vm/ir: for loop is now correctly skipped if loopvar>endvar

this is different still in the 6502 codegen, where it wraps around $00!

codeGenIntermediate/src/prog8/codegen/intermediate/IRCodeGen.kt

@@ -542,12 +542,19 @@ class IRCodeGen(
 
         result += expressionEval.translateExpression(iterable.to, endvalueReg, -1)
         result += expressionEval.translateExpression(iterable.from, indexReg, -1)
+
+        val labelAfterFor = createLabelName()
+        val greaterOpcode = if(loopvarDt in SignedDatatypes) Opcode.BGTS else Opcode.BGT
+        addInstr(result, IRInstruction(greaterOpcode, loopvarDtIr, indexReg, endvalueReg, labelSymbol=labelAfterFor), null)
+
         addInstr(result, IRInstruction(Opcode.STOREM, loopvarDtIr, reg1=indexReg, labelSymbol=loopvarSymbol), null)
         result += labelFirstChunk(translateNode(forLoop.statements), loopLabel)
         result += addConstMem(loopvarDtIr, null, loopvarSymbol, step)
         addInstr(result, IRInstruction(Opcode.LOADM, loopvarDtIr, reg1 = indexReg, labelSymbol = loopvarSymbol), null)
         val branchOpcode = if(loopvarDt in SignedDatatypes) Opcode.BLES else Opcode.BLE
         addInstr(result, IRInstruction(branchOpcode, loopvarDtIr, reg1=indexReg, reg2=endvalueReg, labelSymbol=loopLabel), null)
+
+        result += IRCodeChunk(labelAfterFor, null)
         return result
     }
 

compiler/res/version.txt

@@ -1 +1 @@
-8.8.1
+8.9-dev

docs/source/todo.rst

@@ -3,6 +3,7 @@ TODO
 
 For next release
 ^^^^^^^^^^^^^^^^
+- remove redundant branch opcodes in IR: BLT(S), BLE(S). Replace by swapped BGT(S), BGE(S).
 - make sure bool value is always 0 or 1 (all casts should convert), then:
     - rewrite bool=bool^1 into bool=not bool
     - should solve: bool bb = not bb -> larger code than bool bb ^= 1
@@ -33,10 +34,10 @@ Compiler:
 - ir peephole opt: reuse registers in chunks (but keep result registers in mind that pass values out!)
 - ir: add more optimizations in IRPeepholeOptimizer
 - vm: somehow be able to load a label address as value? (VmProgramLoader)
-- see if we can let for loops skip the loop if end<start, like other programming languages. Without adding a lot of code size/duplicating the loop condition.
+- 6502 codegen: see if we can let for loops skip the loop if startvar>endvar, without adding a lot of code size/duplicating the loop condition.
-  this is documented behavior to now loop around but it's too easy to forget about!
+  It is documented behavior to now loop 'around' $00 but it's too easy to forget about!
-  Lot of work because of so many special cases in ForLoopsAsmgen.....
+  Lot of work because of so many special cases in ForLoopsAsmgen.....  (vm codegen already behaves like this)
-  How is it for the vm target? -> just 2 special cases in CodeGen.
+- ir: can we determine for the loop variable in forloops if it could be kept in a (virtual) register instead of a real variable? Need to be able to check if the variable is used by another statement beside just the for loop.
 - createAssemblyAndAssemble(): make it possible to actually get rid of the VarDecl nodes by fixing the rest of the code mentioned there.
   but probably better to rewrite the 6502 codegen on top of the new Ast.
 - generate WASM to eventually run prog8 on a browser canvas?

