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      1 //===-- PPCJITInfo.cpp - Implement the JIT interfaces for the PowerPC -----===//
      2 //
      3 //                     The LLVM Compiler Infrastructure
      4 //
      5 // This file is distributed under the University of Illinois Open Source
      6 // License. See LICENSE.TXT for details.
      7 //
      8 //===----------------------------------------------------------------------===//
      9 //
     10 // This file implements the JIT interfaces for the 32-bit PowerPC target.
     11 //
     12 //===----------------------------------------------------------------------===//
     13 
     14 #define DEBUG_TYPE "jit"
     15 #include "PPCJITInfo.h"
     16 #include "PPCRelocations.h"
     17 #include "PPCTargetMachine.h"
     18 #include "llvm/Function.h"
     19 #include "llvm/Support/Memory.h"
     20 #include "llvm/Support/Debug.h"
     21 #include "llvm/Support/ErrorHandling.h"
     22 #include "llvm/Support/raw_ostream.h"
     23 using namespace llvm;
     24 
     25 static TargetJITInfo::JITCompilerFn JITCompilerFunction;
     26 
     27 #define BUILD_ADDIS(RD,RS,IMM16) \
     28   ((15 << 26) | ((RD) << 21) | ((RS) << 16) | ((IMM16) & 65535))
     29 #define BUILD_ORI(RD,RS,UIMM16) \
     30   ((24 << 26) | ((RS) << 21) | ((RD) << 16) | ((UIMM16) & 65535))
     31 #define BUILD_ORIS(RD,RS,UIMM16) \
     32   ((25 << 26) | ((RS) << 21) | ((RD) << 16) | ((UIMM16) & 65535))
     33 #define BUILD_RLDICR(RD,RS,SH,ME) \
     34   ((30 << 26) | ((RS) << 21) | ((RD) << 16) | (((SH) & 31) << 11) | \
     35    (((ME) & 63) << 6) | (1 << 2) | ((((SH) >> 5) & 1) << 1))
     36 #define BUILD_MTSPR(RS,SPR)      \
     37   ((31 << 26) | ((RS) << 21) | ((SPR) << 16) | (467 << 1))
     38 #define BUILD_BCCTRx(BO,BI,LINK) \
     39   ((19 << 26) | ((BO) << 21) | ((BI) << 16) | (528 << 1) | ((LINK) & 1))
     40 #define BUILD_B(TARGET, LINK) \
     41   ((18 << 26) | (((TARGET) & 0x00FFFFFF) << 2) | ((LINK) & 1))
     42 
     43 // Pseudo-ops
     44 #define BUILD_LIS(RD,IMM16)    BUILD_ADDIS(RD,0,IMM16)
     45 #define BUILD_SLDI(RD,RS,IMM6) BUILD_RLDICR(RD,RS,IMM6,63-IMM6)
     46 #define BUILD_MTCTR(RS)        BUILD_MTSPR(RS,9)
     47 #define BUILD_BCTR(LINK)       BUILD_BCCTRx(20,0,LINK)
     48 
     49 static void EmitBranchToAt(uint64_t At, uint64_t To, bool isCall, bool is64Bit){
     50   intptr_t Offset = ((intptr_t)To - (intptr_t)At) >> 2;
     51   unsigned *AtI = (unsigned*)(intptr_t)At;
     52 
     53   if (Offset >= -(1 << 23) && Offset < (1 << 23)) {   // In range?
     54     AtI[0] = BUILD_B(Offset, isCall);     // b/bl target
     55   } else if (!is64Bit) {
     56     AtI[0] = BUILD_LIS(12, To >> 16);     // lis r12, hi16(address)
     57     AtI[1] = BUILD_ORI(12, 12, To);       // ori r12, r12, lo16(address)
     58     AtI[2] = BUILD_MTCTR(12);             // mtctr r12
     59     AtI[3] = BUILD_BCTR(isCall);          // bctr/bctrl
     60   } else {
     61     AtI[0] = BUILD_LIS(12, To >> 48);      // lis r12, hi16(address)
     62     AtI[1] = BUILD_ORI(12, 12, To >> 32);  // ori r12, r12, lo16(address)
     63     AtI[2] = BUILD_SLDI(12, 12, 32);       // sldi r12, r12, 32
     64     AtI[3] = BUILD_ORIS(12, 12, To >> 16); // oris r12, r12, hi16(address)
     65     AtI[4] = BUILD_ORI(12, 12, To);        // ori r12, r12, lo16(address)
     66     AtI[5] = BUILD_MTCTR(12);              // mtctr r12
     67     AtI[6] = BUILD_BCTR(isCall);           // bctr/bctrl
     68   }
     69 }
     70 
     71 extern "C" void PPC32CompilationCallback();
     72 extern "C" void PPC64CompilationCallback();
     73 
     74 #if (defined(__POWERPC__) || defined (__ppc__) || defined(_POWER)) && \
     75     !(defined(__ppc64__) || defined(__FreeBSD__))
     76 // CompilationCallback stub - We can't use a C function with inline assembly in
     77 // it, because we the prolog/epilog inserted by GCC won't work for us.  Instead,
     78 // write our own wrapper, which does things our way, so we have complete control
     79 // over register saving and restoring.
     80 asm(
     81     ".text\n"
     82     ".align 2\n"
     83     ".globl _PPC32CompilationCallback\n"
     84 "_PPC32CompilationCallback:\n"
     85     // Make space for 8 ints r[3-10] and 13 doubles f[1-13] and the
     86     // FIXME: need to save v[0-19] for altivec?
     87     // FIXME: could shrink frame
     88     // Set up a proper stack frame
     89     // FIXME Layout
     90     //   PowerPC32 ABI linkage    -  24 bytes
     91     //                 parameters -  32 bytes
     92     //   13 double registers      - 104 bytes
     93     //   8 int registers          -  32 bytes
     94     "mflr r0\n"
     95     "stw r0,  8(r1)\n"
     96     "stwu r1, -208(r1)\n"
     97     // Save all int arg registers
     98     "stw r10, 204(r1)\n"    "stw r9,  200(r1)\n"
     99     "stw r8,  196(r1)\n"    "stw r7,  192(r1)\n"
    100     "stw r6,  188(r1)\n"    "stw r5,  184(r1)\n"
    101     "stw r4,  180(r1)\n"    "stw r3,  176(r1)\n"
    102     // Save all call-clobbered FP regs.
    103     "stfd f13, 168(r1)\n"   "stfd f12, 160(r1)\n"
    104     "stfd f11, 152(r1)\n"   "stfd f10, 144(r1)\n"
    105     "stfd f9,  136(r1)\n"   "stfd f8,  128(r1)\n"
    106     "stfd f7,  120(r1)\n"   "stfd f6,  112(r1)\n"
    107     "stfd f5,  104(r1)\n"   "stfd f4,   96(r1)\n"
    108     "stfd f3,   88(r1)\n"   "stfd f2,   80(r1)\n"
    109     "stfd f1,   72(r1)\n"
    110     // Arguments to Compilation Callback:
    111     // r3 - our lr (address of the call instruction in stub plus 4)
    112     // r4 - stub's lr (address of instruction that called the stub plus 4)
    113     // r5 - is64Bit - always 0.
    114     "mr   r3, r0\n"
    115     "lwz  r2, 208(r1)\n" // stub's frame
    116     "lwz  r4, 8(r2)\n" // stub's lr
    117     "li   r5, 0\n"       // 0 == 32 bit
    118     "bl _PPCCompilationCallbackC\n"
    119     "mtctr r3\n"
    120     // Restore all int arg registers
    121     "lwz r10, 204(r1)\n"    "lwz r9,  200(r1)\n"
    122     "lwz r8,  196(r1)\n"    "lwz r7,  192(r1)\n"
    123     "lwz r6,  188(r1)\n"    "lwz r5,  184(r1)\n"
    124     "lwz r4,  180(r1)\n"    "lwz r3,  176(r1)\n"
    125     // Restore all FP arg registers
    126     "lfd f13, 168(r1)\n"    "lfd f12, 160(r1)\n"
    127     "lfd f11, 152(r1)\n"    "lfd f10, 144(r1)\n"
    128     "lfd f9,  136(r1)\n"    "lfd f8,  128(r1)\n"
    129     "lfd f7,  120(r1)\n"    "lfd f6,  112(r1)\n"
    130     "lfd f5,  104(r1)\n"    "lfd f4,   96(r1)\n"
    131     "lfd f3,   88(r1)\n"    "lfd f2,   80(r1)\n"
    132     "lfd f1,   72(r1)\n"
    133     // Pop 3 frames off the stack and branch to target
    134     "lwz  r1, 208(r1)\n"
    135     "lwz  r2, 8(r1)\n"
    136     "mtlr r2\n"
    137     "bctr\n"
    138     );
    139 
    140 #elif defined(__PPC__) && !defined(__ppc64__)
    141 // Linux & FreeBSD / PPC 32 support
    142 
    143 // CompilationCallback stub - We can't use a C function with inline assembly in
    144 // it, because we the prolog/epilog inserted by GCC won't work for us.  Instead,
    145 // write our own wrapper, which does things our way, so we have complete control
    146 // over register saving and restoring.
    147 asm(
    148     ".text\n"
    149     ".align 2\n"
    150     ".globl PPC32CompilationCallback\n"
    151 "PPC32CompilationCallback:\n"
    152     // Make space for 8 ints r[3-10] and 8 doubles f[1-8] and the
    153     // FIXME: need to save v[0-19] for altivec?
    154     // FIXME: could shrink frame
    155     // Set up a proper stack frame
    156     // FIXME Layout
    157     //   8 double registers       -  64 bytes
    158     //   8 int registers          -  32 bytes
    159     "mflr 0\n"
    160     "stw 0,  4(1)\n"
    161     "stwu 1, -104(1)\n"
    162     // Save all int arg registers
    163     "stw 10, 100(1)\n"   "stw 9,  96(1)\n"
    164     "stw 8,  92(1)\n"    "stw 7,  88(1)\n"
    165     "stw 6,  84(1)\n"    "stw 5,  80(1)\n"
    166     "stw 4,  76(1)\n"    "stw 3,  72(1)\n"
    167     // Save all call-clobbered FP regs.
    168     "stfd 8,  64(1)\n"
    169     "stfd 7,  56(1)\n"   "stfd 6,  48(1)\n"
    170     "stfd 5,  40(1)\n"   "stfd 4,  32(1)\n"
    171     "stfd 3,  24(1)\n"   "stfd 2,  16(1)\n"
    172     "stfd 1,  8(1)\n"
    173     // Arguments to Compilation Callback:
    174     // r3 - our lr (address of the call instruction in stub plus 4)
    175     // r4 - stub's lr (address of instruction that called the stub plus 4)
    176     // r5 - is64Bit - always 0.
    177     "mr   3, 0\n"
    178     "lwz  5, 104(1)\n" // stub's frame
    179     "lwz  4, 4(5)\n" // stub's lr
    180     "li   5, 0\n"       // 0 == 32 bit
    181     "bl PPCCompilationCallbackC\n"
    182     "mtctr 3\n"
    183     // Restore all int arg registers
    184     "lwz 10, 100(1)\n"   "lwz 9,  96(1)\n"
    185     "lwz 8,  92(1)\n"    "lwz 7,  88(1)\n"
    186     "lwz 6,  84(1)\n"    "lwz 5,  80(1)\n"
    187     "lwz 4,  76(1)\n"    "lwz 3,  72(1)\n"
    188     // Restore all FP arg registers
    189     "lfd 8,  64(1)\n"
    190     "lfd 7,  56(1)\n"    "lfd 6,  48(1)\n"
    191     "lfd 5,  40(1)\n"    "lfd 4,  32(1)\n"
    192     "lfd 3,  24(1)\n"    "lfd 2,  16(1)\n"
    193     "lfd 1,  8(1)\n"
    194     // Pop 3 frames off the stack and branch to target
    195     "lwz  1, 104(1)\n"
    196     "lwz  0, 4(1)\n"
    197     "mtlr 0\n"
    198     "bctr\n"
    199     );
    200 #else
    201 void PPC32CompilationCallback() {
    202   llvm_unreachable("This is not a power pc, you can't execute this!");
    203 }
    204 #endif
    205 
    206 #if (defined(__POWERPC__) || defined (__ppc__) || defined(_POWER)) && \
    207     defined(__ppc64__)
    208 #ifdef __ELF__
    209 asm(
    210     ".text\n"
    211     ".align 2\n"
    212     ".globl PPC64CompilationCallback\n"
    213     ".section \".opd\",\"aw\"\n"
    214     ".align 3\n"
    215 "PPC64CompilationCallback:\n"
    216     ".quad .L.PPC64CompilationCallback,.TOC.@tocbase,0\n"
    217     ".size PPC64CompilationCallback,24\n"
    218     ".previous\n"
    219     ".align 4\n"
    220     ".type PPC64CompilationCallback,@function\n"
    221 ".L.PPC64CompilationCallback:\n"
    222 #else
    223 asm(
    224     ".text\n"
    225     ".align 2\n"
    226     ".globl _PPC64CompilationCallback\n"
    227 "_PPC64CompilationCallback:\n"
    228 #endif
    229     // Make space for 8 ints r[3-10] and 13 doubles f[1-13] and the
    230     // FIXME: need to save v[0-19] for altivec?
    231     // Set up a proper stack frame
    232     // Layout
    233     //   PowerPC64 ABI linkage    -  48 bytes
    234     //                 parameters -  64 bytes
    235     //   13 double registers      - 104 bytes
    236     //   8 int registers          -  64 bytes
    237     "mflr 0\n"
    238     "std  0,  16(1)\n"
    239     "stdu 1, -280(1)\n"
    240     // Save all int arg registers
    241     "std 10, 272(1)\n"    "std 9,  264(1)\n"
    242     "std 8,  256(1)\n"    "std 7,  248(1)\n"
    243     "std 6,  240(1)\n"    "std 5,  232(1)\n"
    244     "std 4,  224(1)\n"    "std 3,  216(1)\n"
    245     // Save all call-clobbered FP regs.
    246     "stfd 13, 208(1)\n"    "stfd 12, 200(1)\n"
    247     "stfd 11, 192(1)\n"    "stfd 10, 184(1)\n"
    248     "stfd 9,  176(1)\n"    "stfd 8,  168(1)\n"
    249     "stfd 7,  160(1)\n"    "stfd 6,  152(1)\n"
    250     "stfd 5,  144(1)\n"    "stfd 4,  136(1)\n"
    251     "stfd 3,  128(1)\n"    "stfd 2,  120(1)\n"
    252     "stfd 1,  112(1)\n"
    253     // Arguments to Compilation Callback:
    254     // r3 - our lr (address of the call instruction in stub plus 4)
    255     // r4 - stub's lr (address of instruction that called the stub plus 4)
    256     // r5 - is64Bit - always 1.
    257     "mr   3, 0\n"      // return address (still in r0)
    258     "ld   5, 280(1)\n" // stub's frame
    259     "ld   4, 16(5)\n"  // stub's lr
    260     "li   5, 1\n"      // 1 == 64 bit
    261 #ifdef __ELF__
    262     "bl PPCCompilationCallbackC\n"
    263     "nop\n"
    264 #else
    265     "bl _PPCCompilationCallbackC\n"
    266 #endif
    267     "mtctr 3\n"
    268     // Restore all int arg registers
    269     "ld 10, 272(1)\n"    "ld 9,  264(1)\n"
    270     "ld 8,  256(1)\n"    "ld 7,  248(1)\n"
    271     "ld 6,  240(1)\n"    "ld 5,  232(1)\n"
    272     "ld 4,  224(1)\n"    "ld 3,  216(1)\n"
    273     // Restore all FP arg registers
    274     "lfd 13, 208(1)\n"    "lfd 12, 200(1)\n"
    275     "lfd 11, 192(1)\n"    "lfd 10, 184(1)\n"
    276     "lfd 9,  176(1)\n"    "lfd 8,  168(1)\n"
    277     "lfd 7,  160(1)\n"    "lfd 6,  152(1)\n"
    278     "lfd 5,  144(1)\n"    "lfd 4,  136(1)\n"
    279     "lfd 3,  128(1)\n"    "lfd 2,  120(1)\n"
    280     "lfd 1,  112(1)\n"
    281     // Pop 3 frames off the stack and branch to target
    282     "ld  1, 280(1)\n"
    283     "ld  0, 16(1)\n"
    284     "mtlr 0\n"
    285     // XXX: any special TOC handling in the ELF case for JIT?
    286     "bctr\n"
    287     );
    288 #else
    289 void PPC64CompilationCallback() {
    290   llvm_unreachable("This is not a power pc, you can't execute this!");
    291 }
    292 #endif
    293 
    294 extern "C" void *PPCCompilationCallbackC(unsigned *StubCallAddrPlus4,
    295                                          unsigned *OrigCallAddrPlus4,
    296                                          bool is64Bit) {
    297   // Adjust the pointer to the address of the call instruction in the stub
    298   // emitted by emitFunctionStub, rather than the instruction after it.
    299   unsigned *StubCallAddr = StubCallAddrPlus4 - 1;
    300   unsigned *OrigCallAddr = OrigCallAddrPlus4 - 1;
    301 
    302   void *Target = JITCompilerFunction(StubCallAddr);
    303 
    304   // Check to see if *OrigCallAddr is a 'bl' instruction, and if we can rewrite
    305   // it to branch directly to the destination.  If so, rewrite it so it does not
    306   // need to go through the stub anymore.
