SpillSequenceSpiller – preserve ref BoundConditionalOperator in pre…

…sence of spilling in its either branch (#74310) Fixes #74115.
dotnet · Jul 16, 2024 · 432b124 · 432b124
1 parent 06ee35f
commit 432b124
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diff --git a/src/Compilers/CSharp/Portable/Lowering/SpillSequenceSpiller.cs b/src/Compilers/CSharp/Portable/Lowering/SpillSequenceSpiller.cs
@@ -1130,7 +1130,7 @@ public override BoundNode VisitConditionalOperator(BoundConditionalOperator node
 
                 return conditionBuilder.Update(_F.Default(node.Type));
             }
-            else
+            else if (!node.IsRef)
             {
                 var tmp = _F.SynthesizedLocal(node.Type, kind: SynthesizedLocalKind.Spill, syntax: _F.Syntax);
 
@@ -1142,6 +1142,33 @@ public override BoundNode VisitConditionalOperator(BoundConditionalOperator node
 
                 return conditionBuilder.Update(_F.Local(tmp));
             }
+            else
+            {
+                Debug.Assert(condition.Type.SpecialType == SpecialType.System_Boolean);
+
+                // 1. Capture the boolean value (the condition) in a temp
+                var tmp = _F.SynthesizedLocal(condition.Type, kind: SynthesizedLocalKind.Spill, syntax: _F.Syntax);
+
+                conditionBuilder.AddLocal(tmp);
+                conditionBuilder.AddStatement(_F.Assignment(_F.Local(tmp), condition));
+                condition = _F.Local(tmp);
+
+                // 2. Conditionally execute side-effects from the builders based on the temp 
+                conditionBuilder.AddLocals(consequenceBuilder.GetLocals());
+                conditionBuilder.AddLocals(alternativeBuilder.GetLocals());
+
+                conditionBuilder.AddStatement(
+                    _F.If(condition,
+                        _F.StatementList(consequenceBuilder.GetStatements()),
+                        _F.StatementList(alternativeBuilder.GetStatements())));
+
+                consequenceBuilder.Free();
+                alternativeBuilder.Free();
+
+                // 3. Use updated conditional operator as the result. Note, we are using the captured temp as its condition,
+                // plus rewritten consequence and alternative.
+                return conditionBuilder.Update(node.Update(node.IsRef, condition, consequence, alternative, node.ConstantValueOpt, node.NaturalTypeOpt, node.WasTargetTyped, node.Type));
+            }
         }
 
         public override BoundNode VisitConversion(BoundConversion node)