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removed chained comparisons again, because they caused invalid expression evaluations due to changed semantics.

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This commit is contained in:
Irmen de Jong 2024-01-01 16:00:11 +01:00
parent 498841d45d
commit 0e086d788b
6 changed files with 14 additions and 59 deletions
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6
codeOptimizers/src/prog8/optimizer/ConstantFoldingOptimizer.kt
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@ -142,10 +142,8 @@ class ConstantFoldingOptimizer(private val program: Program, private val errors:
// const fold when both operands are a const.
// if in a chained comparison, that one has to be desugared first though.
if(leftconst != null && rightconst != null) {
if((expr.parent as? BinaryExpression)?.isChainedComparison()!=true) {
val result = evaluator.evaluate(leftconst, expr.operator, rightconst)
modifications += IAstModification.ReplaceNode(expr, result, parent)
}
val result = evaluator.evaluate(leftconst, expr.operator, rightconst)
modifications += IAstModification.ReplaceNode(expr, result, parent)
}
if(leftconst==null && rightconst!=null && rightconst.number<0.0) {

14
compiler/src/prog8/compiler/Compiler.kt
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@ -6,9 +6,11 @@ import prog8.ast.Program
import prog8.ast.base.AstException
import prog8.ast.expressions.Expression
import prog8.ast.expressions.NumericLiteral
import prog8.ast.printProgram
import prog8.ast.statements.Directive
import prog8.code.SymbolTableMaker
import prog8.code.ast.PtProgram
import prog8.code.ast.printAst
import prog8.code.core.*
import prog8.code.optimize.optimizeIntermediateAst
import prog8.code.target.*
@ -94,10 +96,10 @@ fun compileProgram(args: CompilerArguments): CompilationResult? {
importedFiles = imported
processAst(program, args.errors, compilationOptions)
if (compilationOptions.optimize) {
// println("*********** COMPILER AST RIGHT BEFORE OPTIMIZING *************")
// printProgram(program)
if (compilationOptions.optimize) {
optimizeAst(
program,
compilationOptions,
@ -105,6 +107,7 @@ fun compileProgram(args: CompilerArguments): CompilationResult? {
BuiltinFunctionsFacade(BuiltinFunctions),
)
}
postprocessAst(program, args.errors, compilationOptions)
// println("*********** COMPILER AST BEFORE ASSEMBLYGEN *************")
@ -120,16 +123,15 @@ fun compileProgram(args: CompilerArguments): CompilationResult? {
program.processAstBeforeAsmGeneration(compilationOptions, args.errors)
args.errors.report()
// println("*********** COMPILER AST RIGHT BEFORE ASM GENERATION *************")
// printProgram(program)
println("*********** COMPILER AST RIGHT BEFORE ASM GENERATION *************")
printProgram(program)
val intermediateAst = IntermediateAstMaker(program, args.errors).transform()
// printAst(intermediateAst, true) { println(it) }
optimizeIntermediateAst(intermediateAst, compilationOptions, args.errors)
args.errors.report()
// println("*********** AST RIGHT BEFORE ASM GENERATION *************")
// printAst(intermediateAst, true, ::println)
println("*********** AST RIGHT BEFORE ASM GENERATION *************")
printAst(intermediateAst, true, ::println)
if(!createAssemblyAndAssemble(intermediateAst, args.errors, compilationOptions)) {
System.err.println("Error in codegeneration or assembler")

