improves switch code generation (#233)

- use better label variable names for end of switch / each switch section - does not emit a jump to the end of the switch at the last case before a 'default' - adds individual switch sections to snippet / cecilified mapping
adrianoc · Jul 28, 2023 · 628214e · 628214e
1 parent 214eb89
commit 628214e
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Showing 3 changed files with 34 additions and 22 deletions.
diff --git a/Cecilifier.Core.Tests/Tests/Unit/Miscellaneous.Statements.cs b/Cecilifier.Core.Tests/Tests/Unit/Miscellaneous.Statements.cs
@@ -113,35 +113,35 @@ void M()
             \s+//case 1: \(condition\)
             \s+il_M_7.Emit\(OpCodes.Ldloc, l_switchCondition_13\);
             \s+il_M_7.Emit\(OpCodes.Ldc_I4, 1\);
-            \s+il_M_7.Emit\(OpCodes.Beq_S, nop_15\);
+            \s+il_M_7.Emit\(OpCodes.Beq_S, lbl_caseCode_0_15\);
             
             \s+//case 2: \(condition\)
             \s+il_M_7.Emit\(OpCodes.Ldloc, l_switchCondition_13\);
             \s+il_M_7.Emit\(OpCodes.Ldc_I4, 2\);
-            \s+il_M_7.Emit\(OpCodes.Beq_S, nop_16\);
+            \s+il_M_7.Emit\(OpCodes.Beq_S, lbl_caseCode_1_16\);
             
-            \s+il_M_7.Emit\(OpCodes.Br, nop_17\);
-            \s+il_M_7.Emit\(OpCodes.Br, nop_14\);
+            \s+il_M_7.Emit\(OpCodes.Br, lbl_caseCode_2_17\);
+            \s+il_M_7.Emit\(OpCodes.Br, lbl_endOfSwitch_14\);
             \s+//case 1: \(code\)
-            \s+il_M_7.Append\(nop_15\);
+            \s+il_M_7.Append\(lbl_caseCode_0_15\);
             \s+il_M_7.Emit\(OpCodes.Ldstr, "C1"\);
             \s+il_M_7.Emit\(OpCodes.Call, .+System.Console.+WriteLine.+\);
-            \s+il_M_7.Emit\(OpCodes.Br, nop_14\);
+            \s+il_M_7.Emit\(OpCodes.Br, lbl_endOfSwitch_14\);
             
             \s+//case 2: \(code\)
-            \s+il_M_7.Append\(nop_16\);
+            \s+il_M_7.Append\(lbl_caseCode_1_16\);
             \s+il_M_7.Emit\(OpCodes.Ldstr, "C2"\);
             \s+il_M_7.Emit\(OpCodes.Call, .+System.Console.+WriteLine.+\);
-            \s+il_M_7.Emit\(OpCodes.Br, nop_14\);
+            \s+il_M_7.Emit\(OpCodes.Br, lbl_endOfSwitch_14\);
             
             \s+//default: \(code\)
-            \s+il_M_7.Append\(nop_17\);
+            \s+il_M_7.Append\(lbl_caseCode_2_17\);
             \s+il_M_7.Emit\(OpCodes.Ldstr, "CD"\);
             \s+il_M_7.Emit\(OpCodes.Call, .+System.Console.+WriteLine.+\);
-            \s+il_M_7.Emit\(OpCodes.Br, nop_14\);
+            \s+il_M_7.Emit\(OpCodes.Br, lbl_endOfSwitch_14\);
             
             \s+//End of switch
-            \s+il_M_7.Append\(nop_14\);
+            \s+il_M_7.Append\(lbl_endOfSwitch_14\);
             """));
     }
 

diff --git a/Cecilifier.Core/AST/StatementVisitor.cs b/Cecilifier.Core/AST/StatementVisitor.cs
@@ -79,47 +79,58 @@ public override void VisitSwitchStatement(SwitchStatementSyntax node)
             Context.EmitCilInstruction(_ilVar, OpCodes.Stloc, evaluatedExpressionVariable); // stores evaluated expression in local var
 
             // Add label to end of switch
-            var endOfSwitchLabel = CreateCilInstruction(_ilVar, OpCodes.Nop);
+            var endOfSwitchLabel = CreateCilInstruction(_ilVar, Context.Naming.Label("endOfSwitch"), OpCodes.Nop);
             breakToInstructionVars.Push(endOfSwitchLabel);
 
             // Write the switch conditions.
-            var nextTestLabels = node.Sections.Select(_ => CreateCilInstruction(_ilVar, OpCodes.Nop)).ToArray();
+            var nextTestLabels = node.Sections.Select( (_, index) =>
+            {
+                var labelName = Context.Naming.Label($"caseCode_{index}");
+                CreateCilInstruction(_ilVar, labelName, OpCodes.Nop);
+                return labelName;
+            }).ToArray();
+
+            var hasDefault = false;
             var currentLabelIndex = 0;
             foreach (var switchSection in node.Sections)
             {
                 if (switchSection.Labels.First().Kind() == SyntaxKind.DefaultSwitchLabel)
                 {
                     Context.EmitCilInstruction(_ilVar, OpCodes.Br, nextTestLabels[currentLabelIndex]);
+                    hasDefault = true;
                     continue;
                 }
 
                 foreach (var sectionLabel in switchSection.Labels)
                 {
+                    using var _ = LineInformationTracker.Track(Context, sectionLabel);
+
+                    Context.WriteNewLine();
                     Context.WriteComment($"{sectionLabel.ToString()} (condition)");
                     Context.EmitCilInstruction(_ilVar, OpCodes.Ldloc, evaluatedExpressionVariable);
                     ExpressionVisitor.Visit(Context, _ilVar, sectionLabel);
-                    string operand = nextTestLabels[currentLabelIndex];
-                    Context.EmitCilInstruction(_ilVar, OpCodes.Beq_S, operand);
-                    Context.WriteNewLine();
+                    Context.EmitCilInstruction(_ilVar, OpCodes.Beq_S, nextTestLabels[currentLabelIndex]);
                 }
                 currentLabelIndex++;
             }
-
-            // if at runtime the code hits this point it means none of the labels matched.
-            // so, just jump to the end of the switch.
-            Context.EmitCilInstruction(_ilVar, OpCodes.Br, endOfSwitchLabel);
+
+            // if at runtime the code hits this point and the switch does not have a default section
+            // it means none of the labels matched so just jump to the end of the switch.
+            if (!hasDefault)
+                Context.EmitCilInstruction(_ilVar, OpCodes.Br, endOfSwitchLabel);
 
             // Write the statements for each switch section...
             currentLabelIndex = 0;
             foreach (var switchSection in node.Sections)
             {
+                using var _ = LineInformationTracker.Track(Context, switchSection);
+                Context.WriteNewLine();
                 Context.WriteComment($"{switchSection.Labels.First().ToString()} (code)");
                 AddCecilExpression($"{_ilVar}.Append({nextTestLabels[currentLabelIndex]});");
                 foreach (var statement in switchSection.Statements)
                 {
                     statement.Accept(this);
                 }
-                Context.WriteNewLine();
                 currentLabelIndex++;
             }
 

diff --git a/Cecilifier.Core/AST/SyntaxWalkerBase.cs b/Cecilifier.Core/AST/SyntaxWalkerBase.cs
@@ -110,10 +110,11 @@ protected string CreateCilInstruction(string ilVar, OpCode opCode, object operan
             return instVar;
         }
 
-        protected void CreateCilInstruction(string ilVar, string instVar, OpCode opCode, object operand = null)
+        protected string CreateCilInstruction(string ilVar, string instVar, OpCode opCode, object operand = null)
         {
             var operandStr = operand == null ? string.Empty : $", {operand}";
             AddCecilExpression($"var {instVar} = {ilVar}.Create({opCode.ConstantName()}{operandStr});");
+            return instVar;
         }
 
         protected void LoadLiteralValue(string ilVar, ITypeSymbol type, string value, bool isTargetOfCall, SyntaxNode parent)