Fold bswap32(x) != 0 to x != 0 (and related transforms)

This patch to match.pd implements several closely related folding
simplifications at the tree-level, that make use of the property
that bit permutation functions, rotate and bswap have inverses.

[1]	bswap(X) eq/ne C, for constant C, simplifies to X eq/ne C'
	where C'=bswap(C), generalizing the transform in the subject.
[2]	bswap(X) eq/ne bswap(Y) simplifies to X eq/ne Y.
[3]	lrotate(X,C1) eq/ne C2 simplifies to X eq/ne C3, where
	C3 = rrotate(C2,C1), i.e. apply the inverse rotation to C2.
[4]	Likewise, rrotate(X,C1) eq/ne C2 simplifies to X eq/ne C3,
	where C3 = lrotate(C2,C1).
[5]	rotate(X,Z) eq/ne rotate(Y,Z) simplifies to X eq/ne Y, when
	the bit-count Z (the same on both sides) has no side-effects.
[6]	rotate(X,Y) eq/ne 0 simplifies to X eq/ne 0 if Y has no
	side-effects.
[7]	Likewise, rotate(X,Y) eq/ne -1 simplifies to X eq/ne -1,
	if Y has no side-effects.

2010-07-26  Roger Sayle  <roger@nextmovesoftware.com>
	    Marc Glisse  <marc.glisse@inria.fr>

gcc/ChangeLog
	* match.pd (rotate): Simplify equality/inequality of rotations.
	(bswap): Simplify equality/inequality tests of byte swapping.

gcc/testsuite/ChangeLog
	* gcc.dg/fold-eqrotate-1.c: New test case.
	* gcc.dg/fold-eqbswap-1.c: New test case.

3 files changed, 183 insertions, 0 deletions

diff --git a/gcc/match.pd b/gcc/match.pd
index beb8d27..4d41b70 100644
--- a/gcc/match.pd
+++ b/gcc/match.pd
@@ -3312,6 +3312,23 @@ DEFINE_INT_AND_FLOAT_ROUND_FN (RINT)
      { tree rotate_type = TREE_TYPE (@0); }
       (convert (rotate (convert:rotate_type @1) @2))))))
 
+(for cmp (eq ne)
+ (for rotate (lrotate rrotate)
+      invrot (rrotate lrotate)
+  /* (X >>r Y) cmp (Z >>r Y) may simplify to X cmp Y. */
+  (simplify
+   (cmp (rotate @1 @0) (rotate @2 @0))
+   (cmp @1 @2))
+  /* (X >>r C1) cmp C2 may simplify to X cmp C3. */
+  (simplify
+   (cmp (rotate @0 INTEGER_CST@1) INTEGER_CST@2)
+   (cmp @0 { const_binop (invrot, TREE_TYPE (@0), @2, @1); }))
+  /* (X >>r Y) cmp C where C is 0 or ~0, may simplify to X cmp C.  */
+  (simplify
+   (cmp (rotate @0 @1) INTEGER_CST@2)
+    (if (integer_zerop (@2) || integer_all_onesp (@2))
+     (cmp @0 @2)))))
+
 /* Simplifications of conversions.  */
 