    307   unsigned OrigCallInst = *OrigCallAddr;
    308   if ((OrigCallInst >> 26) == 18) {     // Direct call.
    309     intptr_t Offset = ((intptr_t)Target - (intptr_t)OrigCallAddr) >> 2;
    310 
    311     if (Offset >= -(1 << 23) && Offset < (1 << 23)) {   // In range?
    312       // Clear the original target out.
    313       OrigCallInst &= (63 << 26) | 3;
    314       // Fill in the new target.
    315       OrigCallInst |= (Offset & ((1 << 24)-1)) << 2;
    316       // Replace the call.
    317       *OrigCallAddr = OrigCallInst;
    318     }
    319   }
    320 
    321   // Assert that we are coming from a stub that was created with our
    322   // emitFunctionStub.
    323   if ((*StubCallAddr >> 26) == 18)
    324     StubCallAddr -= 3;
    325   else {
    326   assert((*StubCallAddr >> 26) == 19 && "Call in stub is not indirect!");
    327     StubCallAddr -= is64Bit ? 9 : 6;
    328   }
    329 
    330   // Rewrite the stub with an unconditional branch to the target, for any users
    331   // who took the address of the stub.
    332   EmitBranchToAt((intptr_t)StubCallAddr, (intptr_t)Target, false, is64Bit);
    333   sys::Memory::InvalidateInstructionCache(StubCallAddr, 7*4);
    334 
    335   // Put the address of the target function to call and the address to return to
    336   // after calling the target function in a place that is easy to get on the
    337   // stack after we restore all regs.
    338   return Target;
    339 }
    340 
    341 
    342 
    343 TargetJITInfo::LazyResolverFn
    344 PPCJITInfo::getLazyResolverFunction(JITCompilerFn Fn) {
    345   JITCompilerFunction = Fn;
    346   return is64Bit ? PPC64CompilationCallback : PPC32CompilationCallback;
    347 }
    348 
    349 TargetJITInfo::StubLayout PPCJITInfo::getStubLayout() {
    350   // The stub contains up to 10 4-byte instructions, aligned at 4 bytes: 3
    351   // instructions to save the caller's address if this is a lazy-compilation
    352   // stub, plus a 1-, 4-, or 7-instruction sequence to load an arbitrary address
    353   // into a register and jump through it.
    354   StubLayout Result = {10*4, 4};
    355   return Result;
    356 }
    357 
    358 #if (defined(__POWERPC__) || defined (__ppc__) || defined(_POWER)) && \
    359 defined(__APPLE__)
    360 extern "C" void sys_icache_invalidate(const void *Addr, size_t len);
    361 #endif
    362 
    363 void *PPCJITInfo::emitFunctionStub(const Function* F, void *Fn,
    364                                    JITCodeEmitter &JCE) {
    365   // If this is just a call to an external function, emit a branch instead of a
    366   // call.  The code is the same except for one bit of the last instruction.
    367   if (Fn != (void*)(intptr_t)PPC32CompilationCallback &&
    368       Fn != (void*)(intptr_t)PPC64CompilationCallback) {
    369     void *Addr = (void*)JCE.getCurrentPCValue();
    370     JCE.emitWordBE(0);
    371     JCE.emitWordBE(0);
    372     JCE.emitWordBE(0);
    373     JCE.emitWordBE(0);
    374     JCE.emitWordBE(0);
    375     JCE.emitWordBE(0);
    376     JCE.emitWordBE(0);
    377     EmitBranchToAt((intptr_t)Addr, (intptr_t)Fn, false, is64Bit);
    378     sys::Memory::InvalidateInstructionCache(Addr, 7*4);
    379     return Addr;
    380   }
    381 
    382   void *Addr = (void*)JCE.getCurrentPCValue();
    383   if (is64Bit) {
    384     JCE.emitWordBE(0xf821ffb1);     // stdu r1,-80(r1)
    385     JCE.emitWordBE(0x7d6802a6);     // mflr r11
    386     JCE.emitWordBE(0xf9610060);     // std r11, 96(r1)
    387   } else if (TM.getSubtargetImpl()->isDarwinABI()){
    388     JCE.emitWordBE(0x9421ffe0);     // stwu r1,-32(r1)
    389     JCE.emitWordBE(0x7d6802a6);     // mflr r11
    390     JCE.emitWordBE(0x91610028);     // stw r11, 40(r1)
