From 2c8361bd39f98c869df7b23ee682c25a9929f64f Mon Sep 17 00:00:00 2001
From: LemonBoy <LemonBoy@users.noreply.github.com>
Date: Fri, 31 Aug 2018 13:45:42 +0200
Subject: [PATCH] Constant folding for integer casts (#8095)

---
 compiler/semfold.nim                   | 32 +++++++++++---
 lib/posix/posix_linux_amd64_consts.nim |  2 +-
 tests/arithm/tcast.nim                 | 60 ++++++++++++++++++++++++++
 3 files changed, 86 insertions(+), 8 deletions(-)
 create mode 100644 tests/arithm/tcast.nim

diff --git a/compiler/semfold.nim b/compiler/semfold.nim
index 444940144..fe1871881 100644
--- a/compiler/semfold.nim
+++ b/compiler/semfold.nim
@@ -450,21 +450,38 @@ proc rangeCheck(n: PNode, value: BiggestInt; g: ModuleGraph) =
     localError(g.config, n.info, "cannot convert " & $value &
                                      " to " & typeToString(n.typ))
 
-proc foldConv*(n, a: PNode; g: ModuleGraph; check = false): PNode =
+proc foldConv(n, a: PNode; g: ModuleGraph; check = false): PNode =
+  let dstTyp = skipTypes(n.typ, abstractRange)
+  let srcTyp = skipTypes(a.typ, abstractRange)
+
   # XXX range checks?
-  case skipTypes(n.typ, abstractRange).kind
-  of tyInt..tyInt64, tyUInt..tyUInt64:
-    case skipTypes(a.typ, abstractRange).kind
+  case dstTyp.kind
+  of tyInt..tyInt64, tyUint..tyUInt64:
+    case srcTyp.kind
     of tyFloat..tyFloat64:
       result = newIntNodeT(int(getFloat(a)), n, g)
-    of tyChar: result = newIntNodeT(getOrdValue(a), n, g)
+    of tyChar:
+      result = newIntNodeT(getOrdValue(a), n, g)
+    of tyUInt8..tyUInt32, tyInt8..tyInt32:
+      let fromSigned = srcTyp.kind in tyInt..tyInt64
+      let toSigned = dstTyp.kind in tyInt..tyInt64
+
+      let mask = lastOrd(g.config, dstTyp, fixedUnsigned=true)
+
+      var val =
+        if toSigned:
+          a.getOrdValue mod mask
+        else:
+          a.getOrdValue and mask
+
+      result = newIntNodeT(val, n, g)
     else:
       result = a
       result.typ = n.typ
     if check and result.kind in {nkCharLit..nkUInt64Lit}:
       rangeCheck(n, result.intVal, g)
   of tyFloat..tyFloat64:
-    case skipTypes(a.typ, abstractRange).kind
+    case srcTyp.kind
     of tyInt..tyInt64, tyEnum, tyBool, tyChar:
       result = newFloatNodeT(toBiggestFloat(getOrdValue(a)), n, g)
     else:
@@ -742,7 +759,8 @@ proc getConstExpr(m: PSym, n: PNode; g: ModuleGraph): PNode =
   of nkHiddenStdConv, nkHiddenSubConv, nkConv:
     var a = getConstExpr(m, n.sons[1], g)
     if a == nil: return
-    result = foldConv(n, a, g, check=n.kind == nkHiddenStdConv)
+    # XXX: we should enable `check` for other conversion types too
+    result = foldConv(n, a, g, check=n.kind == nkHiddenSubConv)
   of nkCast:
     var a = getConstExpr(m, n.sons[1], g)
     if a == nil: return
diff --git a/lib/posix/posix_linux_amd64_consts.nim b/lib/posix/posix_linux_amd64_consts.nim
index ee4fac1e8..50b227635 100644
--- a/lib/posix/posix_linux_amd64_consts.nim
+++ b/lib/posix/posix_linux_amd64_consts.nim
@@ -300,7 +300,7 @@ const IPPROTO_TCP* = cint(6)
 const IPPROTO_UDP* = cint(17)
 const INADDR_ANY* = InAddrScalar(0)
 const INADDR_LOOPBACK* = InAddrScalar(2130706433)
-const INADDR_BROADCAST* = InAddrScalar(-1)
+const INADDR_BROADCAST* = InAddrScalar(4294967295)
 const INET_ADDRSTRLEN* = cint(16)
 const INET6_ADDRSTRLEN* = cint(46)
 const IPV6_JOIN_GROUP* = cint(20)
diff --git a/tests/arithm/tcast.nim b/tests/arithm/tcast.nim
new file mode 100644
index 000000000..954e2e677
--- /dev/null
+++ b/tests/arithm/tcast.nim
@@ -0,0 +1,60 @@
+discard """
+  output: '''
+B0
+B1
+B2
+B3
+'''
+"""
+
+template crossCheck(ty: untyped, exp: untyped) =
+  let rt = ty(exp)
+  const ct = ty(exp)
+  if $rt != $ct:
+    echo "Got ", ct
+    echo "Expected ", rt
+
+block:
+  when true:
+    echo "B0"
+    crossCheck(int8, 0'i16 - 5'i16)
+    crossCheck(int16, 0'i32 - 5'i32)
+    crossCheck(int32, 0'i64 - 5'i64)
+
+    echo "B1"
+    crossCheck(uint8, 0'u8 - 5'u8)
+    crossCheck(uint16, 0'u16 - 5'u16)
+    crossCheck(uint32, 0'u32 - 5'u32)
+    crossCheck(uint64, 0'u64 - 5'u64)
+
+    echo "B2"
+    crossCheck(uint8, uint8.high + 5'u8)
+    crossCheck(uint16, uint16.high + 5'u16)
+    crossCheck(uint32, uint32.high + 5'u32)
+    crossCheck(uint64, (-1).uint64 + 5'u64)
+
+    echo "B3"
+    crossCheck(int8, 0'u8 - 5'u8)
+    crossCheck(int16, 0'u16 - 5'u16)
+    crossCheck(int32, 0'u32 - 5'u32)
+    crossCheck(int64, 0'u64 - 5'u64)
+
+  # crossCheck(int8, 0'u16 - 129'u16)
+  # crossCheck(uint8, 0'i16 + 257'i16)
+
+  # Signed integer {under,over}flow is guarded against
+
+  # crossCheck(int8, int8.high + 5'i8)
+  # crossCheck(int16, int16.high + 5'i16)
+  # crossCheck(int32, int32.high + 5'i32)
+  # crossCheck(int64, int64.high + 5'i64)
+
+  # crossCheck(int8, int8.low - 5'i8)
+  # crossCheck(int16, int16.low - 5'i16)
+  # crossCheck(int32, int32.low - 5'i32)
+  # crossCheck(int64, int64.low - 5'i64)
+
+  # crossCheck(uint8, 0'i8 - 5'i8)
+  # crossCheck(uint16, 0'i16 - 5'i16)
+  # crossCheck(uint32, 0'i32 - 5'i32)
+  # crossCheck(uint64, 0'i64 - 5'i64)