opt: fold unary minus operations

This commit introduces a new rule, FoldUnaryMinus, which transforms
constant expressions of the form (UnaryMinus x) to -x.

There were some cases around this which would result in us not correctly
recognizing expressions like -1:::FLOAT as constant, causing us to
perform a full table scan instead of a point lookup.

Release note: None

pkg/sql/opt/exec/execbuilder/testdata/select

@@ -521,6 +521,45 @@ scan  ·       ·                          (f float)  ·
 statement ok
 DROP TABLE flt
 
+# ------------------------------------------------------------------------------
+# Verify we create the correct spans for negative numbers with extra
+# operations.
+# ------------------------------------------------------------------------------
+
+statement ok
+CREATE TABLE num (
+  i int null,
+  unique index (i),
+  f float null,
+  unique index (f),
+  d decimal null,
+  unique index (d)
+)
+
+query TTTTT
+EXPLAIN (TYPES) SELECT i FROM num WHERE i = -1:::INT
+----
+scan  ·      ·              (i int)  ·
+·     table  num@num_i_key  ·        ·
+·     spans  /-1-/0         ·        ·
+
+query TTTTT
+EXPLAIN (TYPES) SELECT f FROM num WHERE f = -1:::FLOAT
+----
+scan  ·      ·                  (f float)  ·
+·     table  num@num_f_key      ·          ·
+·     spans  /-1-/-1/PrefixEnd  ·          ·
+
+query TTTTT
+EXPLAIN (TYPES) SELECT d FROM num WHERE d = -1:::DECIMAL
+----
+scan  ·      ·                  (d decimal)  ·
+·     table  num@num_d_key      ·            ·
+·     spans  /-1-/-1/PrefixEnd  ·            ·
+
+statement ok
+DROP TABLE num
+
 # ------------------------------------------------------------------------------
 # ANY, ALL tests.
 # ------------------------------------------------------------------------------

pkg/sql/opt/idxconstraint/testdata/single-column

@@ -228,6 +228,16 @@ index-constraints vars=(int) index=(@1 desc)
 ----
 [/5 - /5]
 
+index-constraints vars=(int) index=(@1)
+@1 = -1
+----
+[/-1 - /-1]
+
+index-constraints vars=(decimal) index=(@1)
+@1 = -2.0
+----
+[/-2.0 - /-2.0]
+
 index-constraints vars=(int) index=(@1 desc)
 @1 IS DISTINCT FROM 5
 ----

pkg/sql/opt/norm/custom_funcs.go

@@ -761,3 +761,23 @@ func (c *CustomFuncs) IsOne(input memo.GroupID) bool {
 	}
 	return false
 }
+
+// NegateNumeric applies a unary minus to a numeric value.
+func (c *CustomFuncs) NegateNumeric(input memo.GroupID) memo.GroupID {
+	d := c.f.mem.LookupPrivate(c.f.mem.NormExpr(input).AsConst().Value()).(tree.Datum)
+	var id memo.PrivateID
+	switch t := d.(type) {
+	case *tree.DDecimal:
+		d := &tree.DDecimal{}
+		d.Decimal.Neg(&t.Decimal)
+		id = c.f.InternDatum(d)
+	case *tree.DFloat:
+		id = c.f.InternDatum(tree.NewDFloat(-*t))
+	case *tree.DInt:
+		id = c.f.InternDatum(tree.NewDInt(-*t))
+	default:
+		panic("unrecognized numeric type")
+	}
+
+	return c.f.ConstructConst(id)
+}

pkg/sql/opt/norm/rules/numeric.opt

@@ -65,3 +65,7 @@ $left
 # EliminateUnaryMinus discards a doubled UnaryMinus operator.
 [EliminateUnaryMinus, Normalize]
 (UnaryMinus (UnaryMinus $input:*)) => $input
+
+# FoldUnaryMinus negates a constant value within a UnaryMinus.
+[FoldUnaryMinus, Normalize]
+(UnaryMinus $input:(Const)) => (NegateNumeric $input)