[PATCH 07/15] rs6000: Generalize left shift in constant generation

[Richard Henderson]

Rather than always shift by 32, shift by the total number of zeros required.
The improvement to also look to shift out ones comes from Kenner via alpha.

Cc: David Edelsohn <dje....@gmail.com>
---
        * config/rs6000/rs6000.c (genimm_ppc::exam_search): Use ctz to
        compute the shift.  Also attempt to shift out ones.
---
 gcc/config/rs6000/rs6000.c | 21 +++++++++++++++++----
 1 file changed, 17 insertions(+), 4 deletions(-)

diff --git a/gcc/config/rs6000/rs6000.c b/gcc/config/rs6000/rs6000.c
index 59c5014..b27e476 100644
--- a/gcc/config/rs6000/rs6000.c
+++ b/gcc/config/rs6000/rs6000.c
@@ -8145,6 +8145,7 @@ genimm_ppc::exam_search (HOST_WIDE_INT c, int budget)
 {
   const int sub_budget = budget - 1;
   HOST_WIDE_INT test;
+  int bits;
 
   /* Simple arithmetic on the low 32-bits.  */
   test = c & 0xffff;
@@ -8181,11 +8182,23 @@ genimm_ppc::exam_search (HOST_WIDE_INT c, int budget)
     }
 
   /* Shift the constant left.  */
-  test = HOST_WIDE_INT_UC (0xffffffff00000000);
-  if ((c & test) == c && exam_sub (c >> 32, sub_budget))
+  bits = ctz_hwi (c);
+  if (bits > 0)
     {
-      opN (ASHIFT, 32); /* SLDI */
-      return true;
+      /* First try with zeros being shifted out.  */
+      HOST_WIDE_INT sub_c = (unsigned HOST_WIDE_INT)c >> bits;
+      bool ok = exam_sub (sub_c, sub_budget);
+      if (!ok)
+       {
+         /* If that failed, try with ones being shifted out.  */
+         sub_c |= ~(HOST_WIDE_INT_M1U >> bits);
+         ok = exam_sub (sub_c, sub_budget);
+       }
+      if (ok)
+       {
+         opN (ASHIFT, bits); /* SLDI */
+         return true;
+       }
     }
 
   return false;
-- 
2.4.3