Fixed a long standing spiller bug that's exposed by Thumb:

The code sequence before the spiller is something like:
                 = tMOVrr
        %reg1117 = tMOVrr
        %reg1078 = tLSLri %reg1117, 2

The it starts spilling:
        %r0 = tRestore <fi#5>, 0
        %r1 = tRestore <fi#7>, 0
        %r1 = tMOVrr %r1<kill>
        tSpill %r1, <fi#5>, 0
        %reg1078 = tLSLri %reg1117, 2

It restores the value while processing the first tMOVrr. At this point, the
spiller remembers fi#5 is available in %r0. Next it processes the second move.
It restores the source before the move and spills the result afterwards. The
move becomes a noop and is deleted. However, a spill has been inserted and that
should invalidate reuse of %r0 for fi#5 and add reuse of %r1 for fi#5.
Therefore, %reg1117 (which is also assigned fi#5) should get %r1, not %r0.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@34039 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/lib/CodeGen/VirtRegMap.cpp b/lib/CodeGen/VirtRegMap.cpp
index 8fb26a95cee2fbd80adf4a37a9253d38495bc9f0..947ce0a5b2ead51296ed58090fee44f820cc12e2 100644 (file)
--- a/lib/CodeGen/VirtRegMap.cpp
+++ b/lib/CodeGen/VirtRegMap.cpp
@@ -923,19 +923,6 @@ void LocalSpiller::RewriteMBB(MachineBasicBlock &MBB, VirtRegMap &VRM) {
         DOUT << "Store:\t" << *next(MII);
         MI.getOperand(i).setReg(PhysReg);
 
-        // Check to see if this is a noop copy.  If so, eliminate the
-        // instruction before considering the dest reg to be changed.
-        {
-          unsigned Src, Dst;
-          if (TII->isMoveInstr(MI, Src, Dst) && Src == Dst) {
-            ++NumDCE;
-            DOUT << "Removing now-noop copy: " << MI;
-            MBB.erase(&MI);
-            VRM.RemoveFromFoldedVirtMap(&MI);
-            goto ProcessNextInst;
-          }
-        }
-        
         // If there is a dead store to this stack slot, nuke it now.
         MachineInstr *&LastStore = MaybeDeadStores[StackSlot];
         if (LastStore) {
@@ -953,6 +940,19 @@ void LocalSpiller::RewriteMBB(MachineBasicBlock &MBB, VirtRegMap &VRM) {
         Spills.ClobberPhysReg(PhysReg);
         Spills.addAvailable(StackSlot, PhysReg);
         ++NumStores;
+
+        // Check to see if this is a noop copy.  If so, eliminate the
+        // instruction before considering the dest reg to be changed.
+        {
+          unsigned Src, Dst;
+          if (TII->isMoveInstr(MI, Src, Dst) && Src == Dst) {
+            ++NumDCE;
+            DOUT << "Removing now-noop copy: " << MI;
+            MBB.erase(&MI);
+            VRM.RemoveFromFoldedVirtMap(&MI);
+            goto ProcessNextInst;
+          }
+        }        
       }
     }
   ProcessNextInst: