[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, 18 insertions, 7 deletions

diff --git a/llvm/lib/Bitcode/Reader/MetadataLoader.cpp b/llvm/lib/Bitcode/Reader/MetadataLoader.cpp
index 7d79956a811..5250ac5176d 100644
--- a/llvm/lib/Bitcode/Reader/MetadataLoader.cpp
+++ b/llvm/lib/Bitcode/Reader/MetadataLoader.cpp
@@ -1174,14 +1174,25 @@ Error MetadataLoader::MetadataLoaderImpl::parseOneMetadata(
     break;
   }
   case bitc::METADATA_SUBRANGE: {
-    if (Record.size() != 3)
-      return error("Invalid record");
+    Metadata *Val = nullptr;
+    // Operand 'count' is interpreted as:
+    // - Signed integer (version 0)
+    // - Metadata node  (version 1)
+    switch (Record[0] >> 1) {
+    case 0:
+      Val = GET_OR_DISTINCT(DISubrange,
+                            (Context, Record[1], unrotateSign(Record.back())));
+      break;
+    case 1:
+      Val = GET_OR_DISTINCT(DISubrange, (Context, getMDOrNull(Record[1]),
+                                         unrotateSign(Record.back())));
+      break;
+    default:
+      return error("Invalid record: Unsupported version of DISubrange");
+    }
 
-    IsDistinct = Record[0];
-    MetadataList.assignValue(
-        GET_OR_DISTINCT(DISubrange,
-                        (Context, Record[1], unrotateSign(Record[2]))),
-        NextMetadataNo);
+    MetadataList.assignValue(Val, NextMetadataNo);
+    IsDistinct = Record[0] & 1;
     NextMetadataNo++;
     break;
   }