24
compiler/src/prog8/compiler/astprocessing/CodeDesugarer.kt
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@ -26,7 +26,6 @@ internal class CodeDesugarer(val program: Program, private val errors: IErrorRep
// - pointer[word] replaced by @(pointer+word)
// - @(&var) and @(&var+1) replaced by lsb(var) and msb(var) if var is a word
// - flatten chained assignments
// - rewrite chained comparisons like i<x<j into i<x and x<j
override fun before(breakStmt: Break, parent: Node): Iterable<IAstModification> {
fun jumpAfter(stmt: Statement): Iterable<IAstModification> {
@ -260,29 +259,6 @@ _after:
return listOf(IAstModification.ReplaceNode(expr, squareCall, parent))
}
// desugar chained comparisons: i < x < j ---> i<x and x<j
// only if i<x or x<j was not written in parentheses! (i<x) < y, i < (x<y) -> leave untouched
if(expr.isChainedComparison()) {
val leftBinExpr = expr.left as? BinaryExpression
if(leftBinExpr!=null) {
if(!leftBinExpr.right.isSimple) {
errors.warn("possible multiple evaluation of subexpression in chained comparison, consider using a temporary variable", leftBinExpr.right.position)
}
val right = BinaryExpression(leftBinExpr.right.copy(), expr.operator, expr.right, leftBinExpr.right.position)
val desugar = BinaryExpression(leftBinExpr, "and", right, expr.position)
return listOf(IAstModification.ReplaceNode(expr, desugar, parent))
}
val rightBinExpr = expr.right as? BinaryExpression
if(rightBinExpr!=null) {
if(!rightBinExpr.left.isSimple) {
errors.warn("possible multiple evaluation of subexpression in chained comparison, consider using a temporary variable", rightBinExpr.left.position)
}
val left = BinaryExpression(expr.left, expr.operator, rightBinExpr.left.copy(), rightBinExpr.left.position)
val desugar = BinaryExpression(left, "and", rightBinExpr, expr.position)
return listOf(IAstModification.ReplaceNode(expr, desugar, parent))
}
}
return noModifications
}

14
compilerAst/src/prog8/ast/expressions/AstExpressions.kt
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@ -35,7 +35,7 @@ sealed class Expression: Node {
is PrefixExpression ->
(other is PrefixExpression && other.operator==operator && other.expression isSameAs expression)
is BinaryExpression -> {
if(other !is BinaryExpression || other.operator!=operator || other.isChainedComparison()!=isChainedComparison())
if(other !is BinaryExpression || other.operator!=operator)
false
else if(operator in AssociativeOperators)
(other.left isSameAs left && other.right isSameAs right) || (other.left isSameAs right && other.right isSameAs left)
@ -182,18 +182,6 @@ class BinaryExpression(
override val isSimple = false
fun isChainedComparison(): Boolean {
if(operator in ComparisonOperators) {
val leftBinExpr = left as? BinaryExpression
if (leftBinExpr != null && !leftBinExpr.insideParentheses && leftBinExpr.operator in ComparisonOperators)
return true
val rightBinExpr = right as? BinaryExpression
if (rightBinExpr != null && !rightBinExpr.insideParentheses && rightBinExpr.operator in ComparisonOperators)
return true
}
return false
}
// binary expression should actually have been optimized away into a single value, before const value was requested...
override fun constValue(program: Program): NumericLiteral? = null

1
docs/source/syntaxreference.rst
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@ -592,7 +592,6 @@ postfix increment and decrement: ``++`` ``--``
comparison: ``==`` ``!=`` ``<`` ``>`` ``<=`` ``>=``
Equality, Inequality, Less-than, Greater-than, Less-or-Equal-than, Greater-or-Equal-than comparisons.
The result is a boolean value 'true' or 'false' (1 or 0).
Note that you can chain comparisons like so: ``i < x < j``, which is the same as ``i<x and x<j``.
logical: ``not`` ``and`` ``or`` ``xor``
These operators are the usual logical operations that are part of a logical expression to reason

14
docs/source/todo.rst
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@ -1,17 +1,6 @@
TODO
====
- Revert or fix current "desugar chained comparisons" it causes problems with if statements (in optimizer).
ubyte @shared n=20
ubyte @shared L1=10
ubyte @shared L2=100
if n < L1 {
;txt.print("bing")
} else {
txt.print("boom") ; no longer triggers
}
...
@ -87,3 +76,6 @@ Other language/syntax features to think about
- add (rom/ram)bank support to romsub. A call will then automatically switch banks, use callfar and something else when in banked ram.
challenges: how to not make this too X16 specific? How does the compiler know what bank to switch (ram/rom)?
How to make it performant when we want to (i.e. NOT have it use callfar/auto bank switching) ?
- chained comparisons `10<x<20` , `x==y==z` (desugars to `10<x and x<20`, `x==y and y==z`)
BUT this needs a new AST node type and rewritten parser rules, because otherwise it changes the semantics
of existing expressions such as if x<y==0 ...