CONSTRUCTOR
-	        && CONSTRUCTOR_NELTS (gimple_assign_rhs1 (use_stmt)) == 0
-	        && !gimple_clobber_p (stmt))
-	       || (gimple_assign_rhs_code (use_stmt) == INTEGER_CST
-		   && integer_zerop (gimple_assign_rhs1 (use_stmt)))))
+	   && (gimple_assign_single_p (use_stmt)
+	       && initializer_zerop (gimple_assign_rhs1 (use_stmt))))
 	  || (gimple_call_builtin_p (use_stmt, BUILT_IN_NORMAL)
 	      && (fndecl = gimple_call_fndecl (use_stmt)) != NULL
 	      && (DECL_FUNCTION_CODE (fndecl) == BUILT_IN_MEMSET
@@ -1027,16 +1024,11 @@ dse_dom_walker::dse_optimize_stmt (gimple_stmt_iterator *gsi)
     {
       bool by_clobber_p = false;
 
-      /* First see if this store is a CONSTRUCTOR and if there
-	 are subsequent CONSTRUCTOR stores which are totally
-	 subsumed by this statement.  If so remove the subsequent
-	 CONSTRUCTOR store.
-
-	 This will tend to make fewer calls into memset with longer
-	 arguments.  */
-      if (gimple_assign_rhs_code (stmt) == CONSTRUCTOR
-	  && CONSTRUCTOR_NELTS (gimple_assign_rhs1 (stmt)) == 0
-	  && !gimple_clobber_p (stmt))
+      /* Check if this statement stores zero to a memory location,
+	 and if there is a subsequent store of zero to the same
+	 memory location.  If so, remove the subsequent store.  */
+      if (gimple_assign_single_p (stmt)
+	  && initializer_zerop (gimple_assign_rhs1 (stmt)))
 	dse_optimize_redundant_stores (stmt);
 
       /* Self-assignments are zombies.  */