intermediate/src/prog8/intermediate/IRInstructions.kt

@@ -76,20 +76,20 @@ bz          reg1,             address   - branch to location if reg1 is zero
 bnz         reg1,             address   - branch to location if reg1 is not zero
 beq         reg1, reg2,       address   - jump to location in program given by location, if reg1 == reg2
 bne         reg1, reg2,       address   - jump to location in program given by location, if reg1 != reg2
-blt         reg1, reg2,       address   - jump to location in program given by location, if reg1 < reg2 (unsigned)
+blt         reg1, reg2,       address   - jump to location in program given by location, if reg1 < reg2 (unsigned)    TODO REMOVE
-blts        reg1, reg2,       address   - jump to location in program given by location, if reg1 < reg2 (signed)
+blts        reg1, reg2,       address   - jump to location in program given by location, if reg1 < reg2 (signed)      TODO REMOVE
-ble         reg1, reg2,       address   - jump to location in program given by location, if reg1 <= reg2 (unsigned)
+ble         reg1, reg2,       address   - jump to location in program given by location, if reg1 <= reg2 (unsigned)   TODO REMOVE
-bles        reg1, reg2,       address   - jump to location in program given by location, if reg1 <= reg2 (signed)
+bles        reg1, reg2,       address   - jump to location in program given by location, if reg1 <= reg2 (signed)     TODO REMOVE
 bgt         reg1, reg2,       address   - jump to location in program given by location, if reg1 > reg2 (unsigned)
 bgts        reg1, reg2,       address   - jump to location in program given by location, if reg1 > reg2 (signed)
 bge         reg1, reg2,       address   - jump to location in program given by location, if reg1 >= reg2 (unsigned)
 bges        reg1, reg2,       address   - jump to location in program given by location, if reg1 >= reg2 (signed)
 seq         reg1, reg2                  - set reg=1 if reg1 == reg2,  otherwise set reg1=0
 sne         reg1, reg2                  - set reg=1 if reg1 != reg2,  otherwise set reg1=0
-slt         reg1, reg2                  - set reg=1 if reg1 < reg2 (unsigned),  otherwise set reg1=0
+slt         reg1, reg2                  - set reg=1 if reg1 < reg2 (unsigned),  otherwise set reg1=0        TODO REMOVE
-slts        reg1, reg2                  - set reg=1 if reg1 < reg2 (signed),  otherwise set reg1=0
+slts        reg1, reg2                  - set reg=1 if reg1 < reg2 (signed),  otherwise set reg1=0          TODO REMOVE
-sle         reg1, reg2                  - set reg=1 if reg1 <= reg2 (unsigned),  otherwise set reg1=0
+sle         reg1, reg2                  - set reg=1 if reg1 <= reg2 (unsigned),  otherwise set reg1=0       TODO REMOVE
-sles        reg1, reg2                  - set reg=1 if reg1 <= reg2 (signed),  otherwise set reg1=0
+sles        reg1, reg2                  - set reg=1 if reg1 <= reg2 (signed),  otherwise set reg1=0         TODO REMOVE
 sgt         reg1, reg2                  - set reg=1 if reg1 > reg2 (unsigned),  otherwise set reg1=0
 sgts        reg1, reg2                  - set reg=1 if reg1 > reg2 (signed),  otherwise set reg1=0
 sge         reg1, reg2                  - set reg=1 if reg1 >= reg2 (unsigned),  otherwise set reg1=0
@@ -244,22 +244,22 @@ enum class Opcode {
     BNZ,
     BEQ,
     BNE,
-    BLT,
+    BLT,        // TODO REMOVE
-    BLTS,
+    BLTS,       // TODO REMOVE
     BGT,
     BGTS,
-    BLE,
+    BLE,        // TODO REMOVE
-    BLES,
+    BLES,       // TODO REMOVE
     BGE,
     BGES,
     SEQ,
     SNE,
-    SLT,
+    SLT,        // TODO REMOVE ?
-    SLTS,
+    SLTS,       // TODO REMOVE ?
     SGT,
     SGTS,
-    SLE,
+    SLE,        // TODO REMOVE ?
-    SLES,
+    SLES,       // TODO REMOVE ?
     SGE,
     SGES,