Add class MipsAnalyzeImmediate which comes up with an instruction sequence to

load an immediate. 



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@148900 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 153 insertions, 0 deletions

diff --git a/lib/Target/Mips/MipsAnalyzeImmediate.cpp b/lib/Target/Mips/MipsAnalyzeImmediate.cpp
new file mode 100644
index 0000000000..c81c820fa3
--- /dev/null
+++ b/lib/Target/Mips/MipsAnalyzeImmediate.cpp
@@ -0,0 +1,153 @@
+//===-- MipsAnalyzeImmediate.cpp - Analyze immediates ---------------------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+#include "MipsAnalyzeImmediate.h"
+#include "Mips.h"
+#include "llvm/Support/MathExtras.h"
+
+using namespace llvm;
+
+MipsAnalyzeImmediate::Inst::Inst(unsigned O, unsigned I) : Opc(O), ImmOpnd(I) {}
+
+// Add I to the instruction sequences.
+void MipsAnalyzeImmediate::AddInstr(InstSeqLs &SeqLs, const Inst &I) {
+  // Add an instruction seqeunce consisting of just I.
+  if (SeqLs.empty()) {
+    SeqLs.push_back(InstSeq(1, I));
+    return;
+  }
+
+  for (InstSeqLs::iterator Iter = SeqLs.begin(); Iter != SeqLs.end(); ++Iter)
+    Iter->push_back(I);
+}
+
+void MipsAnalyzeImmediate::GetInstSeqLsADDiu(int64_t Imm, unsigned RemSize,
+                                             InstSeqLs &SeqLs) {
+  GetInstSeqLs((Imm + 0x8000) & ~0xffff, RemSize, SeqLs);
+  AddInstr(SeqLs, Inst(ADDiu, Imm & 0xffff));
+}
+
+void MipsAnalyzeImmediate::GetInstSeqLsORi(int64_t Imm, unsigned RemSize,
+                                           InstSeqLs &SeqLs) {
+  GetInstSeqLs(Imm & ~0xffff, RemSize, SeqLs);
+  AddInstr(SeqLs, Inst(ORi, Imm & 0xffff));
+}
+
+void MipsAnalyzeImmediate::GetInstSeqLsSLL(int64_t Imm, unsigned RemSize,
+                                           InstSeqLs &SeqLs) {
+  unsigned Shamt = CountTrailingZeros_64(Imm);
+  GetInstSeqLs(Imm >> Shamt, RemSize - Shamt, SeqLs);
+  AddInstr(SeqLs, Inst(SLL, Shamt));
+}
+
+void MipsAnalyzeImmediate::GetInstSeqLs(int64_t Imm, unsigned RemSize,
+                                        InstSeqLs &SeqLs) {
+  int64_t MaskedImm = Imm & (((uint64_t)-1) >> (64 - Size));
+
+  // Do nothing if Imm is 0.
+  if (!MaskedImm)
+    return;
+
+  // A single ADDiu will do if RemSize <= 16.
+  if (RemSize <= 16) {
+    AddInstr(SeqLs, Inst(ADDiu, MaskedImm));
+    return;
+  }
+
+  // Shift if the lower 16-bit is cleared.
+  if (!(Imm & 0xffff)) {
+    GetInstSeqLsSLL(Imm, RemSize, SeqLs);
+    return;
+  }
+
+  GetInstSeqLsADDiu(Imm, RemSize, SeqLs);
+
+  // If bit 15 is cleared, it doesn't make a difference whether the last
+  // instruction is an ADDiu or ORi. In that case, do not call GetInstSeqLsORi.
+  if (Imm & 0x8000) {
+    InstSeqLs SeqLsORi;
+    GetInstSeqLsORi(Imm, RemSize, SeqLsORi);
+    SeqLs.insert(SeqLs.end(), SeqLsORi.begin(), SeqLsORi.end());
+  }
+}
+
+// Replace a ADDiu & SLL pair with a LUi.
+// e.g. the following two instructions 
+//  ADDiu 0x0111
+//  SLL 18
+// are replaced with
+//  LUi 0x444
+void MipsAnalyzeImmediate::ReplaceADDiuSLLWithLUi(InstSeq &Seq) {
+  // Check if the first two instructions are ADDiu and SLL and the shift amount
+  // is at least 16.
+  if ((Seq.size() < 2) || (Seq[0].Opc != ADDiu) ||
+      (Seq[1].Opc != SLL) || (Seq[1].ImmOpnd < 16))
+    return;
+
+  // Sign-extend and shift operand of ADDiu and see if it still fits in 16-bit.
+  int64_t Imm = (((int64_t)Seq[0].ImmOpnd) << 48) >> 48;
+  int64_t ShiftedImm = Imm << (Seq[1].ImmOpnd - 16);
+
+  if (!isInt<16>(ShiftedImm))
+    return;
+
+  // Replace the first instruction and erase the second.
+  Seq[0].Opc = LUi;
+  Seq[0].ImmOpnd = (unsigned)(ShiftedImm & 0xffff);
+  Seq.erase(Seq.begin() + 1);
+}
+
+void MipsAnalyzeImmediate::GetShortestSeq(InstSeqLs &SeqLs, InstSeq &Insts) {
+  InstSeqLs::iterator ShortestSeq = SeqLs.end();
+  // The length of an instruction sequence is at most 7.
+  unsigned ShortestLength = 8;
+
+  for (InstSeqLs::iterator S = SeqLs.begin(); S != SeqLs.end(); ++S) {
+    ReplaceADDiuSLLWithLUi(*S);
+    assert(S->size() <= 7);
+
+    if (S->size() < ShortestLength) {
+      ShortestSeq = S;
+      ShortestLength = S->size();
+    }
+  }
+
+  Insts.clear();
+  Insts.append(ShortestSeq->begin(), ShortestSeq->end());
+}
+
+const MipsAnalyzeImmediate::InstSeq
+&MipsAnalyzeImmediate::Analyze(int64_t Imm, unsigned Size,
+                               bool LastInstrIsADDiu) {
+  this->Size = Size;
+
+  if (Size == 32) {
+    ADDiu = Mips::ADDiu;
+    ORi = Mips::ORi;
+    SLL = Mips::SLL;
+    LUi = Mips::LUi;
+  } else {
+    ADDiu = Mips::DADDiu;
+    ORi = Mips::ORi64;
+    SLL = Mips::DSLL;
+    LUi = Mips::LUi64;
+  }
+
+  InstSeqLs SeqLs;
+
+  // Get the list of instruction sequences.
+  if (LastInstrIsADDiu | !Imm)
+    GetInstSeqLsADDiu(Imm, Size, SeqLs);
+  else
+    GetInstSeqLs(Imm, Size, SeqLs);
+
+  // Set Insts to the shortest instruction sequence.
+  GetShortestSeq(SeqLs, Insts);
+
+  return Insts;  
+}