 /* Basic strip-useless-type-conversions / strip_nops.  */
@@ -3622,6 +3639,13 @@ DEFINE_INT_AND_FLOAT_ROUND_FN (RINT)
   (simplify
    (bswap (bitop:c (bswap @0) @1))
    (bitop @0 (bswap @1))))
+ (for cmp (eq ne)
+  (simplify
+   (cmp (bswap @0) (bswap @1))
+   (cmp @0 @1))
+  (simplify
+   (cmp (bswap @0) INTEGER_CST@1)
+   (cmp @0 (bswap @1))))
  /* (bswap(x) >> C1) & C2 can sometimes be simplified to (x >> C3) & C2.  */
  (simplify
   (bit_and (convert1? (rshift@0 (convert2? (bswap@4 @1)) INTEGER_CST@2))
diff --git a/gcc/testsuite/gcc.dg/fold-eqbswap-1.c b/gcc/testsuite/gcc.dg/fold-eqbswap-1.c
new file mode 100644
index 0000000..ed9820b
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/fold-eqbswap-1.c
@@ -0,0 +1,113 @@
+/* { dg-do compile } */
+/* { dg-options "-O2 -fdump-tree-optimized" } */
+
+int test1(int x, int y)
+{
+#if __SIZEOF_INT__ == 4
+  return __builtin_bswap32(x) == __builtin_bswap32(y);
+#else
+  return x == y;
+#endif
+}
+
+int test2(int x, int y)
+{
+#if __SIZEOF_INT__ == 4
+  return __builtin_bswap32(x) != __builtin_bswap32(y);
+#else
+  return x != y;
+#endif
+}
+
+int test3(int x)
+{
+#if __SIZEOF_INT__ == 4
+  return __builtin_bswap32(x) == 12345;
+#else
+  return x;
+#endif
+}
+
+int test4(int x)
+{
+#if __SIZEOF_INT__ == 4
+  return __builtin_bswap32(x) != 12345;
+#else
+  return x;
+#endif
+}
+
+int test1ll(long long x, long long y)
+{
+#if __SIZEOF_LONG_LONG__ == 8
+  return __builtin_bswap64(x) == __builtin_bswap64(y);
+#else
+  return x == y;
+#endif
+}
+
+int test2ll(long long x, long long y)
+{
+#if __SIZEOF_LONG_LONG__ == 8
+  return __builtin_bswap64(x) != __builtin_bswap64(y);
+#else
+  return x != y;
+#endif
+}
+
+int test3ll(long long x)
+{
+#if __SIZEOF_LONG_LONG__ == 8
+  return __builtin_bswap64(x) == 12345;
+#else
+  return (int)x;
+#endif
+}
+
+int test4ll(long long x)
+{
+#if __SIZEOF_LONG_LONG__ == 8
+  return __builtin_bswap64(x) != 12345;
+#else
+  return (int)x;
+#endif
+}
+
+int test1s(short x, short y)
+{
+#if __SIZEOF_SHORT__ == 2
+  return __builtin_bswap16(x) == __builtin_bswap16(y);
+#else
+  return x == y;
+#endif
+}
+
+int test2s(short x, short y)
+{
+#if __SIZEOF_SHORT__ == 2
+  return __builtin_bswap16(x) != __builtin_bswap16(y);
+#else
+  return x != y;
+#endif
+}
+
+int test3s(short x)
+{
+#if __SIZEOF_SHORT__ == 2
+  return __builtin_bswap16(x) == 12345;
+#else
+  return (int)x;
+#endif
+}
+
+int test4s(short x)
+{
+#if __SIZEOF_SHORT__ == 2
+  return __builtin_bswap16(x) != 12345;
+#else
+  return (int)x;
+#endif
+}
+
+/* { dg-final { scan-tree-dump-times "__builtin_bswap" 0 "optimized" } } */
+
diff --git a/gcc/testsuite/gcc.dg/fold-eqrotate-1.c b/gcc/testsuite/gcc.dg/fold-eqrotate-1.c
new file mode 100644
index 0000000..7d2b637
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/fold-eqrotate-1.c
@@ -0,0 +1,46 @@
+/* { dg-do compile } */
+/* { dg-options "-O2 -fdump-tree-optimized" } */
+
+int test1(unsigned int x, unsigned int y)
+{
+#if __SIZEOF_INT__ == 4
+  unsigned int r1 = (x << 16) | (x >> 16);
+  unsigned int r2 = (y << 16) | (y >> 16);
+  return r1 == r2;
+#else
+  return x == y;
+#endif
+}
+
+int test2(unsigned int x)
+{
+#if __SIZEOF_INT__ == 4
+  unsigned int r1 = (x << 16) | (x >> 16);
+  return r1 == 12345;
+#else
+  return x == 12345;
+#endif
+}
+
+int test3(unsigned int x)
+{
+#if __SIZEOF_INT__ == 4
+  unsigned int r1 = (x << 16) | (x >> 16);
+  return r1 == 0;
+#else
+  return x == 0;
+#endif
+}
+
+int test4(unsigned int x)
+{
+#if __SIZEOF_INT__ == 4
+  unsigned int r1 = (x << 16) | (x >> 16);
+  return r1 == ~0;
+#else
+  return x == ~0;
+#endif
+}
+
+/* { dg-final { scan-tree-dump-times "r>>" 0 "optimized" } } */
+