[DebugInfo] Salvage integer literals

Author: Snowy1803

lib/SILOptimizer/Utils/InstOptUtils.cpp

@@ -1964,6 +1964,25 @@ void swift::salvageDebugInfo(SILInstruction *I) {
         }
       }
   }
+
+  if (auto *IL = dyn_cast<IntegerLiteralInst>(I)) {
+    APInt value = IL->getValue();
+    const SILDIExprElement ExprElements[2] = {
+      SILDIExprElement::createOperator(value.isNegative() ?
+        SILDIExprOperator::ConstSInt : SILDIExprOperator::ConstUInt),
+      SILDIExprElement::createConstInt(value.getLimitedValue()),
+    };
+    for (Operand *U : getDebugUses(IL)) {
+      auto *DbgInst = cast<DebugValueInst>(U->getUser());
+      auto VarInfo = DbgInst->getVarInfo();
+      if (!VarInfo)
+        continue;
+      VarInfo->DIExpr.prependElements(ExprElements);
+      // Create a new debug_value, with undef, and the correct const int
+      SILBuilder(DbgInst, DbgInst->getDebugScope())
+        .createDebugValue(DbgInst->getLoc(), SILUndef::get(IL), *VarInfo);
+    }
+  }
 }
 
 void swift::salvageLoadDebugInfo(LoadOperation load) {

test/DebugInfo/salvage-integer-literal.swift

@@ -0,0 +1,13 @@
+// RUN: %target-swift-frontend -O -g -emit-sil %s | %FileCheck %s
+
+// In optimized code, a + b will be folded to 5, but we should still keep their
+// debug values.
+
+// CHECK-LABEL: sil
+public func f() -> Int {
+  let a = 2
+  let b = 3
+  // CHECK: debug_value undef : $Builtin.Int64, let, name "a", type $Int, expr op_constu:2:op_fragment:#Int._value
+  // CHECK: debug_value undef : $Builtin.Int64, let, name "b", type $Int, expr op_constu:3:op_fragment:#Int._value
+  return a + b
+}