[MIPS] Modify LongBranch expansion to work with sandboxing

lib/Target/Mips/MipsLongBranch.cpp

Index: lib/Target/Mips/MipsLongBranch.cpp
diff --git a/lib/Target/Mips/MipsLongBranch.cpp b/lib/Target/Mips/MipsLongBranch.cpp
index 24b42b9150447a9da5925368352fe8c3e9e0dbdb..e8fe1214bb0273a9272aa5a9eeeff39b141e24d0 100644
--- a/lib/Target/Mips/MipsLongBranch.cpp
+++ b/lib/Target/Mips/MipsLongBranch.cpp
@@ -68,7 +68,8 @@ namespace {
         TII(static_cast<const MipsInstrInfo*>(tm.getInstrInfo())),
         IsPIC(TM.getRelocationModel() == Reloc::PIC_),
         ABI(TM.getSubtarget<MipsSubtarget>().getTargetABI()),
-        LongBranchSeqSize(!IsPIC ? 2 : (ABI == MipsSubtarget::N64 ? 13 : 9)) {}
+        LongBranchSeqSize(!IsPIC ? 2 : (ABI == MipsSubtarget::N64 ? 13 :
+            (/*@LOCALMOD*/Triple(TM.getTargetTriple()).isOSNaCl() ? 10 : 9))) {}
 
     virtual const char *getPassName() const {
       return "Mips Long Branch";
@@ -263,7 +264,9 @@ void MipsLongBranch::expandToLongBranch(MBBInfo &I) {
     BalTgtMBB->addSuccessor(TgtMBB);
 
     int64_t TgtAddress = MBBInfos[TgtMBB->getNumber()].Address;
-    unsigned BalTgtMBBSize = 5;
+    // @LOCALMOD-START
+    unsigned BalTgtMBBSize = Triple(TM.getTargetTriple()).isOSNaCl() ? 6 : 5;
+    // @LOCALMOD-END
     int64_t Offset = TgtAddress - (I.Address + I.Size - BalTgtMBBSize * 4);
     int64_t Lo = SignExtend64<16>(Offset & 0xffff);
     int64_t Hi = SignExtend64<16>(((Offset + 0x8000) >> 16) & 0xffff);
@@ -290,23 +293,69 @@ void MipsLongBranch::expandToLongBranch(MBBInfo &I) {
       BuildMI(*LongBrMBB, Pos, DL, TII->get(Mips::SW)).addReg(Mips::RA)
         .addReg(Mips::SP).addImm(0);
 
-      MIBundleBuilder(*LongBrMBB, Pos)
-        .append(BuildMI(*MF, DL, TII->get(Mips::BAL_BR)).addMBB(BalTgtMBB))
-        .append(BuildMI(*MF, DL, TII->get(Mips::LUi), Mips::AT).addImm(Hi));
-
-      Pos = BalTgtMBB->begin();
-
-      BuildMI(*BalTgtMBB, Pos, DL, TII->get(Mips::ADDiu), Mips::AT)
-        .addReg(Mips::AT).addImm(Lo);
-      BuildMI(*BalTgtMBB, Pos, DL, TII->get(Mips::ADDu), Mips::AT)
-        .addReg(Mips::RA).addReg(Mips::AT);
-      BuildMI(*BalTgtMBB, Pos, DL, TII->get(Mips::LW), Mips::RA)
-        .addReg(Mips::SP).addImm(0);
-
-      MIBundleBuilder(*BalTgtMBB, Pos)
-        .append(BuildMI(*MF, DL, TII->get(Mips::JR)).addReg(Mips::AT))
-        .append(BuildMI(*MF, DL, TII->get(Mips::ADDiu), Mips::SP)
-                .addReg(Mips::