There are a limited number of existing rules that benefit from
knowing that a division is exact. Later patches will add more.
gcc/
* match.pd: Simplify X / (1 << C) to X /[ex] (1 << C) if the
low C bits of X are clear
gcc/testsuite/
* gcc.dg/tree-ssa/cmpexactdiv-6.c: New test.
---
gcc/match.pd | 9 ++++++
gcc/testsuite/gcc.dg/tree-ssa/cmpexactdiv-6.c | 29 +++++++++++++++++++
2 files changed, 38 insertions(+)
create mode 100644 gcc/testsuite/gcc.dg/tree-ssa/cmpexactdiv-6.c
diff --git a/gcc/match.pd b/gcc/match.pd
index 4aea028a866..b952225b08c 100644
--- a/gcc/match.pd
+++ b/gcc/match.pd
@@ -5431,6 +5431,15 @@ DEFINE_INT_AND_FLOAT_ROUND_FN (RINT)
TYPE_PRECISION (type)), 0))
(convert @0)))
+#if GIMPLE
+/* X / (1 << C) -> X /[ex] (1 << C) if the low C bits of X are clear. */
+(simplify
+ (trunc_div (with_possible_nonzero_bits2 @0) integer_pow2p@1)
+ (if (INTEGRAL_TYPE_P (type)
+ && !TYPE_UNSIGNED (type)
+ && wi::multiple_of_p (get_nonzero_bits (@0), wi::to_wide (@1), SIGNED))
+ (exact_div @0 @1)))
+#endif
/* (X /[ex] A) * A -> X. */
(simplify
diff --git a/gcc/testsuite/gcc.dg/tree-ssa/cmpexactdiv-6.c
b/gcc/testsuite/gcc.dg/tree-ssa/cmpexactdiv-6.c
new file mode 100644
index 00000000000..82d517b05ab
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/tree-ssa/cmpexactdiv-6.c
@@ -0,0 +1,29 @@
+/* { dg-options "-O2 -fdump-tree-optimized-raw" } */
+
+typedef __INTPTR_TYPE__ intptr_t;
+
+int
+f1 (int x, int y)
+{
+ if ((x & 1) || (y & 1))
+ __builtin_unreachable ();
+ x /= 2;
+ y /= 2;
+ return x < y;
+}
+
+int
+f2 (void *ptr1, void *ptr2, void *ptr3)
+{
+ ptr1 = __builtin_assume_aligned (ptr1, 4);
+ ptr2 = __builtin_assume_aligned (ptr2, 4);
+ ptr3 = __builtin_assume_aligned (ptr3, 4);
+ intptr_t diff1 = (intptr_t) ptr1 - (intptr_t) ptr2;
+ intptr_t diff2 = (intptr_t) ptr1 - (intptr_t) ptr3;
+ diff1 /= 2;
+ diff2 /= 2;
+ return diff1 < diff2;
+}
+
+/* { dg-final { scan-tree-dump-not {<[a-z]*_div_expr,} "optimized" } } */
+/* { dg-final { scan-tree-dump-not {<rshift_expr,} "optimized" } } */
--
2.25.1
