[llvm-commits] [llvm] r136973 - /llvm/trunk/lib/CodeGen/BranchFolding.cpp

[Jakob Stoklund Olesen]

Author: stoklund
Date: Fri Aug  5 13:47:07 2011
New Revision: 136973

URL: http://llvm.org/viewvc/llvm-project?rev=136973&view=rev
Log:
Fix liveness computations in BranchFolding.

The old code would look at kills and defs in one pass over the
instruction operands, causing problems with this code:

  %R0<def>, %CPSR<def,dead> = tLSLri %R5<kill>, 2, pred:14, pred:%noreg
  %R0<def>, %CPSR<def,dead> = tADDrr %R4<kill>, %R0<kill>, pred:14, %pred:%noreg

The last instruction kills and redefines %R0, so it is still live after
the instruction.

This caused a register scavenger crash when compiling 483.xalancbmk for
armv6. I am not including a test case because it requires too much bad
luck to expose this old bug.

First you need to convince the register allocator to use %R0 twice on
the tADDrr instruction, then you have to convince BranchFolding to do
something that causes it to run the register scavenger on he bad block.

<rdar://problem/9898200>

Modified:
    llvm/trunk/lib/CodeGen/BranchFolding.cpp

Modified: llvm/trunk/lib/CodeGen/BranchFolding.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/CodeGen/BranchFolding.cpp?rev=136973&r1=136972&r2=136973&view=diff
==============================================================================
--- llvm/trunk/lib/CodeGen/BranchFolding.cpp (original)
+++ llvm/trunk/lib/CodeGen/BranchFolding.cpp Fri Aug  5 13:47:07 2011
@@ -1624,26 +1624,29 @@
     if (!TIB->isSafeToMove(TII, 0, DontMoveAcrossStore))
       break;
 
+    // Remove kills from LocalDefsSet, these registers had short live ranges.
+    for (unsigned i = 0, e = TIB->getNumOperands(); i != e; ++i) {
+      MachineOperand &MO = TIB->getOperand(i);
+      if (!MO.isReg() || !MO.isUse() || !MO.isKill())
+        continue;
+      unsigned Reg = MO.getReg();
+      if (!Reg || !LocalDefsSet.count(Reg))
+        continue;
+      for (const unsigned *OR = TRI->getOverlaps(Reg); *OR; ++OR)
+        LocalDefsSet.erase(*OR);
+    }
+
     // Track local defs so we can update liveins.
     for (unsigned i = 0, e = TIB->getNumOperands(); i != e; ++i) {
       MachineOperand &MO = TIB->getOperand(i);
-      if (!MO.isReg())
+      if (!MO.isReg() || !MO.isDef() || MO.isDead())
         continue;
       unsigned Reg = MO.getReg();
       if (!Reg)
         continue;
-      if (MO.isDef()) {
-        if (!MO.isDead()) {
-          LocalDefs.push_back(Reg);
-          LocalDefsSet.insert(Reg);
-          for (const unsigned *SR = TRI->getSubRegisters(Reg); *SR; ++SR)
-            LocalDefsSet.insert(*SR);
-        }
-      } else if (MO.isKill() && LocalDefsSet.count(Reg)) {
-        LocalDefsSet.erase(Reg);
-        for (const unsigned *SR = TRI->getSubRegisters(Reg); *SR; ++SR)
-          LocalDefsSet.erase(*SR);
-      }
+      LocalDefs.push_back(Reg);
+      for (const unsigned *OR = TRI->getOverlaps(Reg); *OR; ++OR)
+        LocalDefsSet.insert(*OR);
     }
 
     HasDups = true;;