R600/SI: Add instruction shrinking pass

This pass converts 64-bit instructions to 32-bit when possible.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@213561 91177308-0d34-0410-b5e6-96231b3b80d8

lib/Target/R600/SIShrinkInstructions.cpp

@@ -0,0 +1,189 @@
+//===-- SIShrinkInstructions.cpp - Shrink Instructions --------------------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+/// The pass tries to use the 32-bit encoding for instructions when possible.
+//===----------------------------------------------------------------------===//
+//
+
+#include "AMDGPU.h"
+#include "SIInstrInfo.h"
+#include "llvm/ADT/Statistic.h"
+#include "llvm/CodeGen/MachineFunctionPass.h"
+#include "llvm/CodeGen/MachineInstrBuilder.h"
+#include "llvm/CodeGen/MachineRegisterInfo.h"
+#include "llvm/IR/LLVMContext.h"
+#include "llvm/IR/Function.h"
+#include "llvm/Support/Debug.h"
+#include "llvm/Target/TargetMachine.h"
+
+#define DEBUG_TYPE "si-shrink-instructions"
+
+STATISTIC(NumInstructionsShrunk,
+          "Number of 64-bit instruction reduced to 32-bit.");
+
+namespace llvm {
+  void initializeSIShrinkInstructionsPass(PassRegistry&);
+}
+
+using namespace llvm;
+
+namespace {
+
+class SIShrinkInstructions : public MachineFunctionPass {
+public:
+  static char ID;
+
+public:
+  SIShrinkInstructions() : MachineFunctionPass(ID) {
+  }
+
+  virtual bool runOnMachineFunction(MachineFunction &MF) override;
+
+  virtual const char *getPassName() const override {
+    return "SI Shrink Instructions";
+  }
+
+  virtual void getAnalysisUsage(AnalysisUsage &AU) const override {
+    AU.setPreservesCFG();
+    MachineFunctionPass::getAnalysisUsage(AU);
+  }
+};
+
+} // End anonymous namespace.
+
+INITIALIZE_PASS_BEGIN(SIShrinkInstructions, DEBUG_TYPE,
+                      "SI Lower il Copies", false, false)
+INITIALIZE_PASS_END(SIShrinkInstructions, DEBUG_TYPE,
+                    "SI Lower il Copies", false, false)
+
+char SIShrinkInstructions::ID = 0;
+
+FunctionPass *llvm::createSIShrinkInstructionsPass() {
+  return new SIShrinkInstructions();
+}
+
+static bool isVGPR(const MachineOperand *MO, const SIRegisterInfo &TRI,
+                   const MachineRegisterInfo &MRI) {
+  if (!MO->isReg())
+    return false;
+
+  if (TargetRegisterInfo::isVirtualRegister(MO->getReg()))
+    return TRI.hasVGPRs(MRI.getRegClass(MO->getReg()));
+
+  return TRI.hasVGPRs(TRI.getPhysRegClass(MO->getReg()));
+}
+
+static bool canShrink(MachineInstr &MI, const SIInstrInfo *TII,
+                      const SIRegisterInfo &TRI,
+                      const MachineRegisterInfo &MRI) {
+
+  const MachineOperand *Src2 = TII->getNamedOperand(MI, AMDGPU::OpName::src2);
+  // Can't shrink instruction with three operands.
+  if (Src2)
+    return false;
+
+  const MachineOperand *Src1 = TII->getNamedOperand(MI, AMDGPU::OpName::src1);
+  const MachineOperand *Src1Mod =
+      TII->getNamedOperand(MI, AMDGPU::OpName::src1_modifiers);
+
+  if (Src1 && (!isVGPR(Src1, TRI, MRI) || Src1Mod->getImm() != 0))
+    return false;
+
+  // We don't need to check src0, all input types are legal, so just make
+  // sure src0 isn't using any modifiers.
+  const MachineOperand *Src0Mod =
+      TII->getNamedOperand(MI, AMDGPU::OpName::src0_modifiers);
+  if (Src0Mod && Src0Mod->getImm() != 0)
+    return false;
+
+  // Check output modifiers
+  const MachineOperand *Omod = TII->getNamedOperand(MI, AMDGPU::OpName::omod);
+  if (Omod && Omod->getImm() != 0)
+    return false;
+
+  const MachineOperand *Clamp = TII->getNamedOperand(MI, AMDGPU::OpName::clamp);
+  return !Clamp || Clamp->getImm() == 0;
+}
+
+bool SIShrinkInstructions::runOnMachineFunction(MachineFunction &MF) {
+  MachineRegisterInfo &MRI = MF.getRegInfo();
+  const SIInstrInfo *TII = static_cast<const SIInstrInfo *>(
+      MF.getTarget().getInstrInfo());
+  const SIRegisterInfo &TRI = TII->getRegisterInfo();
+  std::vector<unsigned> I1Defs;
+
+  for (MachineFunction::iterator BI = MF.begin(), BE = MF.end();
+                                                  BI != BE; ++BI) {
+
+    MachineBasicBlock &MBB = *BI;
+    MachineBasicBlock::iterator I, Next;
+    for (I = MBB.begin(); I != MBB.end(); I = Next) {
+      Next = std::next(I);
+      MachineInstr &MI = *I;
+
+      int Op32 = AMDGPU::getVOPe32(MI.getOpcode());
+
+      if (Op32 == -1)
+        continue;
+
+      if (!canShrink(MI, TII, TRI, MRI)) {
+        // Try commtuing the instruction and see if that enables us to shrink
+        // it.
+        if (!MI.isCommutable() || !TII->commuteInstruction(&MI) ||
+            !canShrink(MI, TII, TRI, MRI))
+          continue;
+      }
+
+      if (TII->isVOPC(Op32)) {
+        unsigned DstReg = MI.getOperand(0).getReg();
+        if (TargetRegisterInfo::isVirtualRegister(DstReg)) {
+          // VOPC instructions can only write to the VCC register.  We can't
+          // force them to use VCC here, because the register allocator
+          // has trouble with sequences like this, which cause the allocator
+          // to run out of registes if vreg0 and vreg1 belong to the VCCReg
+          // register class:
+          // vreg0 = VOPC;
+          // vreg1 = VOPC;
+          // S_AND_B64 vreg0, vreg1
+          //
+          // So, instead of forcing the instruction to write to VCC, we provide a
+          // hint to the register allocator to use VCC and then we
+          // we will run this pass again after RA and shrink it if it outpus to
+          // VCC.
+          MRI.setRegAllocationHint(MI.getOperand(0).getReg(), 0, AMDGPU::VCC);
+          continue;
+        }
+        if (DstReg != AMDGPU::VCC)
+          continue;
+      }
+
+      // We can shrink this instruction
+      DEBUG(dbgs() << "Shrinking "; MI.dump(); dbgs() << "\n";);
+
+      MachineInstrBuilder MIB =
+          BuildMI(MBB, I, MI.getDebugLoc(), TII->get(Op32));
+
+      // dst
+      MIB.addOperand(MI.getOperand(0));
+
+      MIB.addOperand(*TII->getNamedOperand(MI, AMDGPU::OpName::src0));
+
+      const MachineOperand *Src1 =
+          TII->getNamedOperand(MI, AMDGPU::OpName::src1);
+      if (Src1)
+        MIB.addOperand(*Src1);
+
+      for (const MachineOperand &MO : MI.implicit_operands())
+        MIB.addOperand(MO);
+
+      DEBUG(dbgs() << "e32 MI = "; MI.dump(); dbgs() << "\n";);
+      ++NumInstructionsShrunk;
+      MI.eraseFromParent();
+    }
+  }
+  return false;
+}