From: "Roger Sayle" <roger@nextmovesoftware.com>
To: <gcc-patches@gcc.gnu.org>
Subject: [PATCH] PR tree-optimization/71343: Optimize (X<<C)&(Y<<C) as (X&Y)<<C.
Date: Mon, 8 Aug 2022 09:07:16 +0100 [thread overview]
Message-ID: <00a501d8aafd$e10b6da0$a32248e0$@nextmovesoftware.com> (raw)
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This patch resolves PR tree-optimization/71343, a missed-optimization
enhancement request where GCC fails to see that (a<<2)+(b<<2) == a*4+b*4.
This requires two related (sets of) optimizations to be added to match.pd.
The first is that (X<<C) op (Y<<C) can be simplified to (X op Y) << C,
for many binary operators, including AND, IOR, XOR, and (if overflow
isn't an issue) PLUS and MINUS. Likewise, the right shifts (both logical
and arithmetic) and bit-wise logical operators can be simplified in a
similar fashion. These all reduce the number of GIMPLE binary operations
from 3 to 2, by combining/eliminating a shift operation.
The second optimization reflects that the middle-end doesn't impose a
canonical form on multiplications by powers of two, vs. left shifts,
instead leaving these operations as specified by the programmer
unless there's a good reason to change them. Hence, GIMPLE code may
contain the expressions "X * 8" and "X << 3" even though these represent
the same value/computation. The tweak to match.pd is that comparison
operations whose operands are equivalent non-canonical expressions can
be taught their equivalence. Hence "(X * 8) == (X << 3)" will always
evaluate to true, and "(X<<2) > 4*X" will always evaluate to false.
This patch has been tested on x86_64-pc-linux-gnu with make bootstrap
and make -k check, both with and without --target_board=unix{-m32},
with no new failures. Ok for mainline?
2022-08-08 Roger Sayle <roger@nextmovesoftware.com>
gcc/ChangeLog
PR tree-optimization/71343
* match.pd (op (lshift @0 @1) (lshift @2 @1)): Optimize the
expression (X<<C) + (Y<<C) to (X+Y)<<C for multiple operators.
(op (rshift @0 @1) (rshift @2 @1)): Likwise, simplify (X>>C)^(Y>>C)
to (X^Y)>>C for binary logical operators, AND, IOR and XOR.
(cmp:c (lshift @0) (mult @1)): Optimize comparisons between
shifts by integer constants and multiplications by powers of 2.
gcc/testsuite/ChangeLog
PR tree-optimization/71343
* gcc.dg/pr71343-1.c: New test case.
* gcc.dg/pr71343-2.c: Likewise.
Thanks in advance,
Roger
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diff --git a/gcc/match.pd b/gcc/match.pd
index f82f94a..d6b9cfb 100644
--- a/gcc/match.pd
+++ b/gcc/match.pd
@@ -982,6 +982,35 @@ DEFINE_INT_AND_FLOAT_ROUND_FN (RINT)
&& tree_nop_conversion_p (type, TREE_TYPE (@1)))
(lshift @0 @2)))
+/* Shifts by constants distribute over several binary operations,
+ hence (X << C) + (Y << C) can be simplified to (X + Y) << C. */
+(for op (plus minus)
+ (simplify
+ (op (lshift:s @0 INTEGER_CST@1) (lshift:s @2 INTEGER_CST@1))
+ (if (INTEGRAL_TYPE_P (type)
+ && TYPE_OVERFLOW_WRAPS (type)
+ && !TYPE_SATURATING (type)
+ && tree_fits_shwi_p (@1)
+ && tree_to_shwi (@1) > 0
+ && tree_to_shwi (@1) < TYPE_PRECISION (type))
+ (lshift (op @0 @2) @1))))
+
+(for op (bit_and bit_ior bit_xor)
+ (simplify
+ (op (lshift:s @0 INTEGER_CST@1) (lshift:s @2 INTEGER_CST@1))
+ (if (INTEGRAL_TYPE_P (type)
+ && tree_fits_shwi_p (@1)
+ && tree_to_shwi (@1) > 0
+ && tree_to_shwi (@1) < TYPE_PRECISION (type))
+ (lshift (op @0 @2) @1)))
+ (simplify
+ (op (rshift:s @0 INTEGER_CST@1) (rshift:s @2 INTEGER_CST@1))
+ (if (INTEGRAL_TYPE_P (type)
+ && tree_fits_shwi_p (@1)
+ && tree_to_shwi (@1) > 0
+ && tree_to_shwi (@1) < TYPE_PRECISION (type))
+ (rshift (op @0 @2) @1))))
+
/* Fold (1 << (C - x)) where C = precision(type) - 1
into ((1 << C) >> x). */
(simplify
@@ -2241,6 +2270,28 @@ DEFINE_INT_AND_FLOAT_ROUND_FN (RINT)
(if (TREE_INT_CST_LOW (@1) & 1)
{ constant_boolean_node (cmp == NE_EXPR, type); })))
+/* Some tree expressions are intentionally non-canonical.
