Fold (X<<C1)^(X<<C2) to a multiplication when possible.

The easiest way to motivate these additions to match.pd is with the
following example:

unsigned int foo(unsigned char i) {
  return i | (i<<8) | (i<<16) | (i<<24);
}

which mainline with -O2 on x86_64 currently generates:
foo:	movzbl  %dil, %edi
	movl    %edi, %eax
	movl    %edi, %edx
	sall    $8, %eax
	sall    $16, %edx
	orl     %edx, %eax
	orl     %edi, %eax
	sall    $24, %edi
	orl     %edi, %eax
	ret

but with this patch now becomes:
foo:	movzbl  %dil, %eax
        imull   $16843009, %eax, %eax
        ret

Interestingly, this transformation is already applied when using
addition, allowing synth_mult to select an optimal sequence, but
not when using the equivalent bit-wise ior or xor operators.

The solution is to use tree_nonzero_bits to check that the
potentially non-zero bits of each operand don't overlap, which
ensures that BIT_IOR_EXPR and BIT_XOR_EXPR produce the same
results as PLUS_EXPR, which effectively generalizes the old
fold_plusminus_mult_expr.  Technically, the transformation
is to canonicalize (X*C1)|(X*C2) and (X*C1)^(X*C2) to
X*(C1+C2) where X and X<<C are considered special cases.

2021-08-04  Roger Sayle  <roger@nextmovesoftware.com>
	    Marc Glisse  <marc.glisse@inria.fr>

gcc/ChangeLog
	* match.pd (bit_ior, bit_xor): Canonicalize (X*C1)|(X*C2) and
	(X*C1)^(X*C2) as X*(C1+C2), and related variants, using
	tree_nonzero_bits to ensure that operands are bit-wise disjoint.

gcc/testsuite/ChangeLog
	* gcc.dg/fold-ior-4.c: New test.

diff --git a/gcc/match.pd b/gcc/match.pd
index 19cbad7592787a568d4a7cfd62746d5844c0be5f..0fcfd0ea62c043dc217d0d560ce5b7e569b70e7d 100644 (file)
--- a/gcc/match.pd
+++ b/gcc/match.pd
@@ -2833,6 +2833,62 @@ DEFINE_INT_AND_FLOAT_ROUND_FN (RINT)
     (convert (mult (convert:t @0) { cst; })))))
 #endif
 
