[PATCH] Avoid extending lifetime of likely spilled hard regs in ifcvt before reload (PR rtl-optimization/56484)

[Jakub Jelinek]

Hi!

Without this patch, ifcvt extends lifetime of %eax hard register,
which causes reload/LRA ICE later on.  Combiner and other passes try hard
not to do that, even ifcvt has code for it if x is a hard register a few
lines below it, but in this case the hard register is SET_SRC (set_b).

With this patch we just use the pseudo (x) which has been initialized
from the hard register before the conditional.

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

2013-03-05  Jakub Jelinek  <ja...@redhat.com>

        PR rtl-optimization/56484
        * ifcvt.c (noce_process_if_block): Before reload if else_bb
        is NULL, avoid extending lifetimes of hard registers in
        likely to spilled or small register classes.

--- gcc/ifcvt.c.jj      2013-01-11 09:02:48.000000000 +0100
+++ gcc/ifcvt.c 2013-03-05 12:36:19.217251997 +0100
@@ -2491,6 +2491,15 @@ noce_process_if_block (struct noce_if_in
          || ! noce_operand_ok (SET_SRC (set_b))
          || reg_overlap_mentioned_p (x, SET_SRC (set_b))
          || modified_between_p (SET_SRC (set_b), insn_b, jump)
+         /* Avoid extending the lifetime of hard registers on small
+            register class machines before reload.  */
+         || (!reload_completed
+             && REG_P (SET_SRC (set_b))
+             && HARD_REGISTER_P (SET_SRC (set_b))
+             && (targetm.class_likely_spilled_p
+                   (REGNO_REG_CLASS (REGNO (SET_SRC (set_b))))
+                 || targetm.small_register_classes_for_mode_p
+                      (GET_MODE (SET_SRC (set_b)))))
          /* Likewise with X.  In particular this can happen when
             noce_get_condition looks farther back in the instruction
             stream than one might expect.  */
--- gcc/testsuite/gcc.c-torture/compile/pr56484.c.jj    2013-03-05 
12:42:24.972220034 +0100
+++ gcc/testsuite/gcc.c-torture/compile/pr56484.c       2013-03-05 
12:41:59.000000000 +0100
@@ -0,0 +1,17 @@
+/* PR rtl-optimization/56484 */
+
+unsigned char b[4096];
+int bar (void);
+
+int
+foo (void)
+{
+  int a = 0;
+  while (bar ())
+    {
+      int c = bar ();
+      a = a < 0 ? a : c;
+      __builtin_memset (b, 0, sizeof b);
+    }
+  return a;
+}

        Jakub