tree-optimization/96707 - Add relation to unsigned right shift.

Message ID cb28bbf3-7f2c-2983-272d-39147aca865f@redhat.com
State New
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  • tree-optimization/96707 - Add relation to unsigned right shift.
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Commit Message

Patrick Palka via Gcc-patches Jan. 13, 2022, 1:57 p.m.
A quick addition to range ops for

LHS = OP1 >> OP2

if OP1 and OP2 are both >= 0,   then we can register the relation  LHS 
<= OP1   and all the expected good things happen.

Bootstrapped on x86_64-pc-linux-gnu with no regressions.

OK for trunk?

Andrew

Comments

Patrick Palka via Gcc-patches Jan. 13, 2022, 3:11 p.m. | #1
On Thu, Jan 13, 2022 at 2:58 PM Andrew MacLeod via Gcc-patches
<gcc-patches@gcc.gnu.org> wrote:
>

> A quick addition to range ops for

>

> LHS = OP1 >> OP2

>

> if OP1 and OP2 are both >= 0,   then we can register the relation  LHS

> <= OP1   and all the expected good things happen.

>

> Bootstrapped on x86_64-pc-linux-gnu with no regressions.

>

> OK for trunk?


OK.

>

> Andrew

Patch

From c34dab537d6f54b66b430f5980cde278fa033904 Mon Sep 17 00:00:00 2001
From: Andrew MacLeod <amacleod@redhat.com>
Date: Wed, 12 Jan 2022 13:28:55 -0500
Subject: [PATCH 1/2] Add relation to unsigned right shift.

If the first operand and the shift value of a right shift operation are both
>= 0, then we know the LHS of the operation is <= the first operand.

	PR tree-optimization/96707
	gcc/
	* range-op.c (operator_rshift::lhs_op1_relation): New.
	gcc/testtsuite/
	* g++.dg/pr96707.C: New.
---
 gcc/range-op.cc                | 16 ++++++++++++++++
 gcc/testsuite/g++.dg/pr96707.C | 10 ++++++++++
 2 files changed, 26 insertions(+)
 create mode 100644 gcc/testsuite/g++.dg/pr96707.C

diff --git a/gcc/range-op.cc b/gcc/range-op.cc
index a4f6e9eba29..19bdf30911a 100644
--- a/gcc/range-op.cc
+++ b/gcc/range-op.cc
@@ -1941,9 +1941,25 @@  public:
 			  const irange &lhs,
 			  const irange &op2,
 			  relation_kind rel = VREL_NONE) const;
+  virtual enum tree_code lhs_op1_relation (const irange &lhs,
+					   const irange &op1,
+					   const irange &op2) const;
 } op_rshift;
 
 
+enum tree_code
+operator_rshift::lhs_op1_relation (const irange &lhs ATTRIBUTE_UNUSED,
+				   const irange &op1,
+				   const irange &op2) const
+{
+  // If both operands range are >= 0, then the LHS <= op1.
+  if (!op1.undefined_p () && !op2.undefined_p ()
+      && wi::ge_p (op1.lower_bound (), 0, TYPE_SIGN (op1.type ()))
+      && wi::ge_p (op2.lower_bound (), 0, TYPE_SIGN (op2.type ())))
+    return LE_EXPR;
+  return VREL_NONE;
+}
+
 bool
 operator_lshift::fold_range (irange &r, tree type,
 			     const irange &op1,
diff --git a/gcc/testsuite/g++.dg/pr96707.C b/gcc/testsuite/g++.dg/pr96707.C
new file mode 100644
index 00000000000..2653fe3d043
--- /dev/null
+++ b/gcc/testsuite/g++.dg/pr96707.C
@@ -0,0 +1,10 @@ 
+/* { dg-do compile} */
+/* { dg-options "-O2 -fdump-tree-evrp" } */
+
+bool f(unsigned x, unsigned y)
+{
+    return (x >> y) <= x;
+}
+
+/* { dg-final { scan-tree-dump "return 1" "evrp" } }  */
+
-- 
2.17.2