IR/VM: SGN sets status bits

docs/source/todo.rst

@@ -59,7 +59,8 @@ Future Things and Ideas
 
 IR/VM
 -----
-- make SGN set the N,Z flags and then optimize float<0 float==0 float>0 to use SGN instruction.  Check what code is generated for other data types.
+- optimize bool b = sgn(value)<0: still does a compare with 0 even though SGN sets all status bits. What is the code when a BIT instruction is used?
+- optimize float<0 float==0 float>0 to use SGN instruction?  Check what code is generated for other data types.
 - getting it in shape for code generation: the IR file should be able to encode every detail about a prog8 program (the VM doesn't have to actually be able to run all of it though!)
 - fix call() return value handling (... what's wrong with it again?)
 - proper code gen for the CALLI instruction and that it (optionally) returns a word value that needs to be assigned to a reg

examples/test.p8

@@ -31,10 +31,14 @@ main {
         txt.print_bool(b4)
         txt.nl()
 
-        b1 = sgn(bv)>0
-        b2 = sgn(wv)>0
-        b3 = sgn(lv)>0
-        b4 = sgn(fv)>0
+        bv = 1
+        wv = 1
+        lv = 1
+        fv = 1.1
+        b1 = sgn(bv)<0
+        b2 = sgn(wv)<0
+        b3 = sgn(lv)<0
+        b4 = sgn(fv)<0
         txt.print_bool(b1)
         txt.print_bool(b2)
         txt.print_bool(b3)

intermediate/src/prog8/intermediate/IRInstructions.kt

@@ -498,7 +498,8 @@ val OpcodesThatEndSSAblock = OpcodesThatBranchUnconditionally + arrayOf(
 val OpcodesThatSetStatusbitsIncludingCarry = arrayOf(
     Opcode.BIT,
     Opcode.CMP,
-    Opcode.CMPI
+    Opcode.CMPI,
+    Opcode.SGN
 )
 val OpcodesThatSetStatusbitsButNotCarry = arrayOf(
     Opcode.LOAD,

virtualmachine/src/prog8/vm/VirtualMachine.kt

@@ -1433,12 +1433,26 @@ class VirtualMachine(irProgram: IRProgram) {
     }
 
     private fun InsSGN(i: IRInstruction) {
+        var sign: Int
         when(i.type!!) {
-            IRDataType.BYTE -> registers.setSB(i.reg1!!, registers.getSB(i.reg2!!).toInt().sign.toByte())
-            IRDataType.WORD -> registers.setSB(i.reg1!!, registers.getSW(i.reg2!!).toInt().sign.toByte())
-            IRDataType.LONG -> registers.setSB(i.reg1!!, registers.getSL(i.reg2!!).sign.toByte())
-            IRDataType.FLOAT -> registers.setSB(i.reg1!!, registers.getFloat(i.fpReg1!!).sign.toInt().toByte())
+            IRDataType.BYTE -> {
+                sign = registers.getSB(i.reg2!!).toInt().sign
+                registers.setSB(i.reg1!!, sign.toByte())
+            }
+            IRDataType.WORD -> {
+                sign = registers.getSW(i.reg2!!).toInt().sign
+                registers.setSB(i.reg1!!, sign.toByte())
+            }
+            IRDataType.LONG -> {
+                sign = registers.getSL(i.reg2!!).sign
+                registers.setSB(i.reg1!!, sign.toByte())
+            }
+            IRDataType.FLOAT -> {
+                sign = registers.getFloat(i.fpReg1!!).sign.toInt()
+                registers.setSB(i.reg1!!, sign.toByte())
+            }
         }
+        statusbitsComparison(sign, i.type!!)
         nextPc()
     }