IRGen: debug info generation for cond_fail messages.

To display a failure message in the debugger, create a function in the debug info which has the name of the failure message.
The debug location of the trap/cond_fail is then wrapped into this function and the function is declared as "inlined".
In case the debugger stops at the trap instruction, it displays the inline function, which looks like the failure message.
For example:

* thread #1, queue = 'com.apple.main-thread', stop reason = EXC_BAD_INSTRUCTION (code=EXC_I386_INVOP, subcode=0x0)
    frame #0: 0x0000000100000cbf a.out`testit3(_:) [inlined] Unexpectedly found nil while unwrapping an Optional value at test.swift:14:11 [opt]
   11
   12   @inline(never)
   13   func testit(_ a: Int?) -> Int {
-> 14     return a!
   15   }
   16

This change is currently not enabled by default, but can be enabled with the option "-Xllvm -enable-trap-debug-info".
Enabling this feature needs some changes in lldb. When the lldb part is done, this option can be removed and the feature enabled by default.

Author: eeckstein

lib/IRGen/GenBuiltin.cpp

@@ -204,7 +204,7 @@ void irgen::emitBuiltinCall(IRGenFunction &IGF, const BuiltinInfo &Builtin,
 
   // Emit non-mergeable traps only.
   if (IGF.Builder.isTrapIntrinsic(IID)) {
-    IGF.Builder.CreateNonMergeableTrap(IGF.IGM);
+    IGF.Builder.CreateNonMergeableTrap(IGF.IGM, StringRef());
     return;
   }
 
@@ -359,7 +359,8 @@ if (Builtin.ID == BuiltinValueKind::id) { \
     // string literal. If we ever get to the point of executing this builtin
     // at run time, it implies an incorrect use of the builtin and must result
     // in a trap.
-    IGF.emitTrap(/*Unreachable=*/false);
+    IGF.emitTrap("invalid use of globalStringTablePointer",
+                 /*Unreachable=*/false);
     auto returnValue = llvm::UndefValue::get(IGF.IGM.Int8PtrTy);
     // Consume the arguments of the builtin.
     (void)args.claimAll();

lib/IRGen/GenCast.cpp

@@ -469,7 +469,7 @@ emitExistentialScalarCastFn(IRGenModule &IGM,
   }
 
   case CheckedCastMode::Unconditional: {
-    IGF.emitTrap(/*EmitUnreachable=*/true);
+    IGF.emitTrap("type cast failed", /*EmitUnreachable=*/true);
     break;
   }
   }

lib/IRGen/IRBuilder.h

@@ -307,7 +307,7 @@ class IRBuilder : public IRBuilderBase {
   /// Call the trap intrinsic. If optimizations are enabled, an inline asm
   /// gadget is emitted before the trap. The gadget inhibits transforms which
   /// merge trap calls together, which makes debugging crashes easier.
-  llvm::CallInst *CreateNonMergeableTrap(IRGenModule &IGM);
+  llvm::CallInst *CreateNonMergeableTrap(IRGenModule &IGM, StringRef failureMsg);
 
   /// Split a first-class aggregate value into its component pieces.
   template <unsigned N>

lib/IRGen/IRGenDebugInfo.cpp

@@ -148,6 +148,9 @@ class IRGenDebugInfoImpl : public IRGenDebugInfo {
 
   void setCurrentLoc(IRBuilder &Builder, const SILDebugScope *DS,
                      SILLocation Loc);
+
+  void addFailureMessageToCurrentLoc(IRBuilder &Builder, StringRef failureMsg);
+
   void clearLoc(IRBuilder &Builder);
   void pushLoc();
   void popLoc();
@@ -1828,7 +1831,37 @@ void IRGenDebugInfoImpl::setCurrentLoc(IRBuilder &Builder,
   auto DL = llvm::DebugLoc::get(L.Line, L.Column, Scope, InlinedAt);
   Builder.SetCurrentDebugLocation(DL);
 }
+  
+void IRGenDebugInfoImpl::addFailureMessageToCurrentLoc(IRBuilder &Builder,
+                                                       StringRef failureMsg) {
+  auto TrapLoc = Builder.getCurrentDebugLocation();
+
+  // Create a function in the debug info which has failureMsg as name.
+  // TrapSc is the SIL debug scope which corresponds to TrapSP in the LLVM debug
+  // info.
+  RegularLocation ALoc = RegularLocation::getAutoGeneratedLocation();
+  const SILDebugScope *TrapSc = new (IGM.getSILModule()) SILDebugScope(ALoc);
+
+  llvm::DISubroutineType *DIFnTy = DBuilder.createSubroutineType(nullptr);
+
+  std::string FuncName = "Swift runtime failure: ";
+  FuncName += failureMsg;
+
+  llvm::DISubprogram *TrapSP = DBuilder.createFunction(
+     MainModule, StringRef(), FuncName, TrapLoc->getFile(), 0, DIFnTy, 0,
+     llvm::DINode::FlagArtificial, llvm::DISubprogram::SPFlagDefinition,
+     nullptr, nullptr, nullptr);
 