+/* Canonicalize (X*C1)|(X*C2) and (X*C1)^(X*C2) to (C1+C2)*X when
+   tree_nonzero_bits allows IOR and XOR to be treated like PLUS.
+   Likewise, handle (X<<C3) and X as legitimate variants of X*C.  */
+(for op (bit_ior bit_xor)
+ (simplify
+  (op (mult:s@0 @1 INTEGER_CST@2)
+      (mult:s@3 @1 INTEGER_CST@4))
+  (if (INTEGRAL_TYPE_P (type) && TYPE_OVERFLOW_WRAPS (type)
+       && (tree_nonzero_bits (@0) & tree_nonzero_bits (@3)) == 0)
+   (mult @1
+        { wide_int_to_tree (type, wi::to_wide (@2) + wi::to_wide (@4)); })))
+ (simplify
+  (op:c (mult:s@0 @1 INTEGER_CST@2)
+       (lshift:s@3 @1 INTEGER_CST@4))
+  (if (INTEGRAL_TYPE_P (type) && TYPE_OVERFLOW_WRAPS (type)
+       && tree_int_cst_sgn (@4) > 0
+       && (tree_nonzero_bits (@0) & tree_nonzero_bits (@3)) == 0)
+   (with { wide_int wone = wi::one (TYPE_PRECISION (type));
+          wide_int c = wi::add (wi::to_wide (@2),
+                                wi::lshift (wone, wi::to_wide (@4))); }
+    (mult @1 { wide_int_to_tree (type, c); }))))
+ (simplify
+  (op:c (mult:s@0 @1 INTEGER_CST@2)
+       @1)
+  (if (INTEGRAL_TYPE_P (type) && TYPE_OVERFLOW_WRAPS (type)
+       && (tree_nonzero_bits (@0) & tree_nonzero_bits (@1)) == 0)
+   (mult @1
+        { wide_int_to_tree (type,
+                            wi::add (wi::to_wide (@2), 1)); })))
+ (simplify
+  (op (lshift:s@0 @1 INTEGER_CST@2)
+      (lshift:s@3 @1 INTEGER_CST@4))
+  (if (INTEGRAL_TYPE_P (type)
+       && tree_int_cst_sgn (@2) > 0
+       && tree_int_cst_sgn (@4) > 0
+       && (tree_nonzero_bits (@0) & tree_nonzero_bits (@3)) == 0)
+   (with { tree t = type;
+          if (!TYPE_OVERFLOW_WRAPS (t))
+            t = unsigned_type_for (t);
+          wide_int wone = wi::one (TYPE_PRECISION (t));
+          wide_int c = wi::add (wi::lshift (wone, wi::to_wide (@2)),
+                                wi::lshift (wone, wi::to_wide (@4))); }
+    (convert (mult:t (convert:t @1) { wide_int_to_tree (t,c); })))))
+ (simplify
+  (op:c (lshift:s@0 @1 INTEGER_CST@2)
+       @1)
+  (if (INTEGRAL_TYPE_P (type)
+       && tree_int_cst_sgn (@2) > 0
+       && (tree_nonzero_bits (@0) & tree_nonzero_bits (@1)) == 0)
+   (with { tree t = type;
+          if (!TYPE_OVERFLOW_WRAPS (t))
+            t = unsigned_type_for (t);
+          wide_int wone = wi::one (TYPE_PRECISION (t));
+          wide_int c = wi::add (wi::lshift (wone, wi::to_wide (@2)), wone); }
+    (convert (mult:t (convert:t @1) { wide_int_to_tree (t, c); }))))))
+
 /* Simplifications of MIN_EXPR, MAX_EXPR, fmin() and fmax().  */
 
 (for minmax (min max FMIN_ALL FMAX_ALL)

diff --git a/gcc/testsuite/gcc.dg/fold-ior-4.c b/gcc/testsuite/gcc.dg/fold-ior-4.c
new file mode 100644 (file)
index 0000000..8f7213e
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/fold-ior-4.c
@@ -0,0 +1,61 @@
+/* { dg-do compile } */
+/* { dg-options "-O2 -fdump-tree-optimized" } */
+
+unsigned int test_ior(unsigned char i)
+{
+  return i | (i<<8) | (i<<16) | (i<<24);
+}
+
+unsigned int test_xor(unsigned char i)
+{
+  return i ^ (i<<8) ^ (i<<16) ^ (i<<24);
+}
+
+unsigned int test_ior_1s(unsigned char i)
+{
+  return i | (i<<8);
+}
+
+unsigned int test_ior_1u(unsigned char i)
+{
+  unsigned int t = i;
+  return t | (t<<8);
+}
+
+unsigned int test_xor_1s(unsigned char i)
+{
+  return i ^ (i<<8);
+}
+
+unsigned int test_xor_1u(unsigned char i)
+{
+  unsigned int t = i;
+  return t ^ (t<<8);
+}
+
+unsigned int test_ior_2s(unsigned char i)
+{
+  return (i<<8) | (i<<16);
+}
+
+unsigned int test_ior_2u(unsigned char i)
+{
+  unsigned int t = i;
+  return (t<<8) | (t<<16);
+}
+
+unsigned int test_xor_2s(unsigned char i)
+{
+  return (i<<8) ^ (i<<16);
+}
+
+unsigned int test_xor_2u(unsigned char i)
+{
+  unsigned int t = i;
+  return (t<<8) ^ (t<<16);
+}
+
+/* { dg-final { scan-tree-dump-not " \\^ " "optimized" } } */
+/* { dg-final { scan-tree-dump-not " \\| " "optimized" } } */
+/* { dg-final { scan-tree-dump-times " \\* 16843009" 2 "optimized" } } */
+