Skip 32 bit relocation addend partitioning in MCCAS.

Relocations addednds do not deduplicate, to improve deduplication in
MCCAS, we store those addends in an AddendsRef block. This is much more
complicated to do in 32 bit architectures because of various corner
cases and complexities with the MachO 32-bit relocation format
Therefore we skip relocation partitioning for 32-bit architectures in
MCCAS.

Author: rastogishubham

llvm/lib/MCCAS/MCCASObjectV1.cpp

@@ -2445,6 +2445,15 @@ Error MCCASBuilder::buildFragments() {
         continue;
 
       SmallVector<char, 0> FinalFragmentContents;
+      // Set the RelocationBuffer to be an empty ArrayRef, and the
+      // RelocationBufferIndex to zero if the architecture is 32-bit, because we
+      // do not support relocation partitioning on 32-bit platforms. With this,
+      // partitionFragment will put all the fragment contents in the
+      // FinalFragmentContents, and the Addends buffer will be empty.
+      if (ObjectWriter.getAddressSize() == 4) {
+        RelocationBuffer = ArrayRef<MachO::any_relocation_info>();
+        RelocationBufferIndex = 0;
+      }
       partitionFragment(Layout, Addends, FinalFragmentContents,
                         RelocationBuffer, F, RelocationBufferIndex,
                         ObjectWriter.Target.isLittleEndian());
@@ -2846,25 +2855,32 @@ MCCASReader::reconstructSection(SmallVectorImpl<char> &SectionBuffer,
   /// copied the addend out of the Addends at a particular offset, we should
   /// skip all relocations that matches the same offset.
   int64_t PrevOffset = -1;
-  for (auto Reloc : Relocations.back()) {
-    auto RelocationOffsetInSection = getRelocationOffset(Reloc);
-    if (PrevOffset == RelocationOffsetInSection)
-      continue;
-    auto RelocationSize =
-        getRelocationSize(Reloc, getEndian() == endianness::little);
-    /// NumOfBytesToReloc: This denotes the number of bytes needed to be copied
-    /// into the \p SectionBuffer before we copy the next addend.
-    auto NumOfBytesToReloc = RelocationOffsetInSection - SectionBuffer.size();
-    // Copy the contents of the fragment till the next relocation.
-    SectionBuffer.append(FragmentBuffer.begin() + FragmentIndex,
-                         FragmentBuffer.begin() + FragmentIndex +
-                             NumOfBytesToReloc);
-    FragmentIndex += NumOfBytesToReloc;
-    // Copy the relocation addend.
-    SectionBuffer.append(Addends.begin() + AddendBufferIndex,
-                         Addends.begin() + AddendBufferIndex + RelocationSize);
-    AddendBufferIndex += RelocationSize;
-    PrevOffset = RelocationOffsetInSection;
+  /// If the \p Addends buffer is empty, there was no AddendsRef for this
+  /// section, this is either because no \p Relocations exist in this section,
+  /// or this is 32-bit architecture, where we do not support relocation
+  /// partitioning.
+  if (!Addends.empty()) {
+    for (auto Reloc : Relocations.back()) {
+      auto RelocationOffsetInSection = getRelocationOffset(Reloc);
+      if (PrevOffset == RelocationOffsetInSection)
+        continue;
+      auto RelocationSize =
+          getRelocationSize(Reloc, getEndian() == endianness::little);
+      /// NumOfBytesToReloc: This denotes the number of bytes needed to be
+      /// copied into the \p SectionBuffer before we copy the next addend.
+      auto NumOfBytesToReloc = RelocationOffsetInSection - SectionBuffer.size();
+      // Copy the contents of the fragment till the next relocation.
+      SectionBuffer.append(FragmentBuffer.begin() + FragmentIndex,
+                           FragmentBuffer.begin() + FragmentIndex +
+                               NumOfBytesToReloc);
+      FragmentIndex += NumOfBytesToReloc;
+      // Copy the relocation addend.
+      SectionBuffer.append(Addends.begin() + AddendBufferIndex,
+                           Addends.begin() + AddendBufferIndex +
+                               RelocationSize);
+      AddendBufferIndex += RelocationSize;
+      PrevOffset = RelocationOffsetInSection;
+    }
   }
   // Copy any remaining bytes of the fragment into the SectionBuffer.
   SectionBuffer.append(FragmentBuffer.begin() + FragmentIndex,

llvm/test/CAS/test-reloc-mccas-32bit-arm.s

@@ -0,0 +1,9 @@
+# This test tests to make sure mccas can handle scattered relocations properly on 32 bit arm
+
+# RUN: rm -rf %t && mkdir -p %t
+# RUN: llvm-mc --cas=%t/cas --cas-backend --mccas-verify -triple=armv7-apple-darwin10  -filetype=obj -o %t/reloc.o %s
+
+    movw  r0, :lower16:(fn2-L1)
+L1:
+fn2:
+

llvm/test/CAS/test-reloc-mccas-32bit.s

@@ -0,0 +1,6 @@
+# This test tests to make sure mccas can handle scattered relocations properly on 32 bit x86
+
+# RUN: rm -rf %t && mkdir -p %t
+# RUN: llvm-mc --cas=%t/cas --cas-backend --mccas-verify  -triple=i386-apple-macosx10.4 -filetype=obj -o %t/reloc.o %s
+        movl    y+4, %ecx
+.zerofill __DATA,__common,y,8,3