+  ScopeCache[TrapSc] = llvm::TrackingMDNodeRef(TrapSP);
+  LastScope = TrapSc;
+  
+  assert(parentScopesAreSane(TrapSc) && "parent scope sanity check failed");
+  
+  // Wrap the existing TrapLoc into the failure function.
+  auto DL = llvm::DebugLoc::get(0, 0, TrapSP, TrapLoc);
+  Builder.SetCurrentDebugLocation(DL);
+}
+  
 void IRGenDebugInfoImpl::clearLoc(IRBuilder &Builder) {
   LastDebugLoc = {};
   LastScope = nullptr;
@@ -2320,6 +2353,12 @@ void IRGenDebugInfo::setCurrentLoc(IRBuilder &Builder, const SILDebugScope *DS,
   static_cast<IRGenDebugInfoImpl *>(this)->setCurrentLoc(Builder, DS, Loc);
 }
 
+void IRGenDebugInfo::addFailureMessageToCurrentLoc(IRBuilder &Builder,
+                                                   StringRef failureMsg) {
+  static_cast<IRGenDebugInfoImpl *>(this)->
+    addFailureMessageToCurrentLoc(Builder, failureMsg);
+}
+
 void IRGenDebugInfo::clearLoc(IRBuilder &Builder) {
   static_cast<IRGenDebugInfoImpl *>(this)->clearLoc(Builder);
 }

lib/IRGen/IRGenDebugInfo.h

@@ -59,6 +59,12 @@ class IRGenDebugInfo {
   void setCurrentLoc(IRBuilder &Builder, const SILDebugScope *DS,
                      SILLocation Loc);
 
+  /// Replace the current debug location in \p Builder with the same location, but contained in an
+  /// inlined function which is named like \p failureMsg.
+  ///
+  /// This lets the debugger display the \p failureMsg as an inlined function frame.
+  void addFailureMessageToCurrentLoc(IRBuilder &Builder, StringRef failureMsg);
+
   void clearLoc(IRBuilder &Builder);
 
   /// Push the current debug location onto a stack and initialize the

lib/IRGen/IRGenFunction.cpp

@@ -31,6 +31,10 @@
 using namespace swift;
 using namespace irgen;
 
+static llvm::cl::opt<bool> EnableTrapDebugInfo(
+    "enable-trap-debug-info", llvm::cl::Hidden,
+    llvm::cl::desc("Generate failure-message functions in the debug info"));
+
 IRGenFunction::IRGenFunction(IRGenModule &IGM, llvm::Function *Fn,
                              OptimizationMode OptMode,
                              const SILDebugScope *DbgScope,
@@ -432,7 +436,8 @@ Address IRGenFunction::emitAddressAtOffset(llvm::Value *base, Offset offset,
   return Address(slotPtr, objectAlignment);
 }
 
-llvm::CallInst *IRBuilder::CreateNonMergeableTrap(IRGenModule &IGM) {
+llvm::CallInst *IRBuilder::CreateNonMergeableTrap(IRGenModule &IGM,
+                                                  StringRef failureMsg) {
   if (IGM.IRGen.Opts.shouldOptimize()) {
     // Emit unique side-effecting inline asm calls in order to eliminate
     // the possibility that an LLVM optimization or code generation pass
@@ -452,13 +457,16 @@ llvm::CallInst *IRBuilder::CreateNonMergeableTrap(IRGenModule &IGM) {
   // Emit the trap instruction.
   llvm::Function *trapIntrinsic =
       llvm::Intrinsic::getDeclaration(&IGM.Module, llvm::Intrinsic::ID::trap);
+  if (EnableTrapDebugInfo && IGM.DebugInfo && !failureMsg.empty()) {
+    IGM.DebugInfo->addFailureMessageToCurrentLoc(*this, failureMsg);
+  }
   auto Call = IRBuilderBase::CreateCall(trapIntrinsic, {});
   setCallingConvUsingCallee(Call);
   return Call;
 }
 
-void IRGenFunction::emitTrap(bool EmitUnreachable) {
-  Builder.CreateNonMergeableTrap(IGM);
+void IRGenFunction::emitTrap(StringRef failureMessage, bool EmitUnreachable) {
+  Builder.CreateNonMergeableTrap(IGM, failureMessage);
   if (EmitUnreachable)
     Builder.CreateUnreachable();
 }

lib/IRGen/IRGenFunction.h

@@ -287,7 +287,7 @@ class IRGenFunction {
   void setDereferenceableLoad(llvm::LoadInst *load, unsigned size);
 
