[PATCH][LRA] Fix PR88033: ICE in remove_some_program_points_and_update_live_ranges

[Peter Bergner]

PR88033 shows a problem when handling simple copies from a register to itself:

  (insn (set (reg:DI NNN) (reg:DI NNN)))

This was causing confusion in the code that performs liveness and conflict
updates and program point updates in lra-lives.c.  Trying to handle these
types of copies would add some ugly code.  It's easier to just bail on them
in non_conflicting_reg_copy_p() altogether, since by definition, a register
does not conflict with itself and so needs no special handling.  The patch
below implements that and fixes the ICE.

This is currently bootstrapping and regtesting on x86_64-linux.
Ok for mainline assuming the tests show no regressions?

Peter


gcc/
        PR rtl-optimization/88033
        * ira-lives.c (non_conflicting_reg_copy_p): Skip copies from a register
        to itself.  Use HARD_REGISTER_NUM_P.

gcc/testsuite/
        PR rtl-optimization/88033
        * gcc.target/i386/pr88033.c: New test.


Index: gcc/ira-lives.c
===================================================================
--- gcc/ira-lives.c     (revision 266207)
+++ gcc/ira-lives.c     (working copy)
@@ -1083,11 +1083,17 @@ non_conflicting_reg_copy_p (rtx_insn *insn)
   int src_regno = REGNO (SET_SRC (set));
   machine_mode mode = GET_MODE (SET_DEST (set));
 
+  /* By definition, a register does not conflict with itself, therefore we
+     do not have to handle it specially.  Returning NULL_RTX now, helps
+     simplify the callers of this function.  */
+  if (dst_regno == src_regno)
+    return NULL_RTX;
+
   /* Computing conflicts for register pairs is difficult to get right, so
      for now, disallow it.  */
-  if ((dst_regno < FIRST_PSEUDO_REGISTER
+  if ((HARD_REGISTER_NUM_P (dst_regno)
        && hard_regno_nregs (dst_regno, mode) != 1)
-      || (src_regno < FIRST_PSEUDO_REGISTER
+      || (HARD_REGISTER_NUM_P (src_regno)
          && hard_regno_nregs (src_regno, mode) != 1))
     return NULL_RTX;
 
Index: gcc/testsuite/gcc.target/i386/pr88033.c
===================================================================
--- gcc/testsuite/gcc.target/i386/pr88033.c     (nonexistent)
+++ gcc/testsuite/gcc.target/i386/pr88033.c     (working copy)
@@ -0,0 +1,14 @@
+/* { dg-do compile } */
+/* { dg-options "-O2" } */
+
+int
+main (long a, long *b, long c)
+{
+  if (!c)
+    return 0;
+  int g;
+  *b = (g & ~3000000000) < 0 ? a : a - g;
+  while (1)
+    ;
+  return 0;
+}