[PATCH] Invalidate combiner's cached last value upon insn removal (PR rtl-optimization/79388, PR rtl-optimization/79450)

[Jakub Jelinek]

Hi!

On the following testcases combiner during notes distribution sees a
REG_DEAD note and decides to remove the setter thereof.  That register
has remembered a last value on that insn though, and it is a pseudo set
multiple times.  Later on we combine some further insns into
pseudo = pseudo op something and use the last known value of the pseudo at
the already deleted insn (0) and therefore simplify it into pseudo =
something.

Fixed thusly, bootstrapped/regtested on x86_64-linux and i686-linux, ok for
trunk?

2017-02-10  Jakub Jelinek  <ja...@redhat.com>

        PR rtl-optimization/79388
        PR rtl-optimization/79450
        * combine.c (distribute_notes): When removing TEM_INSN for which
        corresponding dest has last value recorded, invalidate that last
        value.

        * gcc.c-torture/execute/pr79388.c: New test.
        * gcc.c-torture/execute/pr79450.c: New test.

--- gcc/combine.c.jj    2017-01-30 09:31:48.000000000 +0100
+++ gcc/combine.c       2017-02-10 17:05:57.500482518 +0100
@@ -14288,6 +14288,11 @@ distribute_notes (rtx notes, rtx_insn *f
                                            NULL_RTX, NULL_RTX, NULL_RTX);
                          distribute_links (LOG_LINKS (tem_insn));
 
+                         unsigned int regno = REGNO (XEXP (note, 0));
+                         reg_stat_type *rsp = &reg_stat[regno];
+                         if (rsp->last_set == tem_insn)
+                           record_value_for_reg (XEXP (note, 0), NULL, 
NULL_RTX);
+
                          SET_INSN_DELETED (tem_insn);
                          if (tem_insn == i2)
                            i2 = NULL;
--- gcc/testsuite/gcc.c-torture/execute/pr79388.c.jj    2017-02-10 
17:03:01.993814529 +0100
+++ gcc/testsuite/gcc.c-torture/execute/pr79388.c       2017-02-10 
17:02:50.000000000 +0100
@@ -0,0 +1,23 @@
+/* PR rtl-optimization/79388 */
+/* { dg-additional-options "-fno-tree-coalesce-vars" } */
+
+unsigned int a, c;
+
+__attribute__ ((noinline, noclone)) unsigned int
+foo (unsigned int p)
+{
+  p |= 1;
+  p &= 0xfffe;
+  p %= 0xffff;
+  c = p;
+  return a + p;
+}
+
+int
+main (void)
+{
+  int x = foo (6);
+  if (x != 6)
+    __builtin_abort();
+  return 0;
+}
--- gcc/testsuite/gcc.c-torture/execute/pr79450.c.jj    2017-02-10 
17:03:45.698233423 +0100
+++ gcc/testsuite/gcc.c-torture/execute/pr79450.c       2017-02-10 
17:03:39.000000000 +0100
@@ -0,0 +1,22 @@
+/* PR rtl-optimization/79450 */
+
+unsigned int
+foo (unsigned char x, unsigned long long y)
+{
+  do
+    {
+      x &= !y;
+      x %= 24;
+    }
+  while (x < y);
+  return x + y;
+}
+
+int
+main (void)
+{
+  unsigned int x = foo (1, 0);
+  if (x != 1)
+    __builtin_abort ();
+  return 0;
+}

        Jakub