JVM_IR fold safe calls and elvises
This commit is contained in:
Dmitry Petrov
committed by
teamcityserver
teamcityserver
parent
7370d096ee
commit
9325660f06
+162
-68
@@ -31,19 +31,60 @@ val jvmSafeCallFoldingPhase = makeIrFilePhase(
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class JvmSafeCallChainFoldingLowering(val context: JvmBackendContext) : FileLoweringPass {
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// Overall idea here is to represent (possibly chained) safe calls as an if-expression in the form:
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// if ( { val tmp = <safe_receiver>; tmp != null } )
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// <safe_call>
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// else
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// null
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// when {
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// { val tmp = <safe_receiver>; tmp != null } -> <safe_call_result>
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// else -> null
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// }
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// This allows chaining safe calls like 'a?.foo()?.bar()?.qux()':
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// if ( { val tmp1 = a; tmp1 != null } &&
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// { val tmp2 = tmp1.foo(); tmp2 != null } &&
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// { val tmp3 = tmp2.bar(); tmp3 != null }
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// )
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// tmp3.qux()
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// else
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// null
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// This also allows fusing safe calls with elvises (and some other operations).
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// when {
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// { val tmp1 = a; tmp1 != null } &&
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// { val tmp2 = tmp1.foo(); tmp2 != null } &&
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// { val tmp3 = tmp2.bar(); tmp3 != null } ->
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// tmp3.qux()
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// else ->
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// null
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// }
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// Folded safe call always has the following form:
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// when {
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// <safe_call_condition> -> <safe_call_result>
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// else -> null
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// }
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// Note that <safe_call_result> itself might be nullable.
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//
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// Similarly, elvises can be represented in the form:
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// when {
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// { val tmp = <elvis_lhs>; tmp != null } ->
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// tmp
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// else ->
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// <elvis_rhs>
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// }
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// which also allows chaining.
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// Folded and possibly chained elvis has the following form:
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// when {
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// <elvis_condition_1> -> <elvis_lhs_1>
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// ...
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// <elvis_condition_N> -> <elvis_lhs_N>
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// else -> <elvis_rhs>
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// }
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// where <elvis_lhs_k> are guaranteed to be non-null if the corresponding <elvis_condition_k> is true.
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//
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// This allows representing a chain of safe calls and elvises,
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// e.g., 'a?.foo() ?: b?.bar()?.qux() ?: c'
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// in a folded form:
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// when {
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// { val tmp1 = a; tmp1 != null } &&
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// { val tmp2 = tmp1.foo; tmp1 != null } ->
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// tmp2
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// { val tmp3 = b; tmp3 != null } &&
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// { val tmp4 = tmp2.bar(); tmp4 != null } &&
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// { val tmp5 = tmp4.qux(); tmp5 != null } ->
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// tmp5
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// else ->
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// c
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// }
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// which can be further simplified depending on the nullability of subexpressions in 'a?.foo() ?: b?.bar()?.qux() ?: c'.
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// In bytecode this produces a chain of temporary STORE-LOAD and IFNULL checks that can be optimized to a compact sequence
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// of stack operations and IFNULL checks.
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override fun lower(irFile: IrFile) {
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irFile.transformChildrenVoid(Transformer())
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@@ -107,13 +148,13 @@ class JvmSafeCallChainFoldingLowering(val context: JvmBackendContext) : FileLowe
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}
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private fun foldSafeCall(safeCallInfo: SafeCallInfo): IrExpression {
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// Rewrite a safe call in the form:
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// We have a safe call in the form:
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// { // SAFE_CALL
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// val tmp = <safe_receiver>
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// if (tmp == null)
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// null
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// else
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// <call[tmp]>
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// when {
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// tmp == null -> null
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// else -> <safe_call_result>
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// }
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// }
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val safeCallBlock = safeCallInfo.block
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val startOffset = safeCallBlock.startOffset
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@@ -126,18 +167,20 @@ class JvmSafeCallChainFoldingLowering(val context: JvmBackendContext) : FileLowe
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// Chained safe call.
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// If <safe_receiver> is a FOLDED_SAFE_CALL form, rewrite safe call to:
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// { // FOLDED_SAFE_CALL
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// if ( <safe_receiver_condition> && { val tmp = <safe_receiver_result>; tmp != null } )
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// <call[tmp]>
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// else
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// null
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// when {
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// <safe_receiver_condition> && { val tmp = <safe_receiver_result>; tmp != null } ->
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// <safe_call_result>
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// else ->
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// null
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// }
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// }
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// where
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// <safe_receiver> =
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// { // FOLDED_SAFE_CALL
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// if ( <safe_receiver_condition> )
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// <safe_receiver_result>
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// else
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// null
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// when {
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// <safe_receiver_condition> -> <safe_receiver_result>
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// else -> null
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// }
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// }
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val foldedBlock: IrBlock = tmpValInitializer
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val foldedWhen = foldedBlock.statements[0] as IrWhen
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@@ -162,10 +205,12 @@ class JvmSafeCallChainFoldingLowering(val context: JvmBackendContext) : FileLowe
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// Simple safe call.
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// If <safe_receiver> itself is not a FOLDED_SAFE_CALL form, rewrite safe call to:
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// { // FOLDED_SAFE_CALL
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// if ( { val tmp = <safe_receiver>; tmp != null } )
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// <call[tmp]>
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// else
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// null
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// when {
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// { val tmp = <safe_receiver>; tmp != null } ->
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// <safe_call_result>
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// else ->
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// null
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// }
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// }
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val foldedCondition =
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@@ -203,24 +248,37 @@ class JvmSafeCallChainFoldingLowering(val context: JvmBackendContext) : FileLowe
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// Given elvis expression:
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// { // ELVIS
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// val tmp = <elvis_lhs>
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// if (tmp == null)
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// <elvis_rhs>
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// else
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// null
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// when {
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// tmp == null -> <elvis_lhs>
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// else -> null
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// }
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// }
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// where <elvis_lhs> is a folded safe call in the form:
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// { // FOLDED_SAFE_CALL
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// if ( <safe_call_condition> )
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// <safe_call_result>
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// else
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// null
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// when {
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// <safe_call_condition> -> <safe_call_result>
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// else -> null
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// }
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// }
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// rewrite it to
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// { // FOLDED_ELVIS
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// if ( <safe_call_condition> && { val tmp = <safe_call_result>; tmp != null } )
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// tmp
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// else
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// <elvis_rhs>
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// when {
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// <safe_call_condition> && { val tmp = <safe_call_result>; tmp != null } ->
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// tmp
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// else ->
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// <elvis_rhs>
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// }
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// }
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// If <elvis_rhs> is a folded safe call with non-null result, we can inline the underlying 'when':
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// { // FOLDED_ELVIS
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// when {
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// <safe_call_condition> && { val tmp = <safe_call_result>; tmp != null } ->
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// tmp
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// <rhs_safe_call_condition> ->
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// <rhs_safe_call_result>
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// else ->
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// null
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// }
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// }
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val safeCallWhen = elvisLhs.statements[0] as IrWhen
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@@ -236,39 +294,43 @@ class JvmSafeCallChainFoldingLowering(val context: JvmBackendContext) : FileLowe
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irValNotNull(startOffset, endOffset, elvisTmpVal)
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)
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)
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val foldedWhen = IrWhenImpl(
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startOffset, endOffset, elvisType, JvmLoweredStatementOrigin.FOLDED_ELVIS,
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listOf(
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IrBranchImpl(
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startOffset, endOffset,
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irAndAnd(safeCallCondition, foldedConditionPart),
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IrGetValueImpl(startOffset, endOffset, elvisTmpVal.symbol)
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),
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IrBranchImpl(
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startOffset, endOffset,
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irTrue(startOffset, endOffset),
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elvisInfo.elvisRhs
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)
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val branches = ArrayList<IrBranch>()
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branches.add(
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IrBranchImpl(
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startOffset, endOffset,
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irAndAnd(safeCallCondition, foldedConditionPart),
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IrGetValueImpl(startOffset, endOffset, elvisTmpVal.symbol)
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)
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)
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return foldedWhen.wrapWithBlock(JvmLoweredStatementOrigin.FOLDED_ELVIS)
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val elvisRhs = elvisInfo.elvisRhs
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if (elvisRhs.isFoldedSafeCallWithNonNullResult()) {
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val rhsInnerWhen = (elvisRhs as IrBlock).statements[0] as IrWhen
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branches.addAll(rhsInnerWhen.branches)
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} else {
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branches.add(IrBranchImpl(startOffset, endOffset, irTrue(startOffset, endOffset), elvisInfo.elvisRhs))
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}
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return IrWhenImpl(startOffset, endOffset, elvisType, JvmLoweredStatementOrigin.FOLDED_ELVIS, branches)
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.wrapWithBlock(JvmLoweredStatementOrigin.FOLDED_ELVIS)
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}
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elvisLhs is IrBlock && elvisLhs.origin == JvmLoweredStatementOrigin.FOLDED_ELVIS -> {
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// Append branches to the inner elvis:
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// val t = { // FOLDED_ELVIS
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// if (...) ...
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// else if ...
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// else <innerElvisRhs>
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// when {
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// ... <innerElvisBranches> ...
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// else -> <innerElvisRhs>
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// }
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// }
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// when {
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// t == null -> <outerElvisRhs>
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// else -> t
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// }
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// if (t != null) t else <outerElvisRhs>
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// =>
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// { // FOLDED_ELVIS
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// if (...) ...
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// else if ...
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// else if ( { val t = <innerElvisRhs>; t != null } )
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// t
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// else
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// <outerElvisRhs>
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// when {
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// ... <innerElvisBranches> ...
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// { val t = <innerElvisRhs>; t != null } -> t
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// else -> <outerElvisRhs>
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// }
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// }
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// TODO maybe we can do somewhat better if we analyze innerElvisRhs as well
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val innerElvisWhen = elvisLhs.statements[0] as IrWhen
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@@ -295,11 +357,45 @@ class JvmSafeCallChainFoldingLowering(val context: JvmBackendContext) : FileLowe
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return innerElvisWhen.wrapWithBlock(JvmLoweredStatementOrigin.FOLDED_ELVIS)
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}
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else -> {
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return elvisInfo.block
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// Plain elvis.
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// { // ELVIS
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// val tmp = <lhs>
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// when {
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// tmp == null -> <rhs>
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// else -> tmp
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// }
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// }
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// Fold it as:
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// { // FOLDED_ELVIS
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// when {
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// { val tmp = <lhs>; tmp != null } -> tmp
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// else -> rhs
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// }
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// }
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val newCondition = IrCompositeImpl(
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startOffset, endOffset, context.irBuiltIns.booleanType, null,
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listOf(elvisTmpVal, irValNotNull(startOffset, endOffset, elvisTmpVal))
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)
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val foldedWhen = IrWhenImpl(
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startOffset, endOffset, elvisType, JvmLoweredStatementOrigin.FOLDED_ELVIS,
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listOf(
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IrBranchImpl(startOffset, endOffset, newCondition, IrGetValueImpl(startOffset, endOffset, elvisTmpVal.symbol)),
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IrBranchImpl(startOffset, endOffset, irTrue(startOffset, endOffset), elvisInfo.elvisRhs)
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)
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)
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return foldedWhen.wrapWithBlock(JvmLoweredStatementOrigin.FOLDED_ELVIS)
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}
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}
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}
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private fun IrExpression.isFoldedSafeCallWithNonNullResult(): Boolean {
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if (this !is IrBlock) return false
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if (this.origin != JvmLoweredStatementOrigin.FOLDED_SAFE_CALL) return false
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val innerWhen = this.statements[0] as? IrWhen ?: return false
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val safeCallResult = innerWhen.branches[0].result
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return !safeCallResult.type.isNullable()
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}
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override fun visitCall(expression: IrCall): IrExpression {
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expression.transformChildrenVoid()
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@@ -330,10 +426,8 @@ class JvmSafeCallChainFoldingLowering(val context: JvmBackendContext) : FileLowe
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return safeCallWhen.wrapWithBlock(origin = null)
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}
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}
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return expression
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}
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}
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}
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