[gcc r12-1724] Add relation between LHS and op1 for casts and copies.

[gcc r12-1724] Add relation between LHS and op1 for casts and copies.

[Andrew Macleod]

https://gcc.gnu.org/g:0f7ccc063a42407f91fa52a54cc480950a45e75c

commit r12-1724-g0f7ccc063a42407f91fa52a54cc480950a45e75c
Author: Andrew MacLeod <amacleod@redhat.com>
Date:   Thu Jun 17 13:39:02 2021 -0400

    Add relation between LHS and op1 for casts and copies.
    
            * range-op.cc (operator_cast::lhs_op1_relation): New.
            (operator_identity::lhs_op1_relation): Mew.

Diff:
---
 gcc/range-op.cc | 41 +++++++++++++++++++++++++++++++++++++++++
 1 file changed, 41 insertions(+)

diff --git a/gcc/range-op.cc b/gcc/range-op.cc
index ec4816d69fa..92b314df9dd 100644
--- a/gcc/range-op.cc
+++ b/gcc/range-op.cc
@@ -2115,6 +2115,10 @@ 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;
+
 private:
   bool truncating_cast_p (const irange &inner, const irange &outer) const;
   bool inside_domain_p (const wide_int &min, const wide_int &max,
@@ -2123,6 +2127,27 @@ private:
 			   const irange &outer) const;
 } op_convert;
 
+// Determine if there is a relationship between LHS and OP1.
+
+enum tree_code
+operator_cast::lhs_op1_relation (const irange &lhs,
+				 const irange &op1,
+				 const irange &op2 ATTRIBUTE_UNUSED) const
+{
+  if (op1.undefined_p ())
+    return VREL_NONE;
+  // We can't make larger types equivalent to smaller types because we can
+  // miss sign extensions in a chain of casts.
+  // u32 = 0xfffff
+  // s32 = (s32) u32
+  // s64 = (s64) s32
+  // we cant simply "convert" s64 = (s64)u32  or we get positive 0xffff
+  // value instead of sign extended negative value.
+  if (TYPE_PRECISION (lhs.type ()) == TYPE_PRECISION (op1.type ()))
+    return EQ_EXPR;
+  return VREL_NONE;
+}
+
 // Return TRUE if casting from INNER to OUTER is a truncating cast.
 
 inline bool
@@ -3325,8 +3350,24 @@ 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_identity;
 
+// Determine if there is a relationship between LHS and OP1.
+
+enum tree_code
+operator_identity::lhs_op1_relation (const irange &lhs,
+				     const irange &op1 ATTRIBUTE_UNUSED,
+				     const irange &op2 ATTRIBUTE_UNUSED) const
+{
+  if (lhs.undefined_p ())
+    return VREL_NONE;
+  // Simply a copy, so they are equivalent.
+  return EQ_EXPR;
+}
+
 bool
 operator_identity::fold_range (irange &r, tree type ATTRIBUTE_UNUSED,
 			       const irange &lh,