Thumb2 size reduction fix for tied operands of tMUL.

The tied source operand of tMUL is the second source operand, not the
first like every other two-address thumb instruction. Special case it
in the size reduction pass to make sure we create the tMUL instruction
properly.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@151315 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 13 insertions, 1 deletions

diff --git a/lib/Target/ARM/Thumb2SizeReduction.cpp b/lib/Target/ARM/Thumb2SizeReduction.cpp
index 4abff28f02..776d0eff5e 100644
--- a/lib/Target/ARM/Thumb2SizeReduction.cpp
+++ b/lib/Target/ARM/Thumb2SizeReduction.cpp
@@ -597,7 +597,19 @@ Thumb2SizeReduce::ReduceTo2Addr(MachineBasicBlock &MBB, MachineInstr *MI,
 
   unsigned Reg0 = MI->getOperand(0).getReg();
   unsigned Reg1 = MI->getOperand(1).getReg();
-  if (Reg0 != Reg1) {
+  // t2MUL is "special". The tied source operand is second, not first.
+  if (MI->getOpcode() == ARM::t2MUL) {
+    if (Reg0 != MI->getOperand(2).getReg()) {
+      // If the other operand also isn't the same as the destination, we
+      // can't reduce.
+      if (Reg1 != Reg0)
+        return false;
+      // Try to commute the operands to make it a 2-address instruction.
+      MachineInstr *CommutedMI = TII->commuteInstruction(MI);
+      if (!CommutedMI)
+        return false;
+    }
+  } else if (Reg0 != Reg1) {
     // Try to commute the operands to make it a 2-address instruction.
     unsigned CommOpIdx1, CommOpIdx2;
     if (!TII->findCommutedOpIndices(MI, CommOpIdx1, CommOpIdx2) ||