    391   } else {
    392     JCE.emitWordBE(0x9421ffe0);     // stwu r1,-32(r1)
    393     JCE.emitWordBE(0x7d6802a6);     // mflr r11
    394     JCE.emitWordBE(0x91610024);     // stw r11, 36(r1)
    395   }
    396   intptr_t BranchAddr = (intptr_t)JCE.getCurrentPCValue();
    397   JCE.emitWordBE(0);
    398   JCE.emitWordBE(0);
    399   JCE.emitWordBE(0);
    400   JCE.emitWordBE(0);
    401   JCE.emitWordBE(0);
    402   JCE.emitWordBE(0);
    403   JCE.emitWordBE(0);
    404   EmitBranchToAt(BranchAddr, (intptr_t)Fn, true, is64Bit);
    405   sys::Memory::InvalidateInstructionCache(Addr, 10*4);
    406   return Addr;
    407 }
    408 
    409 
    410 void PPCJITInfo::relocate(void *Function, MachineRelocation *MR,
    411                           unsigned NumRelocs, unsigned char* GOTBase) {
    412   for (unsigned i = 0; i != NumRelocs; ++i, ++MR) {
    413     unsigned *RelocPos = (unsigned*)Function + MR->getMachineCodeOffset()/4;
    414     intptr_t ResultPtr = (intptr_t)MR->getResultPointer();
    415     switch ((PPC::RelocationType)MR->getRelocationType()) {
    416     default: llvm_unreachable("Unknown relocation type!");
    417     case PPC::reloc_pcrel_bx:
    418       // PC-relative relocation for b and bl instructions.
    419       ResultPtr = (ResultPtr-(intptr_t)RelocPos) >> 2;
    420       assert(ResultPtr >= -(1 << 23) && ResultPtr < (1 << 23) &&
    421              "Relocation out of range!");
    422       *RelocPos |= (ResultPtr & ((1 << 24)-1))  << 2;
    423       break;
    424     case PPC::reloc_pcrel_bcx:
    425       // PC-relative relocation for BLT,BLE,BEQ,BGE,BGT,BNE, or other
    426       // bcx instructions.
    427       ResultPtr = (ResultPtr-(intptr_t)RelocPos) >> 2;
    428       assert(ResultPtr >= -(1 << 13) && ResultPtr < (1 << 13) &&
    429              "Relocation out of range!");
    430       *RelocPos |= (ResultPtr & ((1 << 14)-1))  << 2;
    431       break;
    432     case PPC::reloc_absolute_high:     // high bits of ref -> low 16 of instr
    433     case PPC::reloc_absolute_low: {    // low bits of ref  -> low 16 of instr
    434       ResultPtr += MR->getConstantVal();
    435 
    436       // If this is a high-part access, get the high-part.
    437       if (MR->getRelocationType() == PPC::reloc_absolute_high) {
    438         // If the low part will have a carry (really a borrow) from the low
    439         // 16-bits into the high 16, add a bit to borrow from.
    440         if (((int)ResultPtr << 16) < 0)
    441           ResultPtr += 1 << 16;
    442         ResultPtr >>= 16;
    443       }
    444 
    445       // Do the addition then mask, so the addition does not overflow the 16-bit
    446       // immediate section of the instruction.
    447       unsigned LowBits  = (*RelocPos + ResultPtr) & 65535;
    448       unsigned HighBits = *RelocPos & ~65535;
    449       *RelocPos = LowBits | HighBits;  // Slam into low 16-bits
    450       break;
    451     }
    452     case PPC::reloc_absolute_low_ix: {  // low bits of ref  -> low 14 of instr
    453       ResultPtr += MR->getConstantVal();
    454       // Do the addition then mask, so the addition does not overflow the 16-bit
    455       // immediate section of the instruction.
    456       unsigned LowBits  = (*RelocPos + ResultPtr) & 0xFFFC;
    457       unsigned HighBits = *RelocPos & 0xFFFF0003;
    458       *RelocPos = LowBits | HighBits;  // Slam into low 14-bits.
    459       break;
    460     }
    461     }
    462   }
    463 }
    464 
    465 void PPCJITInfo::replaceMachineCodeForFunction(void *Old, void *New) {
    466   EmitBranchToAt((intptr_t)Old, (intptr_t)New, false, is64Bit);
    467   sys::Memory::InvalidateInstructionCache(Old, 7*4);
    468 }
    469