When generating debug info for AllocStackInst, make sure to describe the alloca.

This way an llvm.dbg.declare instrinsic is used, which is valid for
the entire lifetime of the alloca.

rdar://problem/36663932

Author: adrian-prantl

lib/IRGen/IRGenSIL.cpp

@@ -3885,6 +3885,11 @@ void IRGenSILFunction::emitDebugInfoForAllocStack(AllocStackInst *i,
         RealType, type, false);
     bool IsAnonymous = false;
     StringRef Name = getVarName(i, IsAnonymous);
+    // Describe the underlying alloca. This way an llvm.dbg.declare instrinsic
+    // is used, which is valid for the entire lifetime of the alloca.
+    if (auto *BitCast = dyn_cast<llvm::BitCastInst>(addr))
+      if (auto *Alloca = dyn_cast<llvm::AllocaInst>(BitCast->getOperand(0)))
+        addr = Alloca;
     if (auto DS = i->getDebugScope())
       emitDebugVariableDeclaration(addr, DbgTy, SILTy, DS, Decl, Name,
                                    i->getVarInfo().ArgNo);

test/DebugInfo/generic_enum_closure.swift

@@ -8,7 +8,8 @@ struct CErrorOr<T>
     // CHECK: define hidden {{.*}}void @"$S20generic_enum_closure8CErrorOrV1xACyxGAA14__CurrentErrnoV_tcfC"
     // CHECK-NOT: define
     // This is a SIL-level debug_value_addr instruction.
-    // CHECK: call void @llvm.dbg.value({{.*}}, metadata ![[SELF:.*]], metadata !DIExpression())
+    // CHECK: call void @llvm.dbg.declare
+    // CHECK: call void @llvm.dbg.declare({{.*}}, metadata ![[SELF:.*]], metadata !DIExpression())
     // CHECK: ![[T1:.*]] = !DICompositeType({{.*}}, identifier: "$S20generic_enum_closure8CErrorOrVyACQq_GD")
     // CHECK: ![[SELF]] = !DILocalVariable(name: "self", scope: {{.*}}, type: ![[T1]])
     value = .none

test/DebugInfo/resilience.swift

@@ -0,0 +1,23 @@
+// RUN: %empty-directory(%t)
+// RUN: %target-swift-frontend -g -emit-module -enable-resilience \
+// RUN:   -emit-module-path=%t/resilient_struct.swiftmodule \
+// RUN:   -module-name=resilient_struct %S/../Inputs/resilient_struct.swift
+// RUN: %target-swift-frontend -g -I %t -emit-ir -enable-resilience %s \
+// RUN:   | %FileCheck %s
+import resilient_struct
+
+func use<T>(_ t: T) {}
+
+public func f() {
+  let s1 = Size(w: 1, h: 2)
+  use(s1)
+  // CHECK: %[[USE_BUFFER:.*]] = alloca i8,
+  // CHECK: %[[S1:.*]] = alloca i8,
+  // CHECK: call void @llvm.dbg.declare(metadata i8* %[[S1]],
+  // CHECK-SAME:                        metadata ![[V1:[0-9]+]],
+  // CHECK-SAME:                        metadata !DIExpression())
+  // CHECK: ![[V1]] = !DILocalVariable(name: "s1", {{.*}}type: ![[TY:[0-9]+]])
+  // CHECK: ![[TY]] = !DICompositeType(tag: DW_TAG_structure_type, name: "Size",
+  // FIXME-NOT: size:
+  // CHECK: =
+}