[mips] Reduce number of instructions used for loading a global symbol's value

[atanasyan]

Summary

Now lw/sw $reg, sym+offset pseudo instructions for global symbol sym are lowering into the following three instructions.

lw     $reg, %got(symbol)($gp)
addiu  $reg, $reg, offset
lw/sw  $reg, 0($reg)

It's possible to reduce the number of instructions by taking the offset in account in the final lw/sw command. This patch implements that optimization.

lw     $reg, %got(symbol)($gp)
lw/sw  $reg, offset($reg)

[Petar.Avramovic]

LGTM.

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

if (OffsetOp.isImm()) {
     TOut.emitRRI(Inst.getOpcode(), DstReg, TmpReg, LoOffset, IDLoc, STI);
     return;
   }
 
   if (OffsetOp.isExpr()) {
     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.
-      loadAndAddSymbolAddress(OffsetOp.getExpr(), TmpReg, Mips::NoRegister,
+      MCValue Res;
+      if (!OffsetOp.getExpr()->evaluateAsRelocatable(Res, nullptr, nullptr)) {
+        Error(IDLoc, "expected relocatable expression");
+        return;
+      }
+      if (Res.getSymB() != nullptr) {
+        Error(IDLoc, "expected relocatable expression with only one symbol");
+        return;
+      }
+
+      loadAndAddSymbolAddress(Res.getSymA(), TmpReg, Mips::NoRegister,
                               !ABI.ArePtrs64bit(), IDLoc, Out, STI);
-      TOut.emitRRI(Inst.getOpcode(), DstReg, TmpReg, 0, IDLoc, STI);
+      TOut.emitRRI(Inst.getOpcode(), DstReg, TmpReg, Res.getConstant(), 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)

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

# 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]
+# CHECK-LE:      lw    $8, %got($tmp0)($gp)   # encoding: [A,A,0x88,0x8f]
+# CHECK-LE-NEXT:                              #   fixup A - offset: 0, value: %got($tmp0), kind: fixup_Mips_GOT
+# CHECK-LE-NEXT: addiu $8, $8, %lo($tmp0)     # encoding: [A,A,0x08,0x25]
+# CHECK-LE-NEXT:                              #   fixup A - offset: 0, value: %lo($tmp0), kind: fixup_Mips_LO16
+# CHECK-LE-NEXT: lw    $8, 8($8)              # encoding: [0x08,0x00,0x08,0x8d]
   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]
+# CHECK-LE:      lw    $1, %got($tmp0)($gp)   # encoding: [A,A,0x81,0x8f]
+# CHECK-LE-NEXT:                              #   fixup A - offset: 0, value: %got($tmp0), kind: fixup_Mips_GOT
+# CHECK-LE-NEXT: addiu $1, $1, %lo($tmp0)     # encoding: [A,A,0x21,0x24]
+# CHECK-LE-NEXT:                              #   fixup A - offset: 0, value: %lo($tmp0), kind: fixup_Mips_LO16
+# CHECK-LE-NEXT: sw    $8, 8($1)              # encoding: [0x08,0x00,0x28,0xac]
 
   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      $8, %got(symbol)($gp)     # encoding: [A,A,0x88,0x8f]
-# CHECK-LE:                                   #   fixup A - offset: 0, value: %got(symbol), 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]
+# CHECK-LE:      lw $8, %got(symbol)($gp)     # encoding: [A,A,0x88,0x8f]
+# CHECK-LE-NEXT:                              #   fixup A - offset: 0, value: %got(symbol), kind: fixup_Mips_GOT
+# CHECK-LE-NEXT: lw $8, 8($8)                 # encoding: [0x08,0x00,0x08,0x8d]
   sw $8, symbol+8
-# 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: addiu   $1, $1, 8                 # encoding: [0x08,0x00,0x21,0x24]
-# CHECK-LE: sw      $8, 0($1)                 # encoding: [0x00,0x00,0x28,0xac]
+# CHECK-LE:      lw $1, %got(symbol)($gp)     # encoding: [A,A,0x81,0x8f]
+# CHECK-LE-NEXT:                              #   fixup A - offset: 0, value: %got(symbol), kind: fixup_Mips_GOT
+# CHECK-LE-NEXT: sw $8, 8($1)                 # encoding: [0x08,0x00,0x28,0xac]
 
   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

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

 # 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]
+# CHECK:      ld $8, %got_disp(sym)($gp)    # encoding: [A,A,0x88,0xdf]
+# CHECK-NEXT:                               #   fixup A - offset: 0, value: %got_disp(sym), kind: fixup_Mips_GOT_DISP
+# CHECK-NEXT: lw $8, 8($8)                  # encoding: [0x08,0x00,0x08,0x8d]
   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]
+# CHECK:      ld $1, %got_disp(sym)($gp)    # encoding: [A,A,0x81,0xdf]
+# CHECK-NEXT:                               #   fixup A - offset: 0, value: %got_disp(sym), kind: fixup_Mips_GOT_DISP
+# CHECK-NEXT: sw $8, 8($1)                  # encoding: [0x08,0x00,0x28,0xac]
 
   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]
+# CHECK:      ld $8, %got_disp(symbol)($gp) # encoding: [A,A,0x88,0xdf]
+# CHECK-NEXT:                               #   fixup A - offset: 0, value: %got_disp(symbol), kind: fixup_Mips_GOT_DISP
+# CHECK-NEXT: lw $8, 8($8)                  # encoding: [0x08,0x00,0x08,0x8d]
   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]
+# CHECK:      ld $1, %got_disp(symbol)($gp) # encoding: [A,A,0x81,0xdf]
+# CHECK-NEXT:                               #   fixup A - offset: 0, value: %got_disp(symbol), kind: fixup_Mips_GOT_DISP
+# CHECK-NEXT: sw $8, 8($1)                  # encoding: [0x08,0x00,0x28,0xac]
 
   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]