   /// Emit a non-mergeable trap call, optionally followed by a terminator.
-  void emitTrap(bool EmitUnreachable);
+  void emitTrap(StringRef failureMessage, bool EmitUnreachable);
 
 private:
   llvm::Instruction *AllocaIP;

lib/IRGen/IRGenSIL.cpp

@@ -3880,7 +3880,7 @@ static bool hasReferenceSemantics(IRGenSILFunction &IGF,
 static llvm::Value *emitIsUnique(IRGenSILFunction &IGF, SILValue operand,
                                  SourceLoc loc) {
   if (!hasReferenceSemantics(IGF, operand->getType())) {
-    IGF.emitTrap(/*EmitUnreachable=*/false);
+    IGF.emitTrap("isUnique called for a non-reference", /*EmitUnreachable=*/false);
     return llvm::UndefValue::get(IGF.IGM.Int1Ty);
   }
 
@@ -4540,7 +4540,7 @@ static void emitTrapAndUndefValue(IRGenSILFunction &IGF,
   IGF.FailBBs.push_back(failBB);
 
   IGF.Builder.emitBlock(failBB);
-  IGF.emitTrap(/*EmitUnreachable=*/true);
+  IGF.emitTrap("mismatching type layouts", /*EmitUnreachable=*/true);
 
   llvm::BasicBlock *contBB = llvm::BasicBlock::Create(IGF.IGM.getLLVMContext());
   IGF.Builder.emitBlock(contBB);
@@ -5441,7 +5441,7 @@ void IRGenSILFunction::visitCondFailInst(swift::CondFailInst *i) {
     // debug location. This is because zero is not an artificial line location
     // in CodeView.
     IGM.DebugInfo->setInlinedTrapLocation(Builder, i->getDebugScope());
-  emitTrap(/*EmitUnreachable=*/true);
+  emitTrap(i->getMessage(), /*EmitUnreachable=*/true);
   Builder.emitBlock(contBB);
   FailBBs.push_back(failBB);
 }

test/DebugInfo/linetable-codeview.swift

@@ -1,4 +1,4 @@
-// RUN: %swiftc_driver %s -g -debug-info-format=codeview -emit-ir -o - | %FileCheck %s
+// RUN: %swiftc_driver %s -g -debug-info-format=codeview -Xllvm -enable-trap-debug-info -emit-ir -o - | %FileCheck %s
 func markUsed<T>(_ t: T) {}
 func arithmetic(_ a: Int64, _ b: Int64) {
   markUsed(a + b)             // line 4
@@ -78,7 +78,9 @@ func foo() {
 // CHECK-DAG: ![[DIV]] = !DILocation(line: 5, scope:
 // FIXME: The location of ``@llvm.trap`` should be in Integers.swift.gyb
 //        instead of being artificial.
-// CHECK-DAG: ![[INLINEDADD]] = !DILocation(line: 0, scope: !{{[0-9]+}}, inlinedAt: ![[ADD]]
+// CHECK: ![[INLINEDADD]] = !DILocation(line: 0, scope: ![[FAILURE_FUNC:[0-9]+]], inlinedAt: ![[INLINELOC:[0-9]+]]
+// CHECK-DAG: !{{.*}} = distinct !DISubprogram(linkageName: "Swift runtime failure: arithmetic overflow", scope: {{.*}}, flags: DIFlagArtificial, spFlags: DISPFlagDefinition, {{.*}})
+// CHECK-DAG: ![[INLINELOC]] = !DILocation(line: 0, scope: !{{[0-9]+}}, inlinedAt: ![[ADD]]
 
 // NOTE: These prologue instructions are given artificial line locations for
 //       LLDB, but for CodeView they should have the location of the function

test/IRGen/condfail_message.swift

@@ -0,0 +1,15 @@
+// RUN: %target-swift-frontend -primary-file %s -g -Xllvm -enable-trap-debug-info -emit-ir | %FileCheck %s
+// RUN: %target-swift-frontend -primary-file %s -g -Xllvm -enable-trap-debug-info -O -emit-ir | %FileCheck %s
+
+// CHECK-LABEL: define hidden swiftcc i8 @"$s16condfail_message6testitys4Int8VADF"(i8)
+// CHECK: call void @llvm.trap(), !dbg [[LOC:![0-9]+]]
+
+func testit(_ a: Int8) -> Int8 {
+  return a + 1
+}
+
+// CHECK: [[CALLER_LOC:![0-9]+]] = !DILocation(line: 8, column: 12, scope: !{{.*}})
+// CHECK: [[LOC]] = !DILocation(line: 0, scope: [[FAILURE_FUNC:![0-9]+]], inlinedAt: [[CALLER_LOC]])
+// CHECK: [[FAILURE_FUNC]] = distinct !DISubprogram(linkageName: "Swift runtime failure: arithmetic overflow", scope: {{.*}}, file: {{.*}}, type: [[FUNC_TYPE:![0-9]+]], flags: DIFlagArtificial, spFlags: DISPFlagDefinition, {{.*}})
+// CHECK: [[FUNC_TYPE]] = !DISubroutineType(types: null)
+