This patch fixes PR tree-optimization/102950, which is a P2 regression,
by providing better range bounds for BIT_XOR_EXPR, BIT_AND_EXPR and
BIT_IOR_EXPR on signed integer types. In general terms, any binary
bitwise operation on sign-extended or zero-extended integer types will
produce results that are themselves sign-extended or zero-extended.
More precisely, we can derive signed bounds from the number of leading
redundant sign bit copies, from the equation:
clrsb(X op Y) >= min (clrsb (X), clrsb(Y))
and from the property that for any (signed or unsigned) range [lb, ub]
that clrsb([lb, ub]) >= min (clrsb(lb), clrsb(ub)).
These can be used to show that [-1, 0] op [-1, 0] is [-1, 0] or that
[-128, 127] op [-128, 127] is [-128, 127], even when tracking nonzero
bits would result in VARYING (as every bit can be 0 or 1). This is
equivalent to determining the minimum type precision in which the
operation can be performed then sign extending the result.
One additional refinement is to observe that X ^ Y can never be
zero if the ranges of X and Y don't overlap, i.e. X can't be equal
to Y.
Previously, the expression "(int)(char)a ^ 233" in the PR was considered
VARYING, but with the above changes now has the range [-256, -1][1, 255],
which is sufficient to optimize away the call to foo.
This patch has been tested on x86_64-pc-linux-gnu with make bootstrap
and make -k check with no new failures. Ok for mainline?
2022-02-01 Roger Sayle <ro...@nextmovesoftware.com>
gcc/ChangeLog
PR tree-optimization/102950
* range-op.cc (wi_optimize_signed_bitwise_op): New function to
determine bounds of bitwise operations on signed types.
(operator_bitwise_and::wi_fold): Call the above function.
(operator_bitwise_or::wi_fold): Likewise.
(operator_bitwise_xor::wi_fold): Likewise. Additionally, the
result can't be zero if the operands can't be equal.
gcc/testsuite/ChangeLog
PR tree-optimization/102950
gcc.dg/pr102950.c: New test case.
gcc.dg/tree-ssa/evrp10.c: New test case.
Thanks in advance (and Happy Chinese New Year),
Roger
--
diff --git a/gcc/range-op.cc b/gcc/range-op.cc
index 19bdf30..71264ba 100644
--- a/gcc/range-op.cc
+++ b/gcc/range-op.cc
@@ -2659,6 +2659,29 @@ operator_bitwise_and::fold_range (irange &r, tree type,
}
+// Optimize BIT_AND_EXPR, BIT_IOR_EXPR and BIT_XOR_EXPR of signed types
+// by considering the number of leading redundant sign bit copies.
+// clrsb (X op Y) = min (clrsb (X), clrsb (Y)), so for example
+// [-1, 0] op [-1, 0] is [-1, 0] (where nonzero_bits doesn't help).
+static bool
+wi_optimize_signed_bitwise_op (irange &r, tree type,
+ const wide_int &lh_lb, const wide_int &lh_ub,
+ const wide_int &rh_lb, const wide_int &rh_ub)
+{
+ int lh_clrsb = MIN (wi::clrsb (lh_lb), wi::clrsb (lh_ub));
+ int rh_clrsb = MIN (wi::clrsb (rh_lb), wi::clrsb (rh_ub));
+ int new_clrsb = MIN (lh_clrsb, rh_clrsb);
+ if (new_clrsb == 0)
+ return false;
+ int type_prec = TYPE_PRECISION (type);
+ int rprec = (type_prec - new_clrsb) - 1;
+ value_range_with_overflow (r, type,
+ wi::mask (rprec, true, type_prec),
+ wi::mask (rprec, false, type_prec));
+ return true;
+}
+
+
// Optimize BIT_AND_EXPR and BIT_IOR_EXPR in terms of a mask if
// possible. Basically, see if we can optimize:
//
@@ -2839,7 +2862,14 @@ operator_bitwise_and::wi_fold (irange &r, tree type,
}
// If the limits got swapped around, return varying.
if (wi::gt_p (new_lb, new_ub,sign))
- r.set_varying (type);
+ {
+ if (sign == SIGNED
+ && wi_optimize_signed_bitwise_op (r, type,
+ lh_lb, lh_ub,
+ rh_lb, rh_ub))
+ return;
+ r.set_varying (type);
+ }
else
value_range_with_overflow (r, type, new_lb, new_ub);
}
@@ -3093,6 +3123,11 @@ operator_bitwise_or::wi_fold (irange &r, tree type,
|| wi::lt_p (lh_ub, 0, sign)
|| wi::lt_p (rh_ub, 0, sign))
r.set_nonzero (type);
+ else if (sign == SIGNED
+ && wi_optimize_signed_bitwise_op (r, type,
+ lh_lb, lh_ub,
+ rh_lb, rh_ub))
+ return;
else
r.set_varying (type);
return;
@@ -3180,8 +3215,23 @@ operator_bitwise_xor::wi_fold (irange &r, tree type,
// is better than VARYING.
if (wi::lt_p (new_lb, 0, sign) || wi::ge_p (new_ub, 0, sign))
value_range_with_overflow (r, type, new_lb, new_ub);
+ else if (sign == SIGNED
+ && wi_optimize_signed_bitwise_op (r, type,
+ lh_lb, lh_ub,
+ rh_lb, rh_ub))
+ ; /* Do nothing. */
else
r.set_varying (type);
+
+ /* Furthermore, XOR is non-zero if its arguments can't be equal. */
+ if (wi::lt_p (lh_ub, rh_lb, sign)
+ || wi::lt_p (rh_ub, lh_lb, sign)
+ || wi::ne_p (result_one_bits, 0))
+ {
+ int_range<2> tmp;
+ tmp.set_nonzero (type);
+ r.intersect (tmp);
+ }
}
bool
diff --git a/gcc/testsuite/gcc.dg/pr102950.c b/gcc/testsuite/gcc.dg/pr102950.c
new file mode 100644
index 0000000..0ab23bd
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/pr102950.c
@@ -0,0 +1,21 @@
+/* { dg-do link } */
+/* { dg-options "-O2" } */
+
+extern void link_error(void);
+
+static char a;
+static short d(unsigned e) {
+ char b;
+ short c;
+ a = b = e;
+ if (b)
+ return 0;
+ if (1 >= e) {
+ c = e == 0;
+ if (c)
+ link_error();
+ }
+ return 0;
+}
+int main() { d(a ^ 233); }
+
diff --git a/gcc/testsuite/gcc.dg/tree-ssa/evrp10.c
b/gcc/testsuite/gcc.dg/tree-ssa/evrp10.c
new file mode 100644
index 0000000..6ca00e4
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/tree-ssa/evrp10.c
@@ -0,0 +1,30 @@
+/* { dg-do compile } */
+/* { dg-options "-O2 -fdump-tree-evrp" }*/
+
+typedef __INT32_TYPE__ int32_t;
+
+int32_t and(int32_t x, int32_t y)
+{
+ int32_t tx = x >> 24;
+ int32_t ty = y >> 24;
+ int32_t t = tx & ty;
+ return t;
+}
+
+int32_t ior(int32_t x, int32_t y)
+{
+ int32_t tx = x >> 24;
+ int32_t ty = y >> 24;
+ int32_t t = tx | ty;
+ return t;
+}
+
+int32_t xor(int32_t x, int32_t y)
+{
+ int32_t tx = x >> 24;
+ int32_t ty = y >> 24;
+ int32_t t = tx ^ ty;
+ return t;
+}
+
+/* { dg-final { scan-tree-dump-times "\\\[-128, 127\\\]" 9 "evrp" } } */
