Align ARM constant pool islands via their basic block.

Previously, all ARM::CONSTPOOL_ENTRY instructions had a hardwired
alignment of 4 bytes emitted by ARMAsmPrinter.  Now the same alignment
is set on the basic block.

This is in preparation of supporting ARM constant pool islands with
different alignments.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@145890 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Target/ARM/ARMConstantIslandPass.cpp b/lib/Target/ARM/ARMConstantIslandPass.cpp
index fedbbad..017e908 100644
--- a/lib/Target/ARM/ARMConstantIslandPass.cpp
+++ b/lib/Target/ARM/ARMConstantIslandPass.cpp
@@ -398,6 +398,9 @@
   MachineBasicBlock *BB = MF.CreateMachineBasicBlock();
   MF.push_back(BB);
 
+  // Mark the basic block as 4-byte aligned as required by the const-pool.
+  BB->setAlignment(2);
+
   // Add all of the constants from the constant pool to the end block, use an
   // identity mapping of CPI's to CPE's.
   const std::vector<MachineConstantPoolEntry> &CPs =
@@ -1311,6 +1314,9 @@
   CPEntries[CPI].push_back(CPEntry(U.CPEMI, ID, 1));
   ++NumCPEs;
 
+  // Mark the basic block as 4-byte aligned as required by the const-pool entry.
+  NewIsland->setAlignment(2);
+
   BBOffsets[NewIsland->getNumber()] = BBOffsets[NewMBB->getNumber()];
   // Compensate for .align 2 in thumb mode.
   if (isThumb && (BBOffsets[NewIsland->getNumber()]%4 != 0 || HasInlineAsm))