SimplifyBuiltin: ignore debug_step and debug_value when checking for side-effects in the callee of a builtin.once

Author: eeckstein

SwiftCompilerSources/Sources/Optimizer/InstructionSimplification/SimplifyBuiltin.swift

@@ -81,7 +81,7 @@ private extension BuiltinInst {
     // because memory effects are not computed in the Onone pipeline, yet.
     // This is no problem because the callee (usually a global init function )is mostly very small,
     // or contains the side-effect instruction `alloc_global` right at the beginning.
-    if callee.instructions.contains(where: { $0.mayReadOrWriteMemory || $0.hasUnspecifiedSideEffects }) {
+    if callee.instructions.contains(where: hasSideEffectForBuiltinOnce) {
       return
     }
     context.erase(instruction: self)
@@ -133,6 +133,16 @@ private extension BuiltinInst {
   }
 }
 
+private func hasSideEffectForBuiltinOnce(_ instruction: Instruction) -> Bool {
+  switch instruction {
+  case is DebugStepInst, is DebugValueInst:
+    return false
+  default:
+    return instruction.mayReadOrWriteMemory ||
+           instruction.hasUnspecifiedSideEffects
+  }
+}
+
 private func typesOfValuesAreEqual(_ lhs: Value, _ rhs: Value, in function: Function) -> Bool? {
   if lhs == rhs {
     return true

test/SILOptimizer/simplify_builtin.sil

@@ -274,6 +274,8 @@ bb0:
   %1 = global_addr @g : $*Int32
   %2 = integer_literal $Builtin.Int32, 10
   %3 = struct $Int32 (%2 : $Builtin.Int32)
+  debug_step
+  debug_value %1 : $*Int32
   %6 = tuple ()
   return %6 : $()
 }