backprop: Fix deleting of a phi node [PR116922]

The problem here is remove_unused_var is called on a name that is
defined by a phi node but it deletes it like removing a normal statement.
remove_phi_node should be called rather than gsi_remove for phinodes.

Note there is a possibility of using simple_dce_from_worklist instead
but that is for another day.

Bootstrapped and tested on x86_64-linux-gnu.

	PR tree-optimization/116922

gcc/ChangeLog:

	* gimple-ssa-backprop.cc (remove_unused_var): Handle phi
	nodes correctly.

gcc/testsuite/ChangeLog:

	* gcc.dg/torture/pr116922.c: New test.

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

2 files changed, 27 insertions, 2 deletions

diff --git a/gcc/gimple-ssa-backprop.cc b/gcc/gimple-ssa-backprop.cc
index fe27ef5..e3374b1 100644
--- a/gcc/gimple-ssa-backprop.cc
+++ b/gcc/gimple-ssa-backprop.cc
@@ -663,8 +663,14 @@ remove_unused_var (tree var)
       print_gimple_stmt (dump_file, stmt, 0, TDF_SLIM);
     }
   gimple_stmt_iterator gsi = gsi_for_stmt (stmt);
-  gsi_remove (&gsi, true);
-  release_defs (stmt);
+  if (gimple_code (stmt) == GIMPLE_PHI)
+    remove_phi_node (&gsi, true);
+  else
+    {
+      unlink_stmt_vdef (stmt);
+      gsi_remove (&gsi, true);
+      release_defs (stmt);
+    }
 }
 
 /* Note that we're replacing OLD_RHS with NEW_RHS in STMT.  */
diff --git a/gcc/testsuite/gcc.dg/torture/pr116922.c b/gcc/testsuite/gcc.dg/torture/pr116922.c
new file mode 100644
index 0000000..0fcf912
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/torture/pr116922.c
@@ -0,0 +1,19 @@
+/* { dg-do compile } */
+/* { dg-additional-options "-ffast-math" } */
+/* PR tree-optimization/116922 */
+
+
+static int g;
+
+void
+foo (int c, double v, double *r)
+{
+b:
+  do
+    v /= g - v;
+  while (c);
+  *r = v;
+
+  double x;
+  foo (5, (double)0, &x);
+}