1 files changed, 56 insertions, 5 deletions

diff --git a/llvm/lib/Target/SystemZ/SystemZElimCompare.cpp b/llvm/lib/Target/SystemZ/SystemZElimCompare.cpp
index b292b554779..6e42e283c9f 100644
--- a/llvm/lib/Target/SystemZ/SystemZElimCompare.cpp
+++ b/llvm/lib/Target/SystemZ/SystemZElimCompare.cpp
@@ -28,6 +28,7 @@ using namespace llvm;
 #define DEBUG_TYPE "systemz-elim-compare"
 
 STATISTIC(BranchOnCounts, "Number of branch-on-count instructions");
+STATISTIC(LoadAndTraps, "Number of load-and-trap instructions");
 STATISTIC(EliminatedComparisons, "Number of eliminated comparisons");
 STATISTIC(FusedComparisons, "Number of fused compare-and-branch instructions");
 
@@ -73,6 +74,8 @@ private:
   Reference getRegReferences(MachineInstr &MI, unsigned Reg);
   bool convertToBRCT(MachineInstr &MI, MachineInstr &Compare,
                      SmallVectorImpl<MachineInstr *> &CCUsers);
+  bool convertToLoadAndTrap(MachineInstr &MI, MachineInstr &Compare,
+                            SmallVectorImpl<MachineInstr *> &CCUsers);
   bool convertToLoadAndTest(MachineInstr &MI);
   bool adjustCCMasksForInstr(MachineInstr &MI, MachineInstr &Compare,
                              SmallVectorImpl<MachineInstr *> &CCUsers);
@@ -225,6 +228,48 @@ bool SystemZElimCompare::convertToBRCT(
   return true;
 }
 
+// Compare compares the result of MI against zero.  If MI is a suitable load
+// instruction and if CCUsers is a single conditional trap on zero, eliminate
+// the load and convert the branch to a load-and-trap.  Return true on success.
+bool SystemZElimCompare::convertToLoadAndTrap(
+    MachineInstr &MI, MachineInstr &Compare,
+    SmallVectorImpl<MachineInstr *> &CCUsers) {
+  unsigned LATOpcode = TII->getLoadAndTrap(MI.getOpcode());
+  if (!LATOpcode)
+    return false;
+
+  // Check whether we have a single CondTrap that traps on zero.
+  if (CCUsers.size() != 1)
+    return false;
+  MachineInstr *Branch = CCUsers[0];
+  if (Branch->getOpcode() != SystemZ::CondTrap ||
+      Branch->getOperand(0).getImm() != SystemZ::CCMASK_ICMP ||
+      Branch->getOperand(1).getImm() != SystemZ::CCMASK_CMP_EQ)
+    return false;
+
+  // We already know that there are no references to the register between
+  // MI and Compare.  Make sure that there are also no references between
+  // Compare and Branch.
+  unsigned SrcReg = getCompareSourceReg(Compare);
+  MachineBasicBlock::iterator MBBI = Compare, MBBE = Branch;
+  for (++MBBI; MBBI != MBBE; ++MBBI)
+    if (getRegReferences(*MBBI, SrcReg))
+      return false;
+
+  // The transformation is OK.  Rebuild Branch as a load-and-trap.
+  MachineOperand Target(Branch->getOperand(2));
+  while (Branch->getNumOperands())
+    Branch->RemoveOperand(0);
+  Branch->setDesc(TII->get(LATOpcode));
+  MachineInstrBuilder(*Branch->getParent()->getParent(), Branch)
+      .addOperand(MI.getOperand(0))
+      .addOperand(MI.getOperand(1))
+      .addOperand(MI.getOperand(2))
+      .addOperand(MI.getOperand(3));
+  MI.eraseFromParent();
+  return true;
+}
+
 // If MI is a load instruction, try to convert it into a LOAD AND TEST.
 // Return true on success.
 bool SystemZElimCompare::convertToLoadAndTest(MachineInstr &MI) {
@@ -353,11 +398,17 @@ bool SystemZElimCompare::optimizeCompareZero(
     MachineInstr &MI = *MBBI;
     if (resultTests(MI, SrcReg)) {
       // Try to remove both MI and Compare by converting a branch to BRCT(G).
-      // We don't care in this case whether CC is modified between MI and
-      // Compare.
-      if (!CCRefs.Use && !SrcRefs && convertToBRCT(MI, Compare, CCUsers)) {
-        BranchOnCounts += 1;
-        return true;
+      // or a load-and-trap instruction.  We don't care in this case whether
+      // CC is modified between MI and Compare.
+      if (!CCRefs.Use && !SrcRefs) {
+        if (convertToBRCT(MI, Compare, CCUsers)) {
+          BranchOnCounts += 1;
+          return true;
+        }
+        if (convertToLoadAndTrap(MI, Compare, CCUsers)) {
+          LoadAndTraps += 1;
+          return true;
+        }
       }
       // Try to eliminate Compare by reusing a CC result from MI.
       if ((!CCRefs && convertToLoadAndTest(MI)) ||