[TwoAddressInstructionPass] Bugfix in handling of sunk instructions.

An instruction returned by TII->convertToThreeAddress() may contain a %noreg
(undef) operand, which is not expected by tryInstructionTransform(). So if
this MI is sunk to a lower point in MBB, it must be skipped when later
encountered.

A new set SunkInstrs is used for this purpose.

Note: there is no test supplied here, as this was triggered on SystemZ while
working on a review of instruction flags. A test case for this bugfix will be
included in the upcoming SystemZ commit.

Review: Quentin Colombet
https://reviews.llvm.org/D40711

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@319646 91177308-0d34-0410-b5e6-96231b3b80d8

lib/CodeGen/TwoAddressInstructionPass.cpp

@@ -110,6 +110,10 @@ class TwoAddressInstructionPass : public MachineFunctionPass {
   // Set of already processed instructions in the current block.
   SmallPtrSet<MachineInstr*, 8> Processed;
 
+  // Set of instructions converted to three-address by target and then sunk
+  // down current basic block.
+  SmallPtrSet<MachineInstr*, 8> SunkInstrs;
+
   // A map from virtual registers to physical registers which are likely targets
   // to be coalesced to due to copies from physical registers to virtual
   // registers. e.g. v1024 = move r0.
@@ -756,6 +760,8 @@ TwoAddressInstructionPass::convertInstTo3Addr(MachineBasicBlock::iterator &mi,
     mi = NewMI;
     nmi = std::next(mi);
   }
+  else
+    SunkInstrs.insert(NewMI);
 
   // Update source and destination register maps.
   SrcRegMap.erase(RegA);
@@ -1674,10 +1680,13 @@ bool TwoAddressInstructionPass::runOnMachineFunction(MachineFunction &Func) {
     SrcRegMap.clear();
     DstRegMap.clear();
     Processed.clear();
+    SunkInstrs.clear();
     for (MachineBasicBlock::iterator mi = MBB->begin(), me = MBB->end();
          mi != me; ) {
       MachineBasicBlock::iterator nmi = std::next(mi);
-      if (mi->isDebugValue()) {
+      // Don't revisit an instruction previously converted by target. It may
+      // contain undef register operands (%noreg), which are not handled.
+      if (mi->isDebugValue() || SunkInstrs.count(&*mi)) {
         mi = nmi;
         continue;
       }