[mips] Add assembler support for the "la $reg,symbol" pseudo-instruction.

[tomatabacu]

Summary

This pseudo-instruction allows the programmer to load an address from a symbolic expression into a register.

Patch by David Chisnall.
His work was sponsored by: DARPA, AFRL

I've made some minor changes to the original, such as improving the formatting and adding some comments, and I've also added a test case.

[dsanders]

LGTM with a formatting nit and one change to avoid creating objects that aren't used.

lib/Target/Mips/AsmParser/MipsAsmParser.cpp

1344–1349

These two shouldn't be created until we know we need them (which is in the if(isGP64bit()) block below).

1358

You'll need to sink this statement into the if-statement too.

1375–1379

I'd put braces around this since it spans several lines

[tomatabacu]

Addressed comments.
Also added the rest of the LUi-generating code inside the if-else, because it's much more readable this way.

[dsanders]

Thanks. LGTM with one whitespace nit I didn't notice the first time around.

test/MC/Mips/mips-expansions.s

20–35

Whitespace nit: Please align the start of the operand list for lui/ori to match the neighbouring instructions

[tomatabacu]

Addressed comment.

lib/Target/Mips/AsmParser/MipsAsmParser.cpp

bool expandLoadImm(MCInst &Inst, SMLoc IDLoc,
                      SmallVectorImpl<MCInst> &Instructions);
 
   bool expandLoadAddressImm(MCInst &Inst, SMLoc IDLoc,
                             SmallVectorImpl<MCInst> &Instructions);
 
   bool expandLoadAddressReg(MCInst &Inst, SMLoc IDLoc,
                             SmallVectorImpl<MCInst> &Instructions);
 
+  void expandLoadAddressSym(MCInst &Inst, SMLoc IDLoc,
+                            SmallVectorImpl<MCInst> &Instructions);
+
   void expandMemInst(MCInst &Inst, SMLoc IDLoc,
                      SmallVectorImpl<MCInst> &Instructions, bool isLoad,
                      bool isImmOpnd);
   bool reportParseError(Twine ErrorMsg);
   bool reportParseError(SMLoc Loc, Twine ErrorMsg);
 
   bool parseMemOffset(const MCExpr *&Res, bool isParenExpr);
   bool parseRelocOperand(const MCExpr *&Res);
bool MipsAsmParser::expandInstruction(MCInst &Inst, SMLoc IDLoc,
   case Mips::LoadAddr32Imm:
     return expandLoadAddressImm(Inst, IDLoc, Instructions);
   case Mips::LoadAddr32Reg:
     return expandLoadAddressReg(Inst, IDLoc, Instructions);
   }
 }
 
 namespace {
-template <int Shift, bool PerformShift>
-void createShiftOr(int64_t Value, unsigned RegNo, SMLoc IDLoc,
+template <bool PerformShift>
+void createShiftOr(MCOperand Operand, unsigned RegNo, SMLoc IDLoc,
                    SmallVectorImpl<MCInst> &Instructions) {
   MCInst tmpInst;
   if (PerformShift) {
     tmpInst.setOpcode(Mips::DSLL);
     tmpInst.addOperand(MCOperand::CreateReg(RegNo));
     tmpInst.addOperand(MCOperand::CreateReg(RegNo));
     tmpInst.addOperand(MCOperand::CreateImm(16));
     tmpInst.setLoc(IDLoc);
     Instructions.push_back(tmpInst);
     tmpInst.clear();
   }
   tmpInst.setOpcode(Mips::ORi);
   tmpInst.addOperand(MCOperand::CreateReg(RegNo));
   tmpInst.addOperand(MCOperand::CreateReg(RegNo));
-  tmpInst.addOperand(
-      MCOperand::CreateImm(((Value & (0xffffLL << Shift)) >> Shift)));
+  tmpInst.addOperand(Operand);
   tmpInst.setLoc(IDLoc);
   Instructions.push_back(tmpInst);
 }
+
+template <int Shift, bool PerformShift>
+void createShiftOr(int64_t Value, unsigned RegNo, SMLoc IDLoc,
+                   SmallVectorImpl<MCInst> &Instructions) {
+  createShiftOr<PerformShift>(
+      MCOperand::CreateImm(((Value & (0xffffLL << Shift)) >> Shift)), RegNo,
+      IDLoc, Instructions);
+}
 }
 
 bool MipsAsmParser::expandLoadImm(MCInst &Inst, SMLoc IDLoc,
                                   SmallVectorImpl<MCInst> &Instructions) {
   MCInst tmpInst;
   const MCOperand &ImmOp = Inst.getOperand(1);
   assert(ImmOp.isImm() && "expected immediate operand kind");
   const MCOperand &RegOp = Inst.getOperand(0);
bool MipsAsmParser::expandLoadImm(MCInst &Inst, SMLoc IDLoc,
   return false;
 }
 
 bool
 MipsAsmParser::expandLoadAddressReg(MCInst &Inst, SMLoc IDLoc,
                                     SmallVectorImpl<MCInst> &Instructions) {
   MCInst tmpInst;
   const MCOperand &ImmOp = Inst.getOperand(2);
-  assert(ImmOp.isImm() && "expected immediate operand kind");
+  assert((ImmOp.isImm() || ImmOp.isExpr()) &&
+         "expected immediate operand kind");
+  if (!ImmOp.isImm()) {
+    expandLoadAddressSym(Inst, IDLoc, Instructions);
+    return false;
+  }
   const MCOperand &SrcRegOp = Inst.getOperand(1);
   assert(SrcRegOp.isReg() && "expected register operand kind");
   const MCOperand &DstRegOp = Inst.getOperand(0);
   assert(DstRegOp.isReg() && "expected register operand kind");
   int ImmValue = ImmOp.getImm();
   if (-32768 <= ImmValue && ImmValue <= 65535) {
     // For -32768 <= j <= 65535.
     // la d,j(s) => addiu d,s,j
MipsAsmParser::expandLoadAddressReg(MCInst &Inst, SMLoc IDLoc,
   return false;
 }
 
 bool
 MipsAsmParser::expandLoadAddressImm(MCInst &Inst, SMLoc IDLoc,
                                     SmallVectorImpl<MCInst> &Instructions) {
   MCInst tmpInst;
   const MCOperand &ImmOp = Inst.getOperand(1);
-  assert(ImmOp.isImm() && "expected immediate operand kind");
+  assert((ImmOp.isImm() || ImmOp.isExpr()) &&
+         "expected immediate operand kind");
+  if (!ImmOp.isImm()) {
+    expandLoadAddressSym(Inst, IDLoc, Instructions);
+    return false;
+  }
   const MCOperand &RegOp = Inst.getOperand(0);
   assert(RegOp.isReg() && "expected register operand kind");
   int ImmValue = ImmOp.getImm();
   if (-32768 <= ImmValue && ImmValue <= 65535) {
     // For -32768 <= j <= 65535.
     // la d,j => addiu d,$zero,j
     tmpInst.setOpcode(Mips::ADDiu);
     tmpInst.addOperand(MCOperand::CreateReg(RegOp.getReg()));
if (-32768 <= ImmValue && ImmValue <= 65535) {
     tmpInst.addOperand(MCOperand::CreateReg(RegOp.getReg()));
     tmpInst.addOperand(MCOperand::CreateReg(RegOp.getReg()));
     tmpInst.addOperand(MCOperand::CreateImm(ImmValue & 0xffff));
     Instructions.push_back(tmpInst);
   }
   return false;
 }
 
