[Metadata] Extend 'count' field of DISubrange to take a metadata node

Summary:
This patch extends the DISubrange 'count' field to take either a
(signed) constant integer value or a reference to a DILocalVariable
or DIGlobalVariable.

This is patch [1/3] in a series to extend LLVM's DISubrange Metadata
node to support debugging of C99 variable length arrays and vectors with
runtime length like the Scalable Vector Extension for AArch64. It is
also a first step towards representing more complex cases like arrays
in Fortran.

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

Reviewed By: aprantl

Subscribers: rnk, probinson, fhahn, aemerson, rengolin, JDevlieghere, llvm-commits

Differential Revision: https://reviews.llvm.org/D41695

llvm-svn: 323313

1 files changed, 3 insertions, 1 deletions

diff --git a/llvm/lib/CodeGen/AsmPrinter/CodeViewDebug.cpp b/llvm/lib/CodeGen/AsmPrinter/CodeViewDebug.cpp
index 11c28ba..bee4d11 100644
--- a/llvm/lib/CodeGen/AsmPrinter/CodeViewDebug.cpp
+++ b/llvm/lib/CodeGen/AsmPrinter/CodeViewDebug.cpp
@@ -1325,7 +1325,9 @@ TypeIndex CodeViewDebug::lowerTypeArray(const DICompositeType *Ty) {
     const DISubrange *Subrange = cast<DISubrange>(Element);
     assert(Subrange->getLowerBound() == 0 &&
            "codeview doesn't support subranges with lower bounds");
-    int64_t Count = Subrange->getCount();
+    int64_t Count = -1;
+    if (auto *CI = Subrange->getCount().dyn_cast<ConstantInt*>())
+      Count = CI->getSExtValue();
 
     // Forward declarations of arrays without a size and VLAs use a count of -1.
     // Emit a count of zero in these cases to match what MSVC does for arrays