1 files changed, 40 insertions, 11 deletions

diff --git a/lib/CodeGen/CriticalAntiDepBreaker.cpp b/lib/CodeGen/CriticalAntiDepBreaker.cpp
index 822636f..d3ffcc7 100644
--- a/lib/CodeGen/CriticalAntiDepBreaker.cpp
+++ b/lib/CodeGen/CriticalAntiDepBreaker.cpp
@@ -146,8 +146,8 @@ static const SDep *CriticalPathStep(const SUnit *SU) {
 
 void CriticalAntiDepBreaker::PrescanInstruction(MachineInstr *MI) {
   // It's not safe to change register allocation for source operands of
-  // that have special allocation requirements. Also assume all registers
-  // used in a call must not be changed (ABI).
+  // instructions that have special allocation requirements. Also assume all
+  // registers used in a call must not be changed (ABI).
   // FIXME: The issue with predicated instruction is more complex. We are being
   // conservative here because the kill markers cannot be trusted after
   // if-conversion:
@@ -200,6 +200,28 @@ void CriticalAntiDepBreaker::PrescanInstruction(MachineInstr *MI) {
     if (Classes[Reg] != reinterpret_cast<TargetRegisterClass *>(-1))
       RegRefs.insert(std::make_pair(Reg, &MO));
 
+    // If this reg is tied and live (Classes[Reg] is set to -1), we can't change
+    // it or any of its sub or super regs. We need to use KeepRegs to mark the
+    // reg because not all uses of the same reg within an instruction are
+    // necessarily tagged as tied.
+    // Example: an x86 "xor %eax, %eax" will have one source operand tied to the
+    // def register but not the second (see PR20020 for details).
+    // FIXME: can this check be relaxed to account for undef uses
+    // of a register? In the above 'xor' example, the uses of %eax are undef, so
+    // earlier instructions could still replace %eax even though the 'xor'
+    // itself can't be changed.
+    if (MI->isRegTiedToUseOperand(i) &&
+        Classes[Reg] == reinterpret_cast<TargetRegisterClass *>(-1)) {
+      for (MCSubRegIterator SubRegs(Reg, TRI, /*IncludeSelf=*/true);
+           SubRegs.isValid(); ++SubRegs) {
+        KeepRegs.set(*SubRegs);
+      }
+      for (MCSuperRegIterator SuperRegs(Reg, TRI);
+           SuperRegs.isValid(); ++SuperRegs) {
+        KeepRegs.set(*SuperRegs);
+      }
+    }
+
     if (MO.isUse() && Special) {
       if (!KeepRegs.test(Reg)) {
         for (MCSubRegIterator SubRegs(Reg, TRI, /*IncludeSelf=*/true);
@@ -236,9 +258,15 @@ void CriticalAntiDepBreaker::ScanInstruction(MachineInstr *MI,
       unsigned Reg = MO.getReg();
       if (Reg == 0) continue;
       if (!MO.isDef()) continue;
+
+      // If we've already marked this reg as unchangeable, carry on.
+      if (KeepRegs.test(Reg)) continue;
+      
       // Ignore two-addr defs.
       if (MI->isRegTiedToUseOperand(i)) continue;
 
+      // FIXME: we should use a SubRegIterator that includes self (as above), so
+      // we don't have to repeat all this code for the reg itself.
       DefIndices[Reg] = Count;
       KillIndices[Reg] = ~0u;
       assert(((KillIndices[Reg] == ~0u) !=
@@ -281,6 +309,9 @@ void CriticalAntiDepBreaker::ScanInstruction(MachineInstr *MI,
 
     RegRefs.insert(std::make_pair(Reg, &MO));
 
+    // FIXME: we should use an MCRegAliasIterator that includes self so we don't
+    // have to repeat all this code for the reg itself.
+    
     // It wasn't previously live but now it is, this is a kill.
     if (KillIndices[Reg] == ~0u) {
       KillIndices[Reg] = Count;
@@ -309,7 +340,7 @@ void CriticalAntiDepBreaker::ScanInstruction(MachineInstr *MI,
 // the two-address instruction also defines NewReg, as may happen with
 // pre/postincrement loads. In this case, both the use and def operands are in
 // RegRefs because the def is inserted by PrescanInstruction and not erased
-// during ScanInstruction. So checking for an instructions with definitions of
+// during ScanInstruction. So checking for an instruction with definitions of
 // both NewReg and AntiDepReg covers it.
 bool
 CriticalAntiDepBreaker::isNewRegClobberedByRefs(RegRefIter RegRefBegin,
@@ -325,7 +356,7 @@ CriticalAntiDepBreaker::isNewRegClobberedByRefs(RegRefIter RegRefBegin,
     if (RefOper->isDef() && RefOper->isEarlyClobber())
       return true;
 
-    // Handle cases in which this instructions defines NewReg.
+    // Handle cases in which this instruction defines NewReg.
     MachineInstr *MI = RefOper->getParent();
     for (unsigned i = 0, e = MI->getNumOperands(); i != e; ++i) {
       const MachineOperand &CheckOper = MI->getOperand(i);
@@ -343,11 +374,11 @@ CriticalAntiDepBreaker::isNewRegClobberedByRefs(RegRefIter RegRefBegin,
         return true;
 
       // Don't allow an instruction using AntiDepReg to be earlyclobbered by
-      // NewReg
+      // NewReg.
       if (CheckOper.isEarlyClobber())
         return true;
 
-      // Don't allow inline asm to define NewReg at all. Who know what it's
+      // Don't allow inline asm to define NewReg at all. Who knows what it's
       // doing with it.
       if (MI->isInlineAsm())
         return true;
@@ -494,8 +525,7 @@ BreakAntiDependencies(const std::vector<SUnit>& SUnits,
   // as we go to help determine which registers are available.
   unsigned Broken = 0;
   unsigned Count = InsertPosIndex - 1;
-  for (MachineBasicBlock::iterator I = End, E = Begin;
-       I != E; --Count) {
+  for (MachineBasicBlock::iterator I = End, E = Begin; I != E; --Count) {
     MachineInstr *MI = --I;
     if (MI->isDebugValue())
       continue;
@@ -526,7 +556,7 @@ BreakAntiDependencies(const std::vector<SUnit>& SUnits,
             // Don't break anti-dependencies on non-allocatable registers.
             AntiDepReg = 0;
           else if (KeepRegs.test(AntiDepReg))
-            // Don't break anti-dependencies if an use down below requires
+            // Don't break anti-dependencies if a use down below requires
             // this exact register.
             AntiDepReg = 0;
           else {
@@ -564,8 +594,7 @@ BreakAntiDependencies(const std::vector<SUnit>& SUnits,
     // If MI's defs have a special allocation requirement, don't allow
     // any def registers to be changed. Also assume all registers
     // defined in a call must not be changed (ABI).
-    if (MI->isCall() || MI->hasExtraDefRegAllocReq() ||
-        TII->isPredicated(MI))
+    if (MI->isCall() || MI->hasExtraDefRegAllocReq() || TII->isPredicated(MI))
       // If this instruction's defs have special allocation requirement, don't
       // break this anti-dependency.
       AntiDepReg = 0;