+void
+MipsAsmParser::expandLoadAddressSym(MCInst &Inst, SMLoc IDLoc,
+                                    SmallVectorImpl<MCInst> &Instructions) {
+  // FIXME: If we do have a valid at register to use, we should generate a
+  // slightly shorter sequence here.
+  MCInst tmpInst;
+  int ExprOperandNo = 1;
+  // Sometimes the assembly parser will get the immediate expression as
+  // a $zero + an immediate.
+  if (Inst.getNumOperands() == 3) {
+    assert(Inst.getOperand(1).getReg() ==
+           (isGP64bit() ? Mips::ZERO_64 : Mips::ZERO));
+    ExprOperandNo = 2;
+  }
+  const MCOperand &SymOp = Inst.getOperand(ExprOperandNo);
+  assert(SymOp.isExpr() && "expected symbol operand kind");
+  const MCOperand &RegOp = Inst.getOperand(0);
+  unsigned RegNo = RegOp.getReg();
+  const MCSymbolRefExpr *Symbol = cast<MCSymbolRefExpr>(SymOp.getExpr());
+  const MCSymbolRefExpr *HiExpr =
+      MCSymbolRefExpr::Create(Symbol->getSymbol().getName(),
+                              MCSymbolRefExpr::VK_Mips_ABS_HI, getContext());
+  const MCSymbolRefExpr *LoExpr =
+      MCSymbolRefExpr::Create(Symbol->getSymbol().getName(),
+                              MCSymbolRefExpr::VK_Mips_ABS_LO, getContext());
+  if (isGP64bit()) {
+    // If it's a 64-bit architecture, expand to:
+    // la d,sym => lui  d,highest(sym)
+    //             ori  d,d,higher(sym)
+    //             dsll d,d,16
+    //             ori  d,d,hi16(sym)
+    //             dsll d,d,16
+    //             ori  d,d,lo16(sym)
+    const MCSymbolRefExpr *HighestExpr =
+        MCSymbolRefExpr::Create(Symbol->getSymbol().getName(),
+                                MCSymbolRefExpr::VK_Mips_HIGHEST, getContext());
+    const MCSymbolRefExpr *HigherExpr =
+        MCSymbolRefExpr::Create(Symbol->getSymbol().getName(),
+                                MCSymbolRefExpr::VK_Mips_HIGHER, getContext());
+
+    tmpInst.setOpcode(Mips::LUi);
+    tmpInst.addOperand(MCOperand::CreateReg(RegNo));
+    tmpInst.addOperand(MCOperand::CreateExpr(HighestExpr));
+    Instructions.push_back(tmpInst);
+
+    createShiftOr<false>(MCOperand::CreateExpr(HigherExpr), RegNo, SMLoc(),
+                         Instructions);
+    createShiftOr<true>(MCOperand::CreateExpr(HiExpr), RegNo, SMLoc(),
+                        Instructions);
+    createShiftOr<true>(MCOperand::CreateExpr(LoExpr), RegNo, SMLoc(),
+                        Instructions);
+  } else {
+    // Otherwise, expand to:
+    // la d,sym => lui  d,hi16(sym)
+    //             ori  d,d,lo16(sym)
+    tmpInst.setOpcode(Mips::LUi);
+    tmpInst.addOperand(MCOperand::CreateReg(RegNo));
+    tmpInst.addOperand(MCOperand::CreateExpr(HiExpr));
+    Instructions.push_back(tmpInst);
+
+    createShiftOr<false>(MCOperand::CreateExpr(LoExpr), RegNo, SMLoc(),
+                         Instructions);
+  }
+}
+
 void MipsAsmParser::expandMemInst(MCInst &Inst, SMLoc IDLoc,
                                   SmallVectorImpl<MCInst> &Instructions,
                                   bool isLoad, bool isImmOpnd) {
   const MCSymbolRefExpr *SR;
   MCInst TempInst;
   unsigned ImmOffset, HiOffset, LoOffset;
   const MCExpr *ExprOffset;
   unsigned TmpRegNum;

