[PATCH] Don't DCE const/pure calls that can throw if cfg can't be altered (PR rtl-optimization/88870)

[Jakub Jelinek <jakub@redhat.com>]

Hi!

For normal instructions, deletable_insn_p has:
  /* Don't delete insns that may throw if we cannot do so.  */
  if (!(cfun->can_delete_dead_exceptions && can_alter_cfg)
      && !insn_nothrow_p (insn))
    return false;

The following patch adds that for the const/pure non-looping calls
that are handled earlier in the function as well (I haven't moved this test
earlier so we don't check insn_nothrow_p on jump insns etc.).

The other change is just to handle those calls the same as non-const/pure,
if we never consider them to be deletable, there is no point in
find_call_stack_args for them, like we don't do that for normal calls.

Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk?

2019-01-16  Jakub Jelinek  <jakub@redhat.com>

	PR rtl-optimization/88870
	* dce.c (deletable_insn_p): Never delete const/pure calls that can
	throw if we can't alter the cfg or delete dead exceptions.
	(mark_insn): Don't call find_call_stack_args for such calls.

	* gcc.dg/pr88870.c: New test.

--- gcc/dce.c.jj	2019-01-01 12:37:21.308906844 +0100
+++ gcc/dce.c	2019-01-16 11:39:13.432604633 +0100
@@ -108,7 +108,10 @@ deletable_insn_p (rtx_insn *insn, bool f
       /* We can delete dead const or pure calls as long as they do not
          infinite loop.  */
       && (RTL_CONST_OR_PURE_CALL_P (insn)
-	  && !RTL_LOOPING_CONST_OR_PURE_CALL_P (insn)))
+	  && !RTL_LOOPING_CONST_OR_PURE_CALL_P (insn))
+      /* Don't delete calls that may throw if we cannot do so.  */
+      && ((cfun->can_delete_dead_exceptions && can_alter_cfg)
+	  || insn_nothrow_p (insn)))
     return find_call_stack_args (as_a <rtx_call_insn *> (insn), false,
 				 fast, arg_stores);
 
@@ -201,7 +204,9 @@ mark_insn (rtx_insn *insn, bool fast)
 	  && !df_in_progress
 	  && !SIBLING_CALL_P (insn)
 	  && (RTL_CONST_OR_PURE_CALL_P (insn)
-	      && !RTL_LOOPING_CONST_OR_PURE_CALL_P (insn)))
+	      && !RTL_LOOPING_CONST_OR_PURE_CALL_P (insn))
+	  && ((cfun->can_delete_dead_exceptions && can_alter_cfg)
+	      || insn_nothrow_p (insn)))
 	find_call_stack_args (as_a <rtx_call_insn *> (insn), true, fast, NULL);
     }
 }
--- gcc/testsuite/gcc.dg/pr88870.c.jj	2019-01-16 11:25:01.434552788 +0100
+++ gcc/testsuite/gcc.dg/pr88870.c	2019-01-16 11:24:48.172769383 +0100
@@ -0,0 +1,23 @@
+/* PR rtl-optimization/88870 */
+/* { dg-do compile } */
+/* { dg-options "-O1 -fexceptions -fnon-call-exceptions -ftrapv -fno-tree-dominator-opts" } */
+
+int a, b;
+
+void
+foo (int *x)
+{
+  int c = 0;
+  {
+    int d;
+    x = &c;
+    for (;;)
+      {
+        x = &d;
+        b = 0;
+        d = c + 1;
+        b = c = 1;
+        ++a;
+      }
+  }
+}


	Jakub