Fix a bug in the Thumb1 ARM Load/Store optimizer

Previously, the basic block was searched for future uses of the base register,
and if necessary any writeback to the base register was reset using a SUB
instruction (e.g. before calling a function) just before such a use. However,
this step happened *before* the merged LDM/STM instruction was built. So if
there was (e.g.) a function call directly after the not-yet-formed LDM/STM,
the pass would first insert a SUB instruction to reset the base register,
and then (at the same location, incorrectly) insert the LDM/STM itself.

This patch fixes PR19972. Patch by Moritz Roth.

llvm-svn: 210542

1 files changed, 7 insertions, 7 deletions

diff --git a/llvm/lib/Target/ARM/ARMLoadStoreOptimizer.cpp b/llvm/lib/Target/ARM/ARMLoadStoreOptimizer.cpp
index ee7df54..62fd059 100644
--- a/llvm/lib/Target/ARM/ARMLoadStoreOptimizer.cpp
+++ b/llvm/lib/Target/ARM/ARMLoadStoreOptimizer.cpp
@@ -505,7 +505,7 @@ ARMLoadStoreOpt::MergeOps(MachineBasicBlock &MBB,
 
   // Exception: If the base register is in the input reglist, Thumb1 LDM is
   // non-writeback. Check for this.
-  if (Opcode == ARM::tLDRi && isThumb1)
+  if (Opcode == ARM::tLDMIA && isThumb1)
     for (unsigned I = 0; I < NumRegs; ++I)
       if (Base == Regs[I].first) {
         Writeback = false;
@@ -519,17 +519,17 @@ ARMLoadStoreOpt::MergeOps(MachineBasicBlock &MBB,
       // Update tLDMIA with writeback if necessary.
       Opcode = ARM::tLDMIA_UPD;
 
-    // The base isn't dead after a merged instruction with writeback. Update
-    // future uses of the base with the added offset (if possible), or reset
-    // the base register as necessary.
-    if (!BaseKill)
-      UpdateBaseRegUses(MBB, MBBI, dl, Base, NumRegs, Pred, PredReg);
-
     MIB = BuildMI(MBB, MBBI, dl, TII->get(Opcode));
 
     // Thumb1: we might need to set base writeback when building the MI.
     MIB.addReg(Base, getDefRegState(true))
        .addReg(Base, getKillRegState(BaseKill));
+
+    // The base isn't dead after a merged instruction with writeback. Update
+    // future uses of the base with the added offset (if possible), or reset
+    // the base register as necessary.
+    if (!BaseKill)
+      UpdateBaseRegUses(MBB, MBBI, dl, Base, NumRegs, Pred, PredReg);
   } else {
     // No writeback, simply build the MachineInstr.
     MIB = BuildMI(MBB, MBBI, dl, TII->get(Opcode));