Peephole opt needs optimizeSelect() to keep track of newly created MIs

Peephole optimizer is scanning a basic block forward. At some point it 
needs to answer the question "given a pointer to an MI in the current 
BB, is it located before or after the current instruction".
To perform this, it keeps a set of the MIs already seen during the scan, 
if a MI is not in the set, it is assumed to be after.
It means that newly created MIs have to be inserted in the set as well.

This commit passes the set as an argument to the target-dependent 
optimizeSelect() so that it can properly update the set with the 
(potentially) newly created MIs.



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@225772 91177308-0d34-0410-b5e6-96231b3b80d8

include/llvm/Target/TargetInstrInfo.h

@@ -603,9 +603,12 @@ public:
   /// a side.
   ///
   /// @param MI          Optimizable select instruction.
+  /// @param SeenMIs     Set that record all MIs in the basic block up to \p
+  /// MI. Has to be updated with any newly created MI or deleted ones.
   /// @param PreferFalse Try to optimize FalseOp instead of TrueOp.
   /// @returns Optimized instruction or NULL.
   virtual MachineInstr *optimizeSelect(MachineInstr *MI,
+                                       SmallPtrSetImpl<MachineInstr *> &NewMIs,
                                        bool PreferFalse = false) const {
     // This function must be implemented if Optimizable is ever set.
     llvm_unreachable("Target must implement TargetInstrInfo::optimizeSelect!");

lib/CodeGen/PeepholeOptimizer.cpp

@@ -133,7 +133,8 @@ namespace {
     bool optimizeCmpInstr(MachineInstr *MI, MachineBasicBlock *MBB);
     bool optimizeExtInstr(MachineInstr *MI, MachineBasicBlock *MBB,
                           SmallPtrSetImpl<MachineInstr*> &LocalMIs);
-    bool optimizeSelect(MachineInstr *MI);
+    bool optimizeSelect(MachineInstr *MI,
+                        SmallPtrSetImpl<MachineInstr *> &LocalMIs);
     bool optimizeCondBranch(MachineInstr *MI);
     bool optimizeCopyOrBitcast(MachineInstr *MI);
     bool optimizeCoalescableCopy(MachineInstr *MI);
@@ -482,7 +483,8 @@ bool PeepholeOptimizer::optimizeCmpInstr(MachineInstr *MI,
 }
 
 /// Optimize a select instruction.
-bool PeepholeOptimizer::optimizeSelect(MachineInstr *MI) {
+bool PeepholeOptimizer::optimizeSelect(MachineInstr *MI,
+                            SmallPtrSetImpl<MachineInstr *> &LocalMIs) {
   unsigned TrueOp = 0;
   unsigned FalseOp = 0;
   bool Optimizable = false;
@@ -491,7 +493,7 @@ bool PeepholeOptimizer::optimizeSelect(MachineInstr *MI) {
     return false;
   if (!Optimizable)
     return false;
-  if (!TII->optimizeSelect(MI))
+  if (!TII->optimizeSelect(MI, LocalMIs))
     return false;
   MI->eraseFromParent();
   ++NumSelects;
@@ -1072,6 +1074,13 @@ bool PeepholeOptimizer::runOnMachineFunction(MachineFunction &MF) {
     MachineBasicBlock *MBB = &*I;
 
     bool SeenMoveImm = false;
+
+    // During this forward scan, at some point it needs to answer the question
+    // "given a pointer to an MI in the current BB, is it located before or
+    // after the current instruction".
+    // To perform this, the following set keeps track of the MIs already seen
+    // during the scan, if a MI is not in the set, it is assumed to be located
+    // after. Newly created MIs have to be inserted in the set as well.
     SmallPtrSet<MachineInstr*, 16> LocalMIs;
     SmallSet<unsigned, 4> ImmDefRegs;
     DenseMap<unsigned, MachineInstr*> ImmDefMIs;
@@ -1102,7 +1111,7 @@ bool PeepholeOptimizer::runOnMachineFunction(MachineFunction &MF) {
       if ((isUncoalescableCopy(*MI) &&
            optimizeUncoalescableCopy(MI, LocalMIs)) ||
           (MI->isCompare() && optimizeCmpInstr(MI, MBB)) ||
-          (MI->isSelect() && optimizeSelect(MI))) {
+          (MI->isSelect() && optimizeSelect(MI, LocalMIs))) {
         // MI is deleted.
         LocalMIs.erase(MI);
         Changed = true;

lib/Target/ARM/ARMBaseInstrInfo.cpp

@@ -1836,8 +1836,10 @@ bool ARMBaseInstrInfo::analyzeSelect(const MachineInstr *MI,
   return false;
 }
 
-MachineInstr *ARMBaseInstrInfo::optimizeSelect(MachineInstr *MI,
-                                               bool PreferFalse) const {
+MachineInstr *
+ARMBaseInstrInfo::optimizeSelect(MachineInstr *MI,
+                                 SmallPtrSetImpl<MachineInstr *> &SeenMIs,
+                                 bool PreferFalse) const {
   assert((MI->getOpcode() == ARM::MOVCCr || MI->getOpcode() == ARM::t2MOVCCr) &&
          "Unknown select instruction");
   MachineRegisterInfo &MRI = MI->getParent()->getParent()->getRegInfo();
@@ -1885,6 +1887,10 @@ MachineInstr *ARMBaseInstrInfo::optimizeSelect(MachineInstr *MI,
   NewMI.addOperand(FalseReg);
   NewMI->tieOperands(0, NewMI->getNumOperands() - 1);
 
+  // Update SeenMIs set: register newly created MI and erase removed DefMI.
+  SeenMIs.insert(NewMI);
+  SeenMIs.erase(DefMI);
+
   // The caller will erase MI, but not DefMI.
   DefMI->eraseFromParent();
   return NewMI;

lib/Target/ARM/ARMBaseInstrInfo.h

@@ -261,7 +261,9 @@ public:
                      unsigned &TrueOp, unsigned &FalseOp,
                      bool &Optimizable) const override;
 
-  MachineInstr *optimizeSelect(MachineInstr *MI, bool) const override;
+  MachineInstr *optimizeSelect(MachineInstr *MI,
+                               SmallPtrSetImpl<MachineInstr *> &SeenMIs,
+                               bool) const override;
 
   /// FoldImmediate - 'Reg' is known to be defined by a move immediate
   /// instruction, try to fold the immediate into the use instruction.