[FIR2IR] Don't emit empty body of while/do_while loop

Merge-request: KT-MR-12283
Merged-by: Vladimir Sukharev <Vladimir.Sukharev@jetbrains.com>

compiler/fir/fir2ir/src/org/jetbrains/kotlin/fir/backend/Fir2IrVisitor.kt

@@ -1303,7 +1303,9 @@ class Fir2IrVisitor(
             ).apply {
                 loopMap[doWhileLoop] = this
                 label = doWhileLoop.label?.name
-                body = doWhileLoop.block.convertToIrExpressionOrBlock(origin)
+                body = runUnless(doWhileLoop.block is FirEmptyExpressionBlock) {
+                    doWhileLoop.block.convertToIrExpressionOrBlock(origin)
+                }
                 condition = convertToIrExpression(doWhileLoop.condition)
                 loopMap.remove(doWhileLoop)
             }
@@ -1324,7 +1326,8 @@ class Fir2IrVisitor(
                 loopMap[whileLoop] = this
                 label = whileLoop.label?.name
                 condition = convertToIrExpression(whileLoop.condition)
-                body = if (isForLoop) {
+                body = runUnless(firLoopBody is FirEmptyExpressionBlock) {
+                    if (isForLoop) {
                         /*
                          * for loops in IR must have their body in the exact following form
                          * because some of the lowerings (e.g. `ForLoopLowering`) expect it:
@@ -1368,6 +1371,7 @@ class Fir2IrVisitor(
                     } else {
                         firLoopBody.convertToIrExpressionOrBlock(origin)
                     }
+                }
                 loopMap.remove(whileLoop)
             }
         }.also {

compiler/testData/ir/irText/expressions/breakContinueInLoopHeader.fir.ir.txt

@@ -18,7 +18,6 @@ FILE fqName:<root> fileName:/breakContinueInLoopHeader.kt
                 BRANCH
                   if: CONST Boolean type=kotlin.Boolean value=true
                   then: GET_VAR 'val tmp_0: kotlin.Boolean? declared in <root>.test1' type=kotlin.Boolean? origin=null
-            body: BLOCK type=kotlin.Unit origin=null
   FUN name:test2 visibility:public modality:FINAL <> (c:kotlin.Boolean?) returnType:kotlin.Unit
     VALUE_PARAMETER name:c index:0 type:kotlin.Boolean?
     BLOCK_BODY
@@ -38,7 +37,6 @@ FILE fqName:<root> fileName:/breakContinueInLoopHeader.kt
                 BRANCH
                   if: CONST Boolean type=kotlin.Boolean value=true
                   then: GET_VAR 'val tmp_1: kotlin.Boolean? declared in <root>.test2' type=kotlin.Boolean? origin=null
-            body: BLOCK type=kotlin.Unit origin=null
   FUN name:test3 visibility:public modality:FINAL <> (ss:kotlin.collections.List<kotlin.String>?) returnType:kotlin.Unit
     VALUE_PARAMETER name:ss index:0 type:kotlin.collections.List<kotlin.String>?
     BLOCK_BODY

compiler/testData/ir/irText/expressions/breakContinueInLoopHeader.fir.kt.txt

@@ -6,8 +6,7 @@ fun test1(c: Boolean?) {
         EQEQ(arg0 = <elvis>, arg1 = null) -> break@L
         else -> <elvis>
       }
-    }) { // BLOCK
+    })
-    }
   }
 }
 
@@ -19,8 +18,7 @@ fun test2(c: Boolean?) {
         EQEQ(arg0 = <elvis>, arg1 = null) -> continue@L
         else -> <elvis>
       }
-    }) { // BLOCK
+    })
-    }
   }
 }
 

compiler/testData/ir/irText/expressions/whileDoWhile.fir.ir.txt

@@ -7,7 +7,6 @@ FILE fqName:<root> fileName:/whileDoWhile.kt
         condition: CALL 'public final fun less (arg0: kotlin.Int, arg1: kotlin.Int): kotlin.Boolean declared in kotlin.internal.ir' type=kotlin.Boolean origin=LT
           arg0: GET_VAR 'var x: kotlin.Int declared in <root>.test' type=kotlin.Int origin=null
           arg1: CONST Int type=kotlin.Int value=0
-        body: BLOCK type=kotlin.Unit origin=null
       WHILE label=null origin=WHILE_LOOP
         condition: CALL 'public final fun less (arg0: kotlin.Int, arg1: kotlin.Int): kotlin.Boolean declared in kotlin.internal.ir' type=kotlin.Boolean origin=LT
           arg0: GET_VAR 'var x: kotlin.Int declared in <root>.test' type=kotlin.Int origin=null
@@ -33,10 +32,15 @@ FILE fqName:<root> fileName:/whileDoWhile.kt
             GET_VAR 'val tmp_1: kotlin.Int declared in <root>.test' type=kotlin.Int origin=null
       BLOCK type=kotlin.Unit origin=null
         DO_WHILE label=null origin=DO_WHILE_LOOP
-          body: COMPOSITE type=kotlin.Unit origin=null
           condition: CALL 'public final fun less (arg0: kotlin.Int, arg1: kotlin.Int): kotlin.Boolean declared in kotlin.internal.ir' type=kotlin.Boolean origin=LT
             arg0: GET_VAR 'var x: kotlin.Int declared in <root>.test' type=kotlin.Int origin=null
             arg1: CONST Int type=kotlin.Int value=0
+      BLOCK type=kotlin.Unit origin=null
+        DO_WHILE label=null origin=DO_WHILE_LOOP
+          body: COMPOSITE type=kotlin.Unit origin=null
+          condition: CALL 'public final fun less (arg0: kotlin.Int, arg1: kotlin.Int): kotlin.Boolean declared in kotlin.internal.ir' type=kotlin.Boolean origin=LT
+            arg0: GET_VAR 'var x: kotlin.Int declared in <root>.test' type=kotlin.Int origin=null
+            arg1: CONST Int type=kotlin.Int value=7
       BLOCK type=kotlin.Unit origin=null
         DO_WHILE label=null origin=DO_WHILE_LOOP
           body: BLOCK type=kotlin.Int origin=POSTFIX_INCR

compiler/testData/ir/irText/expressions/whileDoWhile.fir.kt.txt

@@ -1,7 +1,6 @@
 fun test() {
   var x: Int = 0
-  while (less(arg0 = x, arg1 = 0)) { // BLOCK
+  while (less(arg0 = x, arg1 = 0))
-  }
   while (less(arg0 = x, arg1 = 5)) { // BLOCK
     val <unary>: Int = x
     x = <unary>.inc()
@@ -14,9 +13,12 @@ fun test() {
       <unary>
     }
   }
+  { // BLOCK
+    do    while (less(arg0 = x, arg1 = 0))
+  }
   { // BLOCK
     do// COMPOSITE {
-    // }    while (less(arg0 = x, arg1 = 0))
+    // }    while (less(arg0 = x, arg1 = 7))
   }
   { // BLOCK
     do{ // BLOCK

compiler/testData/ir/irText/expressions/whileDoWhile.ir.txt

@@ -37,6 +37,12 @@ FILE fqName:<root> fileName:/whileDoWhile.kt
           condition: CALL 'public final fun less (arg0: kotlin.Int, arg1: kotlin.Int): kotlin.Boolean declared in kotlin.internal.ir' type=kotlin.Boolean origin=LT
             arg0: GET_VAR 'var x: kotlin.Int declared in <root>.test' type=kotlin.Int origin=null
             arg1: CONST Int type=kotlin.Int value=0
+      BLOCK type=kotlin.Unit origin=null
+        DO_WHILE label=null origin=DO_WHILE_LOOP
+          body: COMPOSITE type=kotlin.Unit origin=null
+          condition: CALL 'public final fun less (arg0: kotlin.Int, arg1: kotlin.Int): kotlin.Boolean declared in kotlin.internal.ir' type=kotlin.Boolean origin=LT
+            arg0: GET_VAR 'var x: kotlin.Int declared in <root>.test' type=kotlin.Int origin=null
+            arg1: CONST Int type=kotlin.Int value=7
       BLOCK type=kotlin.Unit origin=null
         DO_WHILE label=null origin=DO_WHILE_LOOP
           body: TYPE_OP type=kotlin.Unit origin=IMPLICIT_COERCION_TO_UNIT typeOperand=kotlin.Unit

compiler/testData/ir/irText/expressions/whileDoWhile.kt

@@ -4,6 +4,7 @@ fun test() {
     while (x < 5) x++
     while (x < 10) { x++ }
     do while (x < 0)
+    do {} while (x < 7)
     do x++ while (x < 15)
     do { x ++ } while (x < 20)
 }

compiler/testData/ir/irText/expressions/whileDoWhile.kt.txt

@@ -16,6 +16,10 @@ fun test() {
   { // BLOCK
     do    while (less(arg0 = x, arg1 = 0))
   }
+  { // BLOCK
+    do// COMPOSITE {
+    // }    while (less(arg0 = x, arg1 = 7))
+  }
   { // BLOCK
     do{ // BLOCK
       val tmp2: Int = x