Spill stack for inline functions only if it's required

Stack should be spilled before inline function call and restored after
call only if one of the following conditions is met:
- inline function is a suspend function
- inline function has try-catch blocks
- inline function has loops (backward jumps)

Note that there're quite some "simple" inline functions in Kotlin stdlib
besides run/let/with/apply. For example, many string operations are
implemented as inline wrappers over Java method calls.

compiler/backend/src/org/jetbrains/kotlin/codegen/inline/InlineCodegen.kt

@@ -20,7 +20,8 @@ import com.intellij.psi.PsiElement
 import com.intellij.util.ArrayUtil
 import org.jetbrains.kotlin.builtins.BuiltInsPackageFragment
 import org.jetbrains.kotlin.codegen.*
-import org.jetbrains.kotlin.codegen.AsmUtil.*
+import org.jetbrains.kotlin.codegen.AsmUtil.getMethodAsmFlags
+import org.jetbrains.kotlin.codegen.AsmUtil.isPrimitive
 import org.jetbrains.kotlin.codegen.coroutines.createMethodNodeForSuspendCoroutineOrReturn
 import org.jetbrains.kotlin.codegen.coroutines.isBuiltInSuspendCoroutineOrReturnInJvm
 import org.jetbrains.kotlin.codegen.intrinsics.bytecode
@@ -29,7 +30,9 @@ import org.jetbrains.kotlin.codegen.state.GenerationState
 import org.jetbrains.kotlin.descriptors.*
 import org.jetbrains.kotlin.descriptors.annotations.isInlineOnly
 import org.jetbrains.kotlin.name.Name
-import org.jetbrains.kotlin.psi.*
+import org.jetbrains.kotlin.psi.KtCallableReferenceExpression
+import org.jetbrains.kotlin.psi.KtExpression
+import org.jetbrains.kotlin.psi.KtPsiUtil
 import org.jetbrains.kotlin.renderer.DescriptorRenderer
 import org.jetbrains.kotlin.resolve.BindingContext
 import org.jetbrains.kotlin.resolve.DescriptorToSourceUtils
@@ -47,13 +50,15 @@ import org.jetbrains.kotlin.serialization.deserialization.descriptors.Deserializ
 import org.jetbrains.kotlin.types.expressions.DoubleColonLHS
 import org.jetbrains.kotlin.types.expressions.ExpressionTypingUtils.isFunctionLiteral
 import org.jetbrains.kotlin.types.expressions.LabelResolver
+import org.jetbrains.kotlin.utils.DFS
+import org.jetbrains.kotlin.utils.addIfNotNull
 import org.jetbrains.org.objectweb.asm.Opcodes
 import org.jetbrains.org.objectweb.asm.Type
 import org.jetbrains.org.objectweb.asm.commons.InstructionAdapter
 import org.jetbrains.org.objectweb.asm.commons.Method
-import org.jetbrains.org.objectweb.asm.tree.AbstractInsnNode
+import org.jetbrains.org.objectweb.asm.tree.*
-import org.jetbrains.org.objectweb.asm.tree.MethodNode
 import java.util.*
+import kotlin.collections.HashSet
 
 abstract class InlineCodegen<out T: BaseExpressionCodegen>(
         protected val codegen: T,
@@ -179,6 +184,46 @@ abstract class InlineCodegen<out T: BaseExpressionCodegen>(
         }
     }
 
+    private fun canSkipStackSpillingOnInline(methodNode: MethodNode): Boolean {
+        // Stack spilling before inline function 'f' call is required if:
+        //  - 'f' is a suspend function
+        //  - 'f' has try-catch blocks
+        //  - 'f' has loops
+        //
+        // Instead of checking for loops precisely, we just check if there are any backward jumps -
+        // that is, a jump from instruction #i to instruction #j where j < i
+
+        if (functionDescriptor.isSuspend) return false
+        if (methodNode.tryCatchBlocks.isNotEmpty()) return false
+
+        fun isBackwardJump(fromIndex: Int, toLabel: LabelNode) =
+                methodNode.instructions.indexOf(toLabel) < fromIndex
+
+        val insns = methodNode.instructions.toArray()
+        for (i in insns.indices) {
+            val insn = insns[i]
+            when (insn) {
+                is JumpInsnNode ->
+                    if (isBackwardJump(i, insn.label)) return false
+
+                is LookupSwitchInsnNode -> {
+                    insn.dflt?.let {
+                        if (isBackwardJump(i, it)) return false
+                    }
+                    if (insn.labels.any { isBackwardJump(i, it) }) return false
+                }
+
+                is TableSwitchInsnNode -> {
+                    insn.dflt?.let {
+                        if (isBackwardJump(i, it)) return false
+                    }
+                    if (insn.labels.any { isBackwardJump(i, it) }) return false
+                }
+            }
+        }
+
+        return true
+    }
 
     protected fun inlineCall(nodeAndSmap: SMAPAndMethodNode, callDefault: Boolean): InlineResult {
         assert(delayedHiddenWriting == null) { "'putHiddenParamsIntoLocals' should be called after 'processAndPutHiddenParameters(true)'" }
@@ -201,7 +246,11 @@ abstract class InlineCodegen<out T: BaseExpressionCodegen>(
         //through generation captured parameters will be added to invocationParamBuilder
         putClosureParametersOnStack()
 
