[DebugInfo] Enable debug information for C99 VLA types

Summary:
This patch enables debugging of C99 VLA types by generating more precise
LLVM Debug metadata, using the extended DISubrange 'count' field that
takes a DIVariable.
    
This should implement:
  Bug 30553: Debug info generated for arrays is not what GDB expects (not as good as GCC's)
https://bugs.llvm.org/show_bug.cgi?id=30553

Reviewers: echristo, aprantl, dexonsmith, clayborg, pcc, kristof.beyls, dblaikie

Reviewed By: aprantl

Subscribers: jholewinski, schweitz, davide, fhahn, JDevlieghere, cfe-commits

Differential Revision: https://reviews.llvm.org/D41698

llvm-svn: 323952

1 files changed, 22 insertions, 11 deletions

diff --git a/clang/lib/CodeGen/CodeGenFunction.cpp b/clang/lib/CodeGen/CodeGenFunction.cpp
index e62d3e75b71..a7591b10455 100644
--- a/clang/lib/CodeGen/CodeGenFunction.cpp
+++ b/clang/lib/CodeGen/CodeGenFunction.cpp
@@ -1758,12 +1758,9 @@ CodeGenFunction::EmitNullInitialization(Address DestPtr, QualType Ty) {
     if (const VariableArrayType *vlaType =
           dyn_cast_or_null<VariableArrayType>(
                                           getContext().getAsArrayType(Ty))) {
-      QualType eltType;
-      llvm::Value *numElts;
-      std::tie(numElts, eltType) = getVLASize(vlaType);
-
-      SizeVal = numElts;
-      CharUnits eltSize = getContext().getTypeSizeInChars(eltType);
+      auto VlaSize = getVLASize(vlaType);
+      SizeVal = VlaSize.NumElts;
+      CharUnits eltSize = getContext().getTypeSizeInChars(VlaSize.Type);
       if (!eltSize.isOne())
         SizeVal = Builder.CreateNUWMul(SizeVal, CGM.getSize(eltSize));
       vla = vlaType;
@@ -1846,7 +1843,7 @@ llvm::Value *CodeGenFunction::emitArrayLength(const ArrayType *origArrayType,
   // this is the size of the VLA in bytes, not its size in elements.
   llvm::Value *numVLAElements = nullptr;
   if (isa<VariableArrayType>(arrayType)) {
-    numVLAElements = getVLASize(cast<VariableArrayType>(arrayType)).first;
+    numVLAElements = getVLASize(cast<VariableArrayType>(arrayType)).NumElts;
 
     // Walk into all VLAs.  This doesn't require changes to addr,
     // which has type T* where T is the first non-VLA element type.
@@ -1927,14 +1924,13 @@ llvm::Value *CodeGenFunction::emitArrayLength(const ArrayType *origArrayType,
   return numElements;
 }
 
-std::pair<llvm::Value*, QualType>
-CodeGenFunction::getVLASize(QualType type) {
+CodeGenFunction::VlaSizePair CodeGenFunction::getVLASize(QualType type) {
   const VariableArrayType *vla = getContext().getAsVariableArrayType(type);
   assert(vla && "type was not a variable array type!");
   return getVLASize(vla);
 }
 
-std::pair<llvm::Value*, QualType>
+CodeGenFunction::VlaSizePair
 CodeGenFunction::getVLASize(const VariableArrayType *type) {
   // The number of elements so far; always size_t.
   llvm::Value *numElements = nullptr;
@@ -1955,7 +1951,22 @@ CodeGenFunction::getVLASize(const VariableArrayType *type) {
     }
   } while ((type = getContext().getAsVariableArrayType(elementType)));
 
-  return std::pair<llvm::Value*,QualType>(numElements, elementType);
+  return { numElements, elementType };
+}
+
+CodeGenFunction::VlaSizePair
+CodeGenFunction::getVLAElements1D(QualType type) {
+  const VariableArrayType *vla = getContext().getAsVariableArrayType(type);
+  assert(vla && "type was not a variable array type!");
+  return getVLAElements1D(vla);
+}
+
+CodeGenFunction::VlaSizePair
+CodeGenFunction::getVLAElements1D(const VariableArrayType *Vla) {
+  llvm::Value *VlaSize = VLASizeMap[Vla->getSizeExpr()];
+  assert(VlaSize && "no size for VLA!");
+  assert(VlaSize->getType() == SizeTy);
+  return { VlaSize, Vla->getElementType() };
 }
 
 void CodeGenFunction::EmitVariablyModifiedType(QualType type) {