When Mips16 frames grow large, the immediate field may exceed the maximum

allowed size for the instruction. This code uses RegScavenger to fix this.
We sometimes need 2 registers for Mips16 so we must handle things
differently than how register scavenger is normally used.



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@174696 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 72 insertions, 3 deletions

diff --git a/lib/Target/Mips/Mips16InstrInfo.cpp b/lib/Target/Mips/Mips16InstrInfo.cpp
index 117faea86f..9f27ac3517 100644
--- a/lib/Target/Mips/Mips16InstrInfo.cpp
+++ b/lib/Target/Mips/Mips16InstrInfo.cpp
@@ -19,6 +19,7 @@
 #include "llvm/ADT/StringRef.h"
 #include "llvm/CodeGen/MachineInstrBuilder.h"
 #include "llvm/CodeGen/MachineRegisterInfo.h"
+#include "llvm/CodeGen/RegisterScavenging.h"
 #include "llvm/Support/CommandLine.h"
 #include "llvm/Support/ErrorHandling.h"
 #include "llvm/Support/TargetRegistry.h"
@@ -306,11 +307,79 @@ void Mips16InstrInfo::adjustStackPtr(unsigned SP, int64_t Amount,
 /// This function generates the sequence of instructions needed to get the
 /// result of adding register REG and immediate IMM.
 unsigned
-Mips16InstrInfo::loadImmediate(int64_t Imm, MachineBasicBlock &MBB,
+Mips16InstrInfo::loadImmediate(unsigned FrameReg,
+                               int64_t Imm, MachineBasicBlock &MBB,
                                MachineBasicBlock::iterator II, DebugLoc DL,
-                               unsigned *NewImm) const {
+                               unsigned &NewImm) const {
+  //
+  // given original instruction is:
+  // Instr rx, T[offset] where offset is too big.
+  //
+  // lo = offset & 0xFFFF
+  // hi = ((offset >> 16) + (lo >> 15)) & 0xFFFF;
+  //
+  // let T = temporary register
+  // li T, hi
+  // shl T, 16
+  // add T, Rx, T
+  //
+  RegScavenger rs;
+  int32_t lo = Imm & 0xFFFF;
+  int32_t hi = ((Imm >> 16) + (lo >> 15)) & 0xFFFF;
+  NewImm = lo;
+  unsigned Reg =0;
+  unsigned SpReg = 0;
+  rs.enterBasicBlock(&MBB);
+  rs.forward(II);
+  //
+  // we use T0 for the first register, if we need to save something away.
+  // we use T1 for the second register, if we need to save something away.
+  //
+  unsigned FirstRegSaved =0, SecondRegSaved=0;
+  unsigned FirstRegSavedTo = 0, SecondRegSavedTo = 0;
+
+  Reg = rs.FindUnusedReg(&Mips::CPU16RegsRegClass);
+  if (Reg == 0) {
+    FirstRegSaved = Reg = Mips::V0;
+    FirstRegSavedTo = Mips::T0;
+    copyPhysReg(MBB, II, DL, FirstRegSavedTo, FirstRegSaved, true);
+  }
+  else
+    rs.setUsed(Reg);
+  BuildMI(MBB, II, DL, get(Mips::LiRxImmX16), Reg).addImm(hi);
+  BuildMI(MBB, II, DL, get(Mips::SllX16), Reg).addReg(Reg).
+    addImm(16);
+  if (FrameReg == Mips::SP) {
+    SpReg = rs.FindUnusedReg(&Mips::CPU16RegsRegClass);
+    if (SpReg == 0) {
+      if (Reg != Mips::V1) {
+        SecondRegSaved = SpReg = Mips::V1;
+        SecondRegSavedTo = Mips::T1;
+      }
+      else {
+        SecondRegSaved = SpReg = Mips::V0;
+        SecondRegSavedTo = Mips::T0;
+      }
+      copyPhysReg(MBB, II, DL, SecondRegSavedTo, SecondRegSaved, true);
+    }
+    else
+      rs.setUsed(SpReg);
 
-  return 0;
+    copyPhysReg(MBB, II, DL, SpReg, Mips::SP, false);
+    BuildMI(MBB, II, DL, get(Mips::  AdduRxRyRz16), Reg).addReg(SpReg)
+      .addReg(Reg);
+  }
+  else
+    BuildMI(MBB, II, DL, get(Mips::  AdduRxRyRz16), Reg).addReg(FrameReg)
+      .addReg(Reg, RegState::Kill);
+  if (FirstRegSaved || SecondRegSaved) {
+    II = llvm::next(II);
+    if (FirstRegSaved)
+      copyPhysReg(MBB, II, DL, FirstRegSaved, FirstRegSavedTo, true);
+    if (SecondRegSaved)
+      copyPhysReg(MBB, II, DL, SecondRegSaved, SecondRegSavedTo, true);
+  }
+  return Reg;
 }
 
 unsigned Mips16InstrInfo::GetAnalyzableBrOpc(unsigned Opc) const {