forwprop: Don't add uses to dce list if debug statement [PR116156]

The problem here is that when forwprop does a copy prop, into a statement,
we mark the uses of that statement as possibly need to be removed. But it just
happened that statement was a debug statement, there will be a difference when
compiling with debuging info turned on vs off; this is not expected.
So the fix is not to add the old use to dce list to process if it was a debug
statement.

Bootstrapped and tested on x86_64-linux-gnu with no regressions.

	PR tree-optimization/116156

gcc/ChangeLog:

	* tree-ssa-forwprop.cc (pass_forwprop::execute): Don't add
	uses if the statement was a debug statement.

gcc/testsuite/ChangeLog:

	* c-c++-common/torture/pr116156-1.c: New test.

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

2 files changed, 39 insertions, 7 deletions

diff --git a/gcc/testsuite/c-c++-common/torture/pr116156-1.c b/gcc/testsuite/c-c++-common/torture/pr116156-1.c
new file mode 100644
index 0000000..10f938e
--- /dev/null
+++ b/gcc/testsuite/c-c++-common/torture/pr116156-1.c
@@ -0,0 +1,30 @@
+/* { dg-additional-options "-fcompare-debug" } */
+/* PR tree-optimization/116156 */
+
+/* Forwprop used to delete an unused statement
+   but only with debug statements around. */
+
+struct jpeg_compress_struct {
+  int X_density;
+};
+void gg();
+int h(const char*,const char*) __attribute((pure));
+int h1(const char*) __attribute((pure));
+int f1() __attribute__((returns_twice));
+void real_save_jpeg(char **keys, char *values) {
+  struct jpeg_compress_struct cinfo;
+  int x_density = 0;
+  while (*keys)
+  {
+    if (h1(*keys) == 0)
+      gg();
+    if (h1(*keys) == 0)  {
+      if (!*values)
+        x_density = -1;
+      if (x_density <= 0)
+        gg();
+    }
+  }
+  if (f1())
+    cinfo.X_density = x_density;
+}
diff --git a/gcc/tree-ssa-forwprop.cc b/gcc/tree-ssa-forwprop.cc
index 44a6b5d..2e37642 100644
--- a/gcc/tree-ssa-forwprop.cc
+++ b/gcc/tree-ssa-forwprop.cc
@@ -3923,7 +3923,8 @@ pass_forwprop::execute (function *fun)
 	      tree val = fwprop_ssa_val (use);
 	      if (val && val != use)
 		{
-		  bitmap_set_bit (simple_dce_worklist, SSA_NAME_VERSION (use));
+		  if (!is_gimple_debug (stmt))
+		    bitmap_set_bit (simple_dce_worklist, SSA_NAME_VERSION (use));
 		  if (may_propagate_copy (use, val))
 		    {
 		      propagate_value (usep, val);
@@ -3963,12 +3964,13 @@ pass_forwprop::execute (function *fun)
 		    if (gimple_cond_true_p (cond)
 			|| gimple_cond_false_p (cond))
 		      cfg_changed = true;
-		  /* Queue old uses for simple DCE.  */
-		  for (tree use : uses)
-		    if (TREE_CODE (use) == SSA_NAME
-			&& !SSA_NAME_IS_DEFAULT_DEF (use))
-		      bitmap_set_bit (simple_dce_worklist,
-				      SSA_NAME_VERSION (use));
+		  /* Queue old uses for simple DCE if not debug statement.  */
+		  if (!is_gimple_debug (stmt))
+		    for (tree use : uses)
+		      if (TREE_CODE (use) == SSA_NAME
+			  && !SSA_NAME_IS_DEFAULT_DEF (use))
+			bitmap_set_bit (simple_dce_worklist,
+					SSA_NAME_VERSION (use));
 		}
 
 	      if (changed || substituted_p)