+ We handle the comparison of the equivalent forms here. */
+(for cmp (eq le ge)
+ (simplify
+ (cmp:c (lshift @0 INTEGER_CST@1) (mult @0 integer_pow2p@2))
+ (if (INTEGRAL_TYPE_P (TREE_TYPE (@0))
+ && tree_fits_shwi_p (@1)
+ && tree_to_shwi (@1) > 0
+ && tree_to_shwi (@1) < TYPE_PRECISION (TREE_TYPE (@0))
+ && wi::to_wide (@1) == wi::exact_log2 (wi::to_wide (@2)))
+ { constant_boolean_node (true, type); })))
+
+(for cmp (ne lt gt)
+ (simplify
+ (cmp:c (lshift @0 INTEGER_CST@1) (mult @0 integer_pow2p@2))
+ (if (INTEGRAL_TYPE_P (TREE_TYPE (@0))
+ && tree_fits_shwi_p (@1)
+ && tree_to_shwi (@1) > 0
+ && tree_to_shwi (@1) < TYPE_PRECISION (TREE_TYPE (@0))
+ && wi::to_wide (@1) == wi::exact_log2 (wi::to_wide (@2)))
+ { constant_boolean_node (false, type); })))
+
/* Arguments on which one can call get_nonzero_bits to get the bits
possibly set. */
(match with_possible_nonzero_bits
diff --git a/gcc/testsuite/gcc.dg/pr71343-1.c b/gcc/testsuite/gcc.dg/pr71343-1.c
new file mode 100644
index 0000000..146f5fc
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/pr71343-1.c
@@ -0,0 +1,56 @@
+/* { dg-do compile } */
+/* { dg-options "-O2 -fdump-tree-optimized" } */
+
+unsigned int foo_plus(unsigned int a, unsigned int b)
+{
+ return (a << 2) + (b << 2);
+}
+
+unsigned int foo_and(unsigned int a, unsigned int b)
+{
+ return (a << 2) & (b << 2);
+}
+
+unsigned int foo_ior(unsigned int a, unsigned int b)
+{
+ return (a << 2) | (b << 2);
+}
+
+unsigned int foo_xor(unsigned int a, unsigned int b)
+{
+ return (a << 2) ^ (b << 2);
+}
+
+unsigned int bar_and(unsigned int a, unsigned int b)
+{
+ return (a >> 2) & (b >> 2);
+}
+
+unsigned int bar_ior(unsigned int a, unsigned int b)
+{
+ return (a >> 2) | (b >> 2);
+}
+
+unsigned int bar_xor(unsigned int a, unsigned int b)
+{
+ return (a >> 2) ^ (b >> 2);
+}
+
+int baz_and(int a, int b)
+{
+ return (a >> 2) & (b >> 2);
+}
+
+int baz_ior(int a, int b)
+{
+ return (a >> 2) | (b >> 2);
+}
+
+int baz_xor(int a, int b)
+{
+ return (a >> 2) ^ (b >> 2);
+}
+
+/* { dg-final { scan-tree-dump-times " << " 4 "optimized" } } */
+/* { dg-final { scan-tree-dump-times " >> " 6 "optimized" } } */
+
diff --git a/gcc/testsuite/gcc.dg/pr71343-2.c b/gcc/testsuite/gcc.dg/pr71343-2.c
new file mode 100644
index 0000000..11800a9
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/pr71343-2.c
@@ -0,0 +1,34 @@
+/* { dg-do compile } */
+/* { dg-options "-O2 -fdump-tree-optimized" } */
+
+unsigned int test1(unsigned int a , unsigned int b)
+{
+ return (a << 2) + (b << 2) == a * 4 + b * 4;
+}
+
+unsigned int test2(unsigned int a , unsigned int b)
+{
+ return (a << 2) + (b << 2) == (a + b) << 2;
+}
+
+unsigned int test3(unsigned int a , unsigned int b)
+{
+ return a * 4 + b * 4 == (a + b) * 4;
+}
+
+unsigned int test4(unsigned int a , unsigned int b)
+{
+ return (a + b) << 2 == (a + b) * 4;
+}
+
+unsigned int test5(unsigned int a , unsigned int b)
+{
+ return (a << 2) + (b << 2) == (a + b) * 4;
+}
+
+unsigned int test6(unsigned int a , unsigned int b)
+{
+ return (a + b) << 2 == a * 4 + b * 4;
+}
+
+/* { dg-final { scan-tree-dump-times "return 1" 6 "optimized" } } */
next reply other threads:[~2022-08-08 8:07 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-08-08 8:07 Roger Sayle [this message]
2022-08-08 11:42 ` Richard Biener
2022-08-12 21:45 ` [PATCH take #2] " Roger Sayle
2022-08-15 7:48 ` Richard Biener
2022-09-13 17:54 ` [PATCH] PR tree-optimization/71343: Value number X<<2 as X*4 Roger Sayle
2022-09-14 8:24 ` Richard Biener
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