[mips] Fix lowering load/store instruction in PIC case

[atanasyan]

Summary

If an operand of the lw/sw instructions is a symbol, these instructions incorrectly lowered using not-position-independent chain of commands. For PIC code we should use lw/addiu instructions with the R_MIPS_GOT16 and R_MIPS_LO16 relocations respectively. Instead of that LLVM generates position dependent code with the R_MIPS_HI16 and R_MIPS_LO16 relocations.

This patch provides a fix for the bug by handling PIC case separately in the MipsAsmParser::expandMemInst. The main idea is to generate a chain of PIC instructions to load a symbol address into a register and then load the address content.

The fix is not optimal and does not fix all PIC-related problems. This is a task for subsequent patches.

[Petar.Avramovic]

LGTM.

[atanasyan]

Thanks.

llvm/lib/Target/Mips/AsmParser/MipsAsmParser.cpp

if (IsLargeOffset) {
                         IDLoc, Out, STI))
         return;
     }
 
     if (BaseReg != Mips::ZERO && BaseReg != Mips::ZERO_64)
       TOut.emitRRR(isGP64bit() ? Mips::DADDu : Mips::ADDu, TmpReg, TmpReg,
                    BaseReg, IDLoc, STI);
     TOut.emitRRI(Inst.getOpcode(), DstReg, TmpReg, LoOffset, IDLoc, STI);
-  } else {
-    assert(OffsetOp.isExpr() && "expected expression operand kind");
+    return;
+  }
+
+  if (inPicMode()) {
+    // FIXME:
+    // a) Fix lw/sw $reg, symbol($reg) instruction expanding.
+    // b) If expression includes offset (sym + number), do not
+    //    encode the offset into a relocation. Take it in account
+    //    in the last load/store instruction.
+    // c) Check that immediates of R_MIPS_GOT16/R_MIPS_LO16 relocations
+    //    do not exceed 16-bit.
+    // d) Use R_MIPS_GOT_PAGE/R_MIPS_GOT_OFST relocations instead
+    //    of R_MIPS_GOT_DISP in appropriate cases to reduce number
+    //    of GOT entries.
+    expandLoadAddress(TmpReg, Mips::NoRegister, OffsetOp, !ABI.ArePtrs64bit(),
+                      IDLoc, Out, STI);
+    TOut.emitRRI(Inst.getOpcode(), DstReg, TmpReg, 0, IDLoc, STI);
+  } else {
     const MCExpr *ExprOffset = OffsetOp.getExpr();
     MCOperand LoOperand = MCOperand::createExpr(
         MipsMCExpr::create(MipsMCExpr::MEK_LO, ExprOffset, getContext()));
     MCOperand HiOperand = MCOperand::createExpr(
         MipsMCExpr::create(MipsMCExpr::MEK_HI, ExprOffset, getContext()));
 
     if (IsLoad)
       TOut.emitLoadWithSymOffset(Inst.getOpcode(), DstReg, BaseReg, HiOperand,

llvm/test/MC/Mips/mips-expansions.s

 # CHECK-LE: lhu     $4, -32768($4)
 
   lhu  $4, 0x20004($3)
 # CHECK-LE: lui     $4, 2
 # CHECK-LE: addu    $4, $4, $3
 # CHECK-LE: lhu     $4, 4($4)
 
 # LW/SW and LDC1/SDC1 of symbol address, done by MipsAsmParser::expandMemInst():
+# NON-PIC code
   .set noat
   lw $10, symbol($4)
 # CHECK-LE: lui     $10, %hi(symbol)        # encoding: [A,A,0x0a,0x3c]
 # CHECK-LE:                                 #   fixup A - offset: 0, value: %hi(symbol), kind: fixup_Mips_HI16
 # CHECK-LE: addu    $10, $10, $4            # encoding: [0x21,0x50,0x44,0x01]
 # CHECK-LE: lw      $10, %lo(symbol)($10)   # encoding: [A,A,0x4a,0x8d]
 # CHECK-LE:                                 #   fixup A - offset: 0, value: %lo(symbol), kind: fixup_Mips_LO16
   .set at
# CHECK-LE:                                 #   fixup A - offset: 0, value: %lo(symbol), kind: fixup_Mips_LO16
 
   ldc1 $f0, symbol
 # CHECK-LE: lui     $1, %hi(symbol)
 # CHECK-LE: ldc1    $f0, %lo(symbol)($1)
   sdc1 $f0, symbol
 # CHECK-LE: lui     $1, %hi(symbol)
 # CHECK-LE: sdc1    $f0, %lo(symbol)($1)
 
