Merge pull request swiftlang#18447 from sparkasaurusRex/codeview-linetables

Reduce breaks in CodeView linetables

Author: dcci

include/swift/SIL/SILLocation.h

@@ -295,6 +295,11 @@ class SILLocation {
   /// contain calls, which the debugger could be able to step into.
   bool isAutoGenerated() const { return KindData & (1 << AutoGeneratedBit); }
 
+  /// Returns true if the line number of this location is zero.
+  bool isLineZero(const SourceManager &SM) const {
+    return decodeDebugLoc(SM).Line == 0;
+  }
+
   /// Changes the default source location position to point to start of
   /// the AST node.
   void pointToStart() { KindData |= (1 << PointsToStartBit); }

lib/IRGen/IRGenDebugInfo.cpp

@@ -1575,6 +1575,9 @@ void IRGenDebugInfoImpl::setCurrentLoc(IRBuilder &Builder,
   if (!Scope)
     return;
 
+  // NOTE: In CodeView, zero is not an artificial line location. We try to
+  //       avoid those line locations near user code to reduce the number
+  //       of breaks in the linetables.
   SILLocation::DebugLoc L;
   SILFunction *Fn = DS->getInlinedFunction();
   if (Fn && (Fn->isThunk() || Fn->isTransparent())) {
@@ -1583,10 +1586,11 @@ void IRGenDebugInfoImpl::setCurrentLoc(IRBuilder &Builder,
     // Reuse the last source location if we are still in the same
     // scope to get a more contiguous line table.
     L = LastDebugLoc;
-  } else if (DS == LastScope && Loc.is<ArtificialUnreachableLocation>() &&
+  } else if (DS == LastScope &&
+             (Loc.is<ArtificialUnreachableLocation>() || Loc.isLineZero(SM)) &&
              Opts.DebugInfoFormat == IRGenDebugInfoFormat::CodeView) {
-    // Remove unreachable locations with line zero because line zero does not
-    // represent an artificial location in CodeView.
+    // If the scope has not changed and the line number is either zero or
+    // artificial, we want to keep the most recent debug location.
     L = LastDebugLoc;
   } else {
     // Decode the location.

test/DebugInfo/columns.swift

@@ -24,7 +24,6 @@ public func foo(_ a: Int64, _ b: Int64) -> Int64 {      // line 5
 
 // CV-CHECK-DAG: !DILexicalBlock({{.*}}, line: 5)
 // CV-CHECK-DAG: ![[DIV]] = !DILocation(line: 8, scope:
-// CV-CHECK-DAG: ![[ADD]] = !DILocation(line: 8, scope:
 // CV-CHECK-DAG: ![[SLT]] = !DILocation(line: 10, scope:
 // CV-CHECK-DAG: !DILexicalBlock({{.*}}, line: 10)
 // CV-CHECK-DAG: ![[SUB]] = !DILocation(line: 12, scope:

test/DebugInfo/linetable-codeview.swift

@@ -25,6 +25,9 @@ func mySwitch(_ a: Int64) {
     }                         // line 25
   }
 }
+func foo() {
+  var myArray: [Int64] = []   // line 29
+}
 
 // func arithmetic(_ a: Int64, _ b: Int64)
   // CHECK: define {{.*}} @"$S4main10arithmeticyys5Int64V_ADtF"(i64, i64)
@@ -62,6 +65,14 @@ func mySwitch(_ a: Int64) {
   // CHECK: ; <label>:[[RETLABEL]]:
   // CHECK-NEXT: ret void
 
+// func foo()
+  // CHECK: define {{.*}} @"$S4main3fooyyF"
+  // CHECK: %[[MYARRAY:.*]] = alloca
+  // CHECK: call void @llvm.dbg.declare(metadata %TSa* %[[MYARRAY]],
+  // CHECK-SAME: !dbg ![[ARRAY:[0-9]+]]
+  // CHECK: call swiftcc { {{.*}} } @"${{.*}}_allocateUninitializedArray{{.*}}"
+  // CHECK-SAME: !dbg ![[ARRAY]]
+  // CHECK: ret void
 
 // CHECK-DAG: ![[ADD]] = !DILocation(line: 4, scope:
 // CHECK-DAG: ![[DIV]] = !DILocation(line: 5, scope:
@@ -78,3 +89,4 @@ func mySwitch(_ a: Int64) {
 // CHECK-DAG: ![[FORBODY]] = !DILocation(line: 16, scope:
 // CHECK-DAG: ![[CASE]] = !DILocation(line: 22, scope:
 // CHECK-DAG: ![[DEFAULTCLEANUP]] = !DILocation(line: 25, scope:
+// CHECK-DAG: ![[ARRAY]] = !DILocation(line: 29, scope: