[patch tree-ssa-math-opts]: Improve bswap detection

[Kai Tietz <ktietz@redhat.com>]

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Hello,

this patch improves the bswap (32/64) detection and fixes an issue about shifted bit values out of type-size precision.

ChangeLog

2011-06-27  Kai Tietz  <ktietz@redhat.com>

        * tree-ssa-math-opts.c (do_shift_rotate): Zero bits
        out of type precision after operation.
        (find_bswap): Take for limit value the integer auto-
        promotion into account.

ChangeLog

2011-06-27  Kai Tietz  <ktietz@redhat.com>

        * gcc.dg/optimize-bswapdi-2.c: New test.

Bootstrapped and regression tested for x86_64-pc-linux-gnu. Ok for apply?

Regards,
Kai

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Index: gcc-head/gcc/testsuite/gcc.dg/optimize-bswapdi-2.c
===================================================================
--- /dev/null
+++ gcc-head/gcc/testsuite/gcc.dg/optimize-bswapdi-2.c
@@ -0,0 +1,26 @@
+/* { dg-do compile { target arm*-*-* alpha*-*-* ia64*-*-* x86_64-*-* s390x-*-* powerpc*-*-* rs6000-*-* } } */
+/* { dg-require-effective-target stdint_types } */
+/* { dg-require-effective-target lp64 } */
+/* { dg-options "-O2 -fdump-tree-bswap" } */
+
+#include <stdint.h>
+
+/* A variant via unsigned short.  */
+
+uint64_t
+swap64_c (uint64_t x)
+{
+  uint16_t a0 = x >> 48;
+  uint16_t a1 = x >> 32;
+  uint16_t a2 = x >> 16;
+  uint16_t a3 = x;
+
+  return ((uint64_t) (((a0 >> 8) & 0xff) | ((a0 << 8) & 0xff00)))
+	| ((uint64_t) (((a1 >> 8) & 0xff) | ((a1 << 8) & 0xff00)) << 16)
+	| ((uint64_t) (((a2 >> 8) & 0xff) | ((a2 << 8) & 0xff00)) << 32)
+	| ((uint64_t) (((a3 >> 8) & 0xff) | ((a3 << 8) & 0xff00)) << 48);
+}
+
+
+/* { dg-final { scan-tree-dump-times "64 bit bswap implementation found at" 1 "bswap" } } */
+/* { dg-final { cleanup-tree-dump "bswap" } } */
Index: gcc-head/gcc/tree-ssa-math-opts.c
===================================================================
--- gcc-head.orig/gcc/tree-ssa-math-opts.c
+++ gcc-head/gcc/tree-ssa-math-opts.c
@@ -1543,6 +1543,9 @@ do_shift_rotate (enum tree_code code,
     default:
       return false;
     }
+  /* Zero unused bits for size.  */
+  if (n->size < (int)sizeof (HOST_WIDEST_INT))
+    n->n &= ((unsigned HOST_WIDEST_INT)1 << (n->size * BITS_PER_UNIT)) - 1;
   return true;
 }
 
@@ -1743,12 +1746,12 @@ find_bswap (gimple stmt)
 
   /* The last parameter determines the depth search limit.  It usually
      correlates directly to the number of bytes to be touched.  We
-     increase that number by one here in order to also cover signed ->
-     unsigned conversions of the src operand as can be seen in
-     libgcc.  */
+     increase that number by three  here in order to also
+     cover signed -> unsigned converions of the src operand as can be seen
+     in libgcc, and for initial shift/and operation of the src operand.  */
   source_expr =  find_bswap_1 (stmt, &n,
 			       TREE_INT_CST_LOW (
-				 TYPE_SIZE_UNIT (gimple_expr_type (stmt))) + 1);
+				 TYPE_SIZE_UNIT (gimple_expr_type (stmt))) + 3);
 
   if (!source_expr)
     return NULL_TREE;