[ARM] More care with Thumb1 writeback in ARMLoadStoreOptimizer

Differential Revision: http://reviews.llvm.org/D13240

llvm-svn: 249002

1 files changed, 7 insertions, 3 deletions

diff --git a/llvm/lib/Target/ARM/ARMLoadStoreOptimizer.cpp b/llvm/lib/Target/ARM/ARMLoadStoreOptimizer.cpp
index d099deda26c..d0cd9efc29a 100644
--- a/llvm/lib/Target/ARM/ARMLoadStoreOptimizer.cpp
+++ b/llvm/lib/Target/ARM/ARMLoadStoreOptimizer.cpp
@@ -630,9 +630,10 @@ MachineInstr *ARMLoadStoreOpt::CreateLoadStoreMulti(MachineBasicBlock &MBB,
 
     unsigned NewBase;
     if (isi32Load(Opcode)) {
-      // If it is a load, then just use one of the destination register to
-      // use as the new base.
+      // If it is a load, then just use one of the destination registers
+      // as the new base. Will no longer be writeback in Thumb1.
       NewBase = Regs[NumRegs-1].first;
+      Writeback = false;
     } else {
       // Find a free register that we can use as scratch register.
       moveLiveRegsBefore(MBB, InsertBefore);
@@ -736,9 +737,12 @@ MachineInstr *ARMLoadStoreOpt::CreateLoadStoreMulti(MachineBasicBlock &MBB,
   MachineInstrBuilder MIB;
 
   if (Writeback) {
-    if (Opcode == ARM::tLDMIA)
+    assert(isThumb1 && "expected Writeback only inThumb1");
+    if (Opcode == ARM::tLDMIA) {
+      assert(!(ContainsReg(Regs, Base)) && "Thumb1 can't LDM ! with Base in Regs");
       // Update tLDMIA with writeback if necessary.
       Opcode = ARM::tLDMIA_UPD;
+    }
 
     MIB = BuildMI(MBB, InsertBefore, DL, TII->get(Opcode));