[llvm-commits] CVS: llvm/lib/CodeGen/VirtRegMap.cpp

[Evan Cheng]

Changes in directory llvm/lib/CodeGen:

VirtRegMap.cpp updated: 1.94 -> 1.95
---
Log message:

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.


---
Diffs of the changes:  (+13 -13)

 VirtRegMap.cpp |   26 +++++++++++++-------------
 1 files changed, 13 insertions(+), 13 deletions(-)


Index: llvm/lib/CodeGen/VirtRegMap.cpp
diff -u llvm/lib/CodeGen/VirtRegMap.cpp:1.94 llvm/lib/CodeGen/VirtRegMap.cpp:1.95
--- llvm/lib/CodeGen/VirtRegMap.cpp:1.94	Mon Jan 22 18:59:48 2007
+++ llvm/lib/CodeGen/VirtRegMap.cpp	Thu Feb  8 00:04:54 2007
@@ -923,19 +923,6 @@
         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 @@
         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: