DSE: Trim stores of 0 like triming stores of {} [PR87901]

This is the second part of the PR which comes from transformation
of memset into either stores of 0 (via an integral type) or stores
of {}. We already handle stores of `{}`, this just extends that to
handle of the constant 0 and treat it similarly.

	PR tree-optimization/87901

gcc/ChangeLog:

	* tree-ssa-dse.cc (maybe_trim_constructor_store): Add was_integer_cst argument.
	Check for was_integer_cst instead of `{}` when was_integer_cst is true.
	(maybe_trim_partially_dead_store): Handle INTEGER_CST stores of 0 as stores of `{}`.
	Udpate call to maybe_trim_constructor_store for CONSTRUCTOR.

gcc/testsuite/ChangeLog:

	* gcc.dg/tree-ssa/ssa-dse-53.c: New test.
	* gcc.dg/tree-ssa/ssa-dse-54.c: New test.

Signed-off-by: Andrew Pinski <quic_apinski@quicinc.com>

2 files changed, 51 insertions, 0 deletions

diff --git a/gcc/testsuite/gcc.dg/tree-ssa/ssa-dse-53.c b/gcc/testsuite/gcc.dg/tree-ssa/ssa-dse-53.c
new file mode 100644
index 0000000..a2df591
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/tree-ssa/ssa-dse-53.c
@@ -0,0 +1,26 @@
+/* { dg-options "-O2 -fno-strict-aliasing -fdump-tree-dse-details -fno-tree-fre -fdump-tree-optimized" } */
+
+/* PR tree-optimization/87901 */
+
+
+int i;
+int foo ()
+{
+  i = 0;
+  *((short *)&i + 1) = 1;
+  return i;
+}
+
+/* we should get:
+  MEM <char[2]> [(int *)&i] = {};
+  MEM[(short int *)&i + 2B] = 1;
+  in DSE1.
+
+  Note later on the stores will be merged.  */
+/* { dg-final { scan-tree-dump "return 65536;" "optimized" { target le } } } */
+/* { dg-final { scan-tree-dump "return 1;" "optimized" { target be } } } */
+/* { dg-final { scan-tree-dump "\\\[2\\\]" "dse1" } } */
+
+/* { dg-final { scan-tree-dump-times "Trimming statement " 1 "dse1" } } */
+
+
diff --git a/gcc/testsuite/gcc.dg/tree-ssa/ssa-dse-54.c b/gcc/testsuite/gcc.dg/tree-ssa/ssa-dse-54.c
new file mode 100644
index 0000000..7e79a73
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/tree-ssa/ssa-dse-54.c
@@ -0,0 +1,25 @@
+/* { dg-options "-O2 -fdump-tree-dse-details -fno-tree-fre -fdump-tree-optimized" } */
+
+/* PR tree-optimization/87901 */
+
+int z[128];
+void foo1(void)
+{
+  int z1;
+  int z2[24/sizeof(int)];
+  __builtin_memset (&z1, 0, sizeof(int));
+  __builtin_memcpy (z, &z1, sizeof(int));
+  __builtin_memset (z2, 0, 24);
+  __builtin_memcpy (((char*)z)+1, z2, 24);
+}
+
+/* we should get:
+  MEM[(char * {ref-all})&z] = {};
+  __builtin_memset (&MEM <int[128]> [(void *)&z + 1B], 0, 24);
+ */
+
+/* { dg-final { scan-tree-dump-not "MEM <unsigned int>" "optimized" } } */
+/* { dg-final { scan-tree-dump-not "MEM \\\[" "dse1" } } */
+/* { dg-final { scan-tree-dump-times "Trimming statement " 1 "dse1" } } */
+/* { dg-final { scan-tree-dump-times "Deleted dead call:" 1 "dse1" } } */
+