[mips] [IAS] Fix LW with relative label operands.

[tomatabacu]

Summary

Previously, MCSymbolRefExpr::create() was called with a StringRef of the symbol
name, which it would then search for in the Symbols StringMap (from MCContext).

However, relative labels (which are temporary symbols) are apparently not stored
in the Symbols StringMap, so we end up creating a new {$,.L}tmp symbol
({$,.L}tmp00, {$,.L}tmp10 etc.) each time we create an MCSymbolRefExpr by
passing in the symbol name as a StringRef.

Fortunately, there is a version of MCSymbolRefExpr::create() which takes an
MCSymbol* and we already have an MCSymbol* at that point, so we can just pass
that in instead of the StringRef.

I also removed the local StringRef calls to MCSymbolRefExpr::create() from
expandMemInst(), as those cases can be handled by evaluateRelocExpr() anyway.

[tomatabacu]

Rebased (for Sean Bruno's convenience).

[dsanders]

The overall change LGTM. I think it probably ought to be committed in two steps but the patch is small enough that I don't mind either way. If you do split it, the first step would drop the .getName() calls and the second step would fold the remaining code into evaluateRelocExpr().

lib/Target/Mips/AsmParser/MipsAsmParser.cpp

if (ImmValue == 0) {
     Instructions.push_back(BranchInst);
   }
   return false;
 }
 
 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;
   // 1st operand is either the source or destination register.
   assert(Inst.getOperand(0).isReg() && "expected register operand kind");
   unsigned RegOpNum = Inst.getOperand(0).getReg();
   // 2nd operand is the base register.
if (!TmpRegNum)
       return;
   }
 
   TempInst.setOpcode(Mips::LUi);
   TempInst.addOperand(MCOperand::createReg(TmpRegNum));
   if (isImmOpnd)
     TempInst.addOperand(MCOperand::createImm(HiOffset));
   else {
-    if (ExprOffset->getKind() == MCExpr::SymbolRef) {
-      SR = static_cast<const MCSymbolRefExpr *>(ExprOffset);
-      const MCSymbolRefExpr *HiExpr = MCSymbolRefExpr::create(
-          SR->getSymbol().getName(), MCSymbolRefExpr::VK_Mips_ABS_HI,
-          getContext());
-      TempInst.addOperand(MCOperand::createExpr(HiExpr));
-    } else {
-      const MCExpr *HiExpr = evaluateRelocExpr(ExprOffset, "hi");
-      TempInst.addOperand(MCOperand::createExpr(HiExpr));
-    }
-  }
   // Add the instruction to the list.
   Instructions.push_back(TempInst);
   // Prepare TempInst for next instruction.
   TempInst.clear();
   // Add temp register to base.
   if (BaseRegNum != Mips::ZERO) {
     TempInst.setOpcode(Mips::ADDu);
     TempInst.addOperand(MCOperand::createReg(TmpRegNum));
     TempInst.addOperand(MCOperand::createReg(TmpRegNum));
     TempInst.addOperand(MCOperand::createReg(BaseRegNum));
     Instructions.push_back(TempInst);
     TempInst.clear();
   }
   // And finally, create original instruction with low part
   // of offset and new base.
   TempInst.setOpcode(Inst.getOpcode());
   TempInst.addOperand(MCOperand::createReg(RegOpNum));
   TempInst.addOperand(MCOperand::createReg(TmpRegNum));
   if (isImmOpnd)
     TempInst.addOperand(MCOperand::createImm(LoOffset));
   else {
-    if (ExprOffset->getKind() == MCExpr::SymbolRef) {
-      const MCSymbolRefExpr *LoExpr = MCSymbolRefExpr::create(
-          SR->getSymbol().getName(), MCSymbolRefExpr::VK_Mips_ABS_LO,
-          getContext());
-      TempInst.addOperand(MCOperand::createExpr(LoExpr));
-    } else {
-      const MCExpr *LoExpr = evaluateRelocExpr(ExprOffset, "lo");
-      TempInst.addOperand(MCOperand::createExpr(LoExpr));
-    }
-  }
   Instructions.push_back(TempInst);
   TempInst.clear();
 }
 
 bool
 MipsAsmParser::expandLoadStoreMultiple(MCInst &Inst, SMLoc IDLoc,
                                        SmallVectorImpl<MCInst> &Instructions) {
   unsigned OpNum = Inst.getNumOperands();
if (const MCConstantExpr *MCE = dyn_cast<MCConstantExpr>(Expr)) {
     default:
       report_fatal_error("unsupported reloc value");
     }
     return MCConstantExpr::create(Val, getContext());
   }
 
   if (const MCSymbolRefExpr *MSRE = dyn_cast<MCSymbolRefExpr>(Expr)) {
     // It's a symbol, create a symbolic expression from the symbol.
-    StringRef Symbol = MSRE->getSymbol().getName();
+    const MCSymbol *Symbol = &MSRE->getSymbol();
     MCSymbolRefExpr::VariantKind VK = getVariantKind(RelocStr);
     Res = MCSymbolRefExpr::create(Symbol, VK, getContext());
     return Res;
   }
 
   if (const MCBinaryExpr *BE = dyn_cast<MCBinaryExpr>(Expr)) {
     MCSymbolRefExpr::VariantKind VK = getVariantKind(RelocStr);
 

test/MC/Mips/mips-expansions.s

# CHECK:                                 #   fixup A - offset: 0, value: symbol@ABS_LO, kind: fixup_Mips_LO16
   .set at
   sw $10, symbol($9)
 # 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: sw      $10, %lo(symbol)($1)    # encoding: [A,A,0x2a,0xac]
 # CHECK:                                 #   fixup A - offset: 0, value: symbol@ABS_LO, kind: fixup_Mips_LO16
 
+  lw $8, 1f
+# CHECK: lui $8, %hi($tmp0)              # encoding: [A,A,0x08,0x3c]
+# CHECK:                                 #   fixup A - offset: 0, value: ($tmp0)@ABS_HI, kind: fixup_Mips_HI16
+# CHECK: lw  $8, %lo($tmp0)($8)          # encoding: [A,A,0x08,0x8d]
+# CHECK:                                 #   fixup A - offset: 0, value: ($tmp0)@ABS_LO, kind: fixup_Mips_LO16
+
   lw $10, 655483($4)
 # CHECK: lui     $10, 10                 # encoding: [0x0a,0x00,0x0a,0x3c]
 # CHECK: addu    $10, $10, $4            # encoding: [0x21,0x50,0x44,0x01]
 # CHECK: lw      $10, 123($10)           # encoding: [0x7b,0x00,0x4a,0x8d]
   sw $10, 123456($9)
 # CHECK: lui     $1, 2                   # encoding: [0x02,0x00,0x01,0x3c]
 # CHECK: addu    $1, $1, $9              # encoding: [0x21,0x08,0x29,0x00]
 # CHECK: sw      $10, 57920($1)          # encoding: [0x40,0xe2,0x2a,0xac]

 # CHECK: addiu $1, $zero, -8     # encoding: [0xf8,0xff,0x01,0x24]
 # CHECK: beq   $2, $1, 1332      # encoding: [0x4d,0x01,0x41,0x10]
 # CHECK: nop                     # encoding: [0x00,0x00,0x00,0x00]
 
   beq $2, 0x10000, 1332
 # CHECK: lui   $1, 1             # encoding: [0x01,0x00,0x01,0x3c]
 # CHECK: beq   $2, $1, 1332      # encoding: [0x4d,0x01,0x41,0x10]
 # CHECK: nop                     # encoding: [0x00,0x00,0x00,0x00]
+
+1:
+  add $4, $4, $4