-        addInlineMarker(codegen.v, true)
+        val shouldSpillStack = !canSkipStackSpillingOnInline(node)
+
+        if (shouldSpillStack) {
+            addInlineMarker(codegen.v, true)
+        }
 
         val parameters = invocationParamBuilder.buildParameters()
 
@@ -239,7 +288,9 @@ abstract class InlineCodegen<out T: BaseExpressionCodegen>(
 
         adapter.accept(MethodBodyVisitor(codegen.v))
 
-        addInlineMarker(codegen.v, false)
+        if (shouldSpillStack) {
+            addInlineMarker(codegen.v, false)
+        }
 
         defaultSourceMapper.callSiteMarker = null
 

compiler/testData/codegen/bytecodeText/storeStackBeforeInline/differentTypes.kt

@@ -1,4 +1,9 @@
-inline fun bar(x: Int, y: Long, z: Byte, s: String) = x.toString() + y.toString() + z.toString() + s
+inline fun <T> runAfterLoop(fn: () -> T): T {
+    for (i in 1..2);
+    return fn()
+}
+
+inline fun bar(x: Int, y: Long, z: Byte, s: String) = runAfterLoop { x.toString() + y.toString() + z.toString() + s }
 
 fun foobar(x: Int, y: Long, s: String, z: Byte) = x.toString() + y.toString() + s + z.toString()
 
@@ -6,10 +11,10 @@ fun foo() : String {
     return foobar(1, 2L, bar(3, 4L, 5.toByte(), "6"), 7.toByte())
 }
 
-// 3 ISTORE
+// 9 ISTORE
-// 7 ILOAD
+// 13 ILOAD
 // 2 ASTORE
-// 6 ALOAD
+// 8 ALOAD
 // 2 LSTORE
 // 4 LLOAD
 // 1 MAXLOCALS = 10

compiler/testData/codegen/bytecodeText/storeStackBeforeInline/primitiveMerge.kt

@@ -1,17 +1,22 @@
+inline fun <T> runAfterLoop(fn: () -> T): T {
+    for (i in 1..2);
+    return fn()
+}
+
 fun bar() : Boolean = true
 
 fun foobar(x: Boolean, y: String, z: String) = x.toString() + y + z
 
-inline fun foo() = "-"
+inline fun foo() = runAfterLoop { "-" }
 
 fun test() {
     val result = foobar(if (1 == 1) true else bar(), foo(), "OK")
 }
 
-// 1 ISTORE
+// 7 ISTORE
-// 2 ILOAD
+// 8 ILOAD
 // 2 ASTORE
-// 5 ALOAD
+// 7 ALOAD
 // 1 MAXLOCALS = 3
 // 1 MAXLOCALS = 4
 // 0 InlineMarker

compiler/testData/codegen/bytecodeText/storeStackBeforeInline/simple.kt

@@ -9,6 +9,6 @@ fun foo() : Int {
     return foobar(1, bar(2), 3)
 }
 
-// 3 ISTORE
+// 1 ISTORE
-// 7 ILOAD
+// 5 ILOAD
 // 0 InlineMarker

compiler/testData/codegen/bytecodeText/storeStackBeforeInline/unreachableMarker.kt

@@ -1,5 +1,10 @@
+inline fun <T> runAfterLoop(fn: () -> T): T {
+    for (i in 1..2);
+    return fn()
+}
+
 inline fun bar(block: () -> String) : String {
-    return block()
+    return runAfterLoop(block)
 }
 
 inline fun bar2() : String {
@@ -16,6 +21,6 @@ fun foo() : String {
     )
 }
 
-// 10 ALOAD
+// 12 ALOAD
 // 2 ASTORE
 // 0 InlineMarker

compiler/testData/codegen/bytecodeText/storeStackBeforeInline/withLambda.kt

@@ -1,4 +1,10 @@
-inline fun bar(x: String, block: (String) -> String) = "def" + block(x)
+inline fun <T> runAfterLoop(fn: () -> T): T {
+    for (i in 1..2);
+    return fn()
+}
+
+inline fun bar(x: String, block: (String) -> String) = runAfterLoop { "def" + block(x) }
+
 fun foobar(x: String, y: String, z: String) = x + y + z
 
 fun foo() : String {
@@ -6,6 +12,6 @@ fun foo() : String {
 }
 
 // 6 ASTORE
-// 16 ALOAD
+// 18 ALOAD
 // 1 MAXLOCALS = 7
 // 0 InlineMarker