+# PIC code
+  .option pic2
+  .set noat
+  lw $10, symbol($4)
+# CHECK-LE: lw      $10, %got(symbol)($gp)    # encoding: [A,A,0x8a,0x8f]
+# CHECK-LE:                                   #   fixup A - offset: 0, value: %got(symbol), kind: fixup_Mips_GOT
+# CHECK-LE-FIXME: addu    $10, $10, $4        # encoding: [0x21,0x50,0x44,0x01]
+# CHECK-LE: lw      $10, 0($10)               # encoding: [0x00,0x00,0x4a,0x8d]
+  .set at
+  sw $10, symbol($9)
+# CHECK-LE: lw      $1, %got(symbol)($gp)     # encoding: [A,A,0x81,0x8f]
+# CHECK-LE:                                   #   fixup A - offset: 0, value: %got(symbol), kind: fixup_Mips_GOT
+# CHECK-LE-FIXME: addu    $1, $1, $9          # encoding: [0x21,0x08,0x29,0x00]
+# CHECK-LE: sw      $10, 0($1)                # encoding: [0x00,0x00,0x2a,0xac]
+
+  lw $8, 1f+8
+# CHECK-LE: lw      $8, %got(($tmp0)+8)($gp)  # encoding: [A,A,0x88,0x8f]
+# CHECK-LE:                                   #   fixup A - offset: 0, value: %got(($tmp0)+8), kind: fixup_Mips_GOT
+# CHECK-LE: addiu   $8, $8, %lo(($tmp0)+8)    # encoding: [A,A,0x08,0x25]
+# CHECK-LE:                                   #   fixup A - offset: 0, value: %lo(($tmp0)+8), kind: fixup_Mips_LO16
+# CHECK-LE: lw      $8, 0($8)                 # encoding: [0x00,0x00,0x08,0x8d]
+  sw $8, 1f+8
+# CHECK-LE: lw      $1, %got(($tmp0)+8)($gp)  # encoding: [A,A,0x81,0x8f]
+# CHECK-LE:                                   #   fixup A - offset: 0, value: %got(($tmp0)+8), kind: fixup_Mips_GOT
+# CHECK-LE: addiu   $1, $1, %lo(($tmp0)+8)    # encoding: [A,A,0x21,0x24]
+# CHECK-LE:                                   #   fixup A - offset: 0, value: %lo(($tmp0)+8), kind: fixup_Mips_LO16
+# CHECK-LE: sw      $8, 0($1)                 # encoding: [0x00,0x00,0x28,0xac]
+
+  lw $10, 655483($4)
+# CHECK-LE: lui     $10, 10                   # encoding: [0x0a,0x00,0x0a,0x3c]
+# CHECK-LE: addu    $10, $10, $4              # encoding: [0x21,0x50,0x44,0x01]
+# CHECK-LE: lw      $10, 123($10)             # encoding: [0x7b,0x00,0x4a,0x8d]
+  sw $10, 123456($9)
+# CHECK-LE: lui     $1, 2                     # encoding: [0x02,0x00,0x01,0x3c]
+# CHECK-LE: addu    $1, $1, $9                # encoding: [0x21,0x08,0x29,0x00]
+# CHECK-LE: sw      $10, -7616($1)            # encoding: [0x40,0xe2,0x2a,0xac]
+
+  lw $8, symbol+8
+# CHECK-LE: lw      $8, %got(symbol+8)($gp)   # encoding: [A,A,0x88,0x8f]
+# CHECK-LE:                                   #   fixup A - offset: 0, value: %got(symbol+8), kind: fixup_Mips_GOT
+# CHECK-LE: addiu   $8, $8, 8                 # encoding: [0x08,0x00,0x08,0x25]
+# CHECK-LE: lw      $8, 0($8)                 # encoding: [0x00,0x00,0x08,0x8d]
+  sw $8, symbol+8
+# CHECK-LE: lw      $1, %got(symbol+8)($gp)   # encoding: [A,A,0x81,0x8f]
+# CHECK-LE:                                   #   fixup A - offset: 0, value: %got(symbol+8), kind: fixup_Mips_GOT
+# CHECK-LE: addiu   $1, $1, 8                 # encoding: [0x08,0x00,0x21,0x24]
+# CHECK-LE: sw      $8, 0($1)                 # encoding: [0x00,0x00,0x28,0xac]
+
+  ldc1 $f0, symbol
+# CHECK-LE: lw      $1, %got(symbol)($gp)     # encoding: [A,A,0x81,0x8f]
+# CHECK-LE:                                   #   fixup A - offset: 0, value: %got(symbol), kind: fixup_Mips_GOT
+# CHECK-LE: ldc1    $f0, 0($1)                # encoding: [0x00,0x00,0x20,0xd4]
+  sdc1 $f0, symbol
+# CHECK-LE: lw      $1, %got(symbol)($gp)     # encoding: [A,A,0x81,0x8f]
+# CHECK-LE:                                   #   fixup A - offset: 0, value: %got(symbol), kind: fixup_Mips_GOT
+# CHECK-LE: sdc1    $f0, 0($1)                # encoding: [0x00,0x00,0x20,0xf4]
+  .option pic0
+
 # Test BNE with an immediate as the 2nd operand.
   bne $2, 0, 1332
 # CHECK-LE: bnez  $2, 1332          # encoding: [0x4d,0x01,0x40,0x14]
 # CHECK-LE: nop                     # encoding: [0x00,0x00,0x00,0x00]
 
   bne $2, 123, 1332
 # CHECK-LE: addiu $1, $zero, 123    # encoding: [0x7b,0x00,0x01,0x24]
 # CHECK-LE: bne   $2, $1, 1332      # encoding: [0x4d,0x01,0x41,0x14]

llvm/test/MC/Mips/mips64-expansions.s

# CHECK-NEXT: lhu     $4, -32764($4)
     lhu $4,0x1800180018004($3)
 # CHECK:      lui     $4, 1
 # CHECK-NEXT: ori     $4, $4, 32769
 # CHECK-NEXT: dsll    $4, $4, 16
 # CHECK-NEXT: ori     $4, $4, 32770
 # CHECK-NEXT: dsll    $4, $4, 16
 # CHECK-NEXT: daddu   $4, $4, $3
 # CHECK-NEXT: lhu     $4, -32764($4)
+
+# LW/SW and LDC1/SDC1 of symbol address, done by MipsAsmParser::expandMemInst():
+  .option pic2
+  lw $10, symbol($4)
+# CHECK: ld      $10, %got_disp(symbol)($gp) # encoding: [A,A,0x8a,0xdf]
+# CHECK:                                    #   fixup A - offset: 0, value: %got_disp(symbol), kind: fixup_Mips_GOT_DISP
+# CHECK-FIXME: daddu   $10, $10, $4         # encoding: [0x2d,0x50,0x44,0x01]
+# CHECK: lw      $10, 0($10)                # encoding: [0x00,0x00,0x4a,0x8d]
+  sw $10, symbol($9)
+# CHECK: ld      $1, %got_disp(symbol)($gp) # encoding: [A,A,0x81,0xdf]
+# CHECK:                                    #   fixup A - offset: 0, value: %got_disp(symbol), kind: fixup_Mips_GOT_DISP
+# CHECK-FIXME: daddu    $1, $1, $9          # encoding: [0x2d,0x08,0x29,0x00]
+# CHECK: sw      $10, 0($1)                 # encoding: [0x00,0x00,0x2a,0xac]
+
+  lw $8, sym+8
+# CHECK: ld      $8, %got_disp(sym)($gp)    # encoding: [A,A,0x88,0xdf]
+# CHECK:                                    #   fixup A - offset: 0, value: %got_disp(sym), kind: fixup_Mips_GOT_DISP
+# CHECK: daddiu  $8, $8, 8                  # encoding: [0x08,0x00,0x08,0x65]
+# CHECK: lw      $8, 0($8)                  # encoding: [0x00,0x00,0x08,0x8d]
+  sw $8, sym+8
+# CHECK: ld      $1, %got_disp(sym)($gp) # encoding: [A,A,0x81,0xdf]
+# CHECK:                                    #   fixup A - offset: 0, value: %got_disp(sym), kind: fixup_Mips_GOT_DISP
+# CHECK: daddiu  $1, $1, 8                  # encoding: [0x08,0x00,0x21,0x64]
+# CHECK: sw      $8, 0($1)                  # encoding: [0x00,0x00,0x28,0xac]
+
+  lw $10, 655483($4)
+# CHECK: lui     $10, 10                    # encoding: [0x0a,0x00,0x0a,0x3c]
+# CHECK: daddu   $10, $10, $4               # encoding: [0x2d,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: daddu   $1, $1, $9                 # encoding: [0x2d,0x08,0x29,0x00]
+# CHECK: sw      $10, -7616($1)             # encoding: [0x40,0xe2,0x2a,0xac]
+
+  lw $8, symbol+8
+# CHECK: ld      $8, %got_disp(symbol)($gp) # encoding: [A,A,0x88,0xdf]
+# CHECK:                                    #   fixup A - offset: 0, value: %got_disp(symbol), kind: fixup_Mips_GOT_DISP
+# CHECK: daddiu  $8, $8, 8                  # encoding: [0x08,0x00,0x08,0x65]
+# CHECK: lw      $8, 0($8)                  # encoding: [0x00,0x00,0x08,0x8d]
+  sw $8, symbol+8
+# CHECK: ld      $1, %got_disp(symbol)($gp) # encoding: [A,A,0x81,0xdf]
+# CHECK:                                    #   fixup A - offset: 0, value: %got_disp(symbol), kind: fixup_Mips_GOT_DISP
+# CHECK: daddiu  $1, $1, 8                  # encoding: [0x08,0x00,0x21,0x64]
+# CHECK: sw      $8, 0($1)                  # encoding: [0x00,0x00,0x28,0xac]
+
+  ldc1 $f0, symbol
+# CHECK: ld      $1, %got_disp(symbol)($gp) # encoding: [A,A,0x81,0xdf]
+# CHECK:                                    #   fixup A - offset: 0, value: %got_disp(symbol), kind: fixup_Mips_GOT_DISP
+# CHECK: ldc1    $f0, 0($1)                 # encoding: [0x00,0x00,0x20,0xd4]
+  sdc1 $f0, symbol
+# CHECK: ld      $1, %got_disp(symbol)($gp) # encoding: [A,A,0x81,0xdf]
+# CHECK:                                    #   fixup A - offset: 0, value: %got_disp(symbol), kind: fixup_Mips_GOT_DISP
+# CHECK: sdc1    $f0, 0($1)                 # encoding: [0x00,0x00,0x20,0xf4]