Add a target hook to allow loads from constant pools to be rematerialized, and an

implementation for x86.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@37576 91177308-0d34-0410-b5e6-96231b3b80d8

include/llvm/Target/TargetInstrInfo.h

@@ -298,6 +298,16 @@ public:
     return 0;
   }
 
+  /// isOtherReMaterializableLoad - If the specified machine instruction is a
+  /// direct load that is trivially rematerializable, not counting loads from
+  /// stack slots, return true. If not, return false.  This predicate must
+  /// return false if the instruction has any side effects other than
+  /// producing the value from the load, or if it requres any address
+  /// registers that are not always available.
+  virtual bool isOtherReMaterializableLoad(MachineInstr *MI) const {
+    return false;
+  }
+
   /// convertToThreeAddress - This method must be implemented by targets that
   /// set the M_CONVERTIBLE_TO_3_ADDR flag.  When this flag is set, the target
   /// may be able to convert a two-address instruction into one or moretrue

lib/CodeGen/LiveIntervalAnalysis.cpp

@@ -336,12 +336,14 @@ void LiveIntervals::handleVirtualRegisterDef(MachineBasicBlock *mbb,
   // time we see a vreg.
   if (interval.empty()) {
     // Remember if the definition can be rematerialized. All load's from fixed
-    // stack slots are re-materializable.
+    // stack slots are re-materializable. The target may permit other loads to
+    // be re-materialized as well.
     int FrameIdx = 0;
     if (vi.DefInst &&
         (tii_->isReMaterializable(vi.DefInst->getOpcode()) ||
          (tii_->isLoadFromStackSlot(vi.DefInst, FrameIdx) &&
-          mf_->getFrameInfo()->isFixedObjectIndex(FrameIdx))))
+          mf_->getFrameInfo()->isFixedObjectIndex(FrameIdx)) ||
+         tii_->isOtherReMaterializableLoad(vi.DefInst)))
       interval.remat = vi.DefInst;
 
     // Get the Idx of the defining instructions.

lib/CodeGen/VirtRegMap.cpp

@@ -664,7 +664,8 @@ void LocalSpiller::RewriteMBB(MachineBasicBlock &MBB, VirtRegMap &VRM,
     // If this instruction is being rematerialized, just remove it!
     int FrameIdx;
     if ((TID->Flags & M_REMATERIALIZIBLE) ||
-        TII->isLoadFromStackSlot(&MI, FrameIdx)) {
+        TII->isLoadFromStackSlot(&MI, FrameIdx) ||
+        TII->isOtherReMaterializableLoad(&MI)) {
       bool Remove = true;
       for (unsigned i = 0, e = MI.getNumOperands(); i != e; ++i) {
         MachineOperand &MO = MI.getOperand(i);

lib/Target/X86/X86InstrInfo.cpp

@@ -112,6 +112,31 @@ unsigned X86InstrInfo::isStoreToStackSlot(MachineInstr *MI,
 }
 
 
+bool X86InstrInfo::isOtherReMaterializableLoad(MachineInstr *MI) const {
+  switch (MI->getOpcode()) {
+  default: break;
+  case X86::MOV8rm:
+  case X86::MOV16rm:
+  case X86::MOV16_rm:
+  case X86::MOV32rm:
+  case X86::MOV32_rm:
+  case X86::MOV64rm:
+  case X86::FpLD64m:
+  case X86::MOVSSrm:
+  case X86::MOVSDrm:
+  case X86::MOVAPSrm:
+  case X86::MOVAPDrm:
+  case X86::MMX_MOVD64rm:
+  case X86::MMX_MOVQ64rm:
+    return MI->getOperand(1).isRegister() && MI->getOperand(2).isImmediate() &&
+           MI->getOperand(3).isRegister() && MI->getOperand(4).isConstantPoolIndex() &&
+           MI->getOperand(1).getReg() == 0 &&
+           MI->getOperand(2).getImmedValue() == 1 &&
+           MI->getOperand(3).getReg() == 0;
+  }
+  return false;
+}
+
 /// convertToThreeAddress - This method must be implemented by targets that
 /// set the M_CONVERTIBLE_TO_3_ADDR flag.  When this flag is set, the target
 /// may be able to convert a two-address instruction into a true

lib/Target/X86/X86InstrInfo.h

@@ -239,6 +239,7 @@ public:
                    unsigned& destReg) const;
   unsigned isLoadFromStackSlot(MachineInstr *MI, int &FrameIndex) const;
   unsigned isStoreToStackSlot(MachineInstr *MI, int &FrameIndex) const;
+  bool isOtherReMaterializableLoad(MachineInstr *MI) const;
   
   /// convertToThreeAddress - This method must be implemented by targets that
   /// set the M_CONVERTIBLE_TO_3_ADDR flag.  When this flag is set, the target