test/MC/Mips/mips-expansions.s

 
 # CHECK: addiu   $4, $zero, 20       # encoding: [0x14,0x00,0x04,0x24]
 # CHECK: lui     $7, 1               # encoding: [0x01,0x00,0x07,0x3c]
 # CHECK: ori     $7, $7, 2           # encoding: [0x02,0x00,0xe7,0x34]
 # CHECK: addiu   $4, $5, 20          # encoding: [0x14,0x00,0xa4,0x24]
 # CHECK: lui     $7, 1               # encoding: [0x01,0x00,0x07,0x3c]
 # CHECK: ori     $7, $7, 2           # encoding: [0x02,0x00,0xe7,0x34]
 # CHECK: addu    $7, $7, $8          # encoding: [0x21,0x38,0xe8,0x00]
+# CHECK: lui $8, %hi(symbol)         # encoding: [A,A,0x08,0x3c]
+                                     #   fixup A - offset: 0, value: symbol@ABS_HI, kind: fixup_Mips_HI16
+# CHECK: ori $8, $8, %lo(symbol)     # encoding: [A,A,0x08,0x35]
+                                     #   fixup A - offset: 0, value: symbol@ABS_LO, kind: fixup_Mips_LO16
+# CHECK: .set    mips64
+# CHECK: lui $8, %highest(symbol)    # encoding: [A,A,0x08,0x3c]
+                                     #   fixup A - offset: 0, value: symbol@HIGHEST, kind: fixup_Mips_HIGHEST
+# CHECK: ori $8, $8, %higher(symbol) # encoding: [A,A,0x08,0x35]
+                                     #   fixup A - offset: 0, value: symbol@HIGHER, kind: fixup_Mips_HIGHER
+# CHECK: dsll    $8, $8, 16          # encoding: [0x38,0x44,0x08,0x00]
+# CHECK: ori $8, $8, %hi(symbol)     # encoding: [A,A,0x08,0x35]
+                                     #   fixup A - offset: 0, value: symbol@ABS_HI, kind: fixup_Mips_HI16
+# CHECK: dsll    $8, $8, 16          # encoding: [0x38,0x44,0x08,0x00]
+# CHECK: ori $8, $8, %lo(symbol)     # encoding: [A,A,0x08,0x35]
+                                     #   fixup A - offset: 0, value: symbol@ABS_LO, kind: fixup_Mips_LO16
+# CHECK: .set    mips32r2
 # CHECK: lui     $10, %hi(symbol)        # encoding: [A,A,0x0a,0x3c]
 # CHECK:                                 #   fixup A - offset: 0, value: symbol@ABS_HI, kind: fixup_Mips_HI16
 # CHECK: addu    $10, $10, $4            # encoding: [0x21,0x50,0x44,0x01]
 # CHECK: lw      $10, %lo(symbol)($10)   # encoding: [A,A,0x4a,0x8d]
 # CHECK:                                 #   fixup A - offset: 0, value: symbol@ABS_LO, kind: fixup_Mips_LO16
 # CHECK: lui     $1, %hi(symbol)         # encoding: [A,A,0x01,0x3c]
 # CHECK:                                 #   fixup A - offset: 0, value: symbol@ABS_HI, kind: fixup_Mips_HI16
 # CHECK: addu    $1, $1, $9              # encoding: [0x21,0x08,0x29,0x00]
# CHECK: sdc1    $f0, %lo(symbol)($1)
     li $6,-2345
     li $7,65538
     li $8, ~7
 
     la $a0, 20
     la $7,65538
     la $a0, 20($a1)
     la $7,65538($8)
+    la  $t0, symbol
+    .set mips64
+    la  $t0, symbol
+    .set mips32r2
 
     .set noat
     lw  $t2, symbol($a0)
     .set at
     sw  $t2, symbol($t1)
 
     lw  $t2, 655483($a0)
     sw  $t2, 123456($t1)
 
     ldc1 $f0, symbol
     sdc1 $f0, symbol