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

3 files changed, 7 insertions, 3 deletions

diff --git a/lib/Target/ARM/ARMAsmPrinter.cpp b/lib/Target/ARM/ARMAsmPrinter.cpp
index eca6039abf..6d37416d0c 100644
--- a/lib/Target/ARM/ARMAsmPrinter.cpp
+++ b/lib/Target/ARM/ARMAsmPrinter.cpp
@@ -1481,11 +1481,10 @@ void ARMAsmPrinter::EmitInstruction(const MachineInstr *MI) {
     /// in the function.  The first operand is the ID# for this instruction, the
     /// second is the index into the MachineConstantPool that this is, the third
     /// is the size in bytes of this constant pool entry.
+    /// The required alignment is specified on the basic block holding this MI.
     unsigned LabelId = (unsigned)MI->getOperand(0).getImm();
     unsigned CPIdx   = (unsigned)MI->getOperand(1).getIndex();
 
-    EmitAlignment(2);
-
     // Mark the constant pool entry as data if we're not already in a data
     // region.
     OutStreamer.EmitDataRegion();
diff --git a/lib/Target/ARM/ARMConstantIslandPass.cpp b/lib/Target/ARM/ARMConstantIslandPass.cpp
index fedbbad56f..017e908206 100644
--- a/lib/Target/ARM/ARMConstantIslandPass.cpp
+++ b/lib/Target/ARM/ARMConstantIslandPass.cpp
@@ -398,6 +398,9 @@ void ARMConstantIslands::DoInitialPlacement(MachineFunction &MF,
   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 @@ bool ARMConstantIslands::HandleConstantPoolUser(MachineFunction &MF,
   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))
diff --git a/test/CodeGen/ARM/globals.ll b/test/CodeGen/ARM/globals.ll
index 5e7e3f2a92..eb71149d83 100644
--- a/test/CodeGen/ARM/globals.ll
+++ b/test/CodeGen/ARM/globals.ll
@@ -70,6 +70,5 @@ define i32 @test1() {
 ; LinuxPIC: .align 2
 ; LinuxPIC: .LCPI0_0:
 ; LinuxPIC:     .long _GLOBAL_OFFSET_TABLE_-(.LPC0_0+8)
-; LinuxPIC: .align 2
 ; LinuxPIC: .LCPI0_1:
 ; LinuxPIC:     .long	G(GOT)