Add SILFunction::preserveDebugInfo()

Author: atrick

include/swift/SIL/SILFunction.h

@@ -839,6 +839,15 @@ class SILFunction
     OptMode = unsigned(mode);
   }
 
+  /// True if debug information must be preserved (-Onone).
+  ///
+  /// If this is false (-O), then the presence of debug info must not affect the
+  /// outcome of any transformations.
+  ///
+  /// Typically used to determine whether a debug_value is a normal SSA use or
+  /// incidental use.
+  bool preserveDebugInfo() const;
+
   PerformanceConstraints getPerfConstraints() const { return perfConstraints; }
 
   void setPerfConstraints(PerformanceConstraints perfConstr) {

lib/SIL/IR/SILFunction.cpp

@@ -281,6 +281,10 @@ OptimizationMode SILFunction::getEffectiveOptimizationMode() const {
   return getModule().getOptions().OptMode;
 }
 
+bool SILFunction::preserveDebugInfo() const {
+  return getEffectiveOptimizationMode() <= OptimizationMode::NoOptimization;
+}
+
 bool SILFunction::shouldOptimize() const {
   return getEffectiveOptimizationMode() != OptimizationMode::NoOptimization;
 }