[TableGen] Fix SubRegIndex size computation for concatenated subregs of unknown size

When calculating the size of concatenated subregisters, and at least
one of the subregisters involved has an unknown size (-1), then the
concatenated size should be set to -1 as well.

This bug was found for an out-of-tree target.

Looking at lib/Target the only in-tree target that has a subregister
with unknown size is X86:
  X86RegisterInfo.td:  def sub_mask_0   : SubRegIndex<-1>;

But it looks like sub_mask_0 don't result in any concatenated subreg
index with faulty size if looking at X86SubRegIdxRanges[].

Differential Revision: https://reviews.llvm.org/D138341

1 files changed, 6 insertions, 2 deletions

diff --git a/llvm/utils/TableGen/CodeGenRegisters.cpp b/llvm/utils/TableGen/CodeGenRegisters.cpp
index 999c720..5454126 100644
--- a/llvm/utils/TableGen/CodeGenRegisters.cpp
+++ b/llvm/utils/TableGen/CodeGenRegisters.cpp
@@ -1369,11 +1369,15 @@ getConcatSubRegIndex(const SmallVector<CodeGenSubRegIndex *, 8> &Parts) {
   unsigned Size = Parts.front()->Size;
   unsigned LastOffset = Parts.front()->Offset;
   unsigned LastSize = Parts.front()->Size;
+  unsigned UnknownSize = (uint16_t)-1;
   for (unsigned i = 1, e = Parts.size(); i != e; ++i) {
     Name += '_';
     Name += Parts[i]->getName();
-    Size += Parts[i]->Size;
-    if (Parts[i]->Offset != (LastOffset + LastSize))
+    if (Size == UnknownSize || Parts[i]->Size == UnknownSize)
+      Size = UnknownSize;
+    else
+      Size += Parts[i]->Size;
+    if (LastSize == UnknownSize || Parts[i]->Offset != (LastOffset + LastSize))
       isContinuous = false;
     LastOffset = Parts[i]->Offset;
     LastSize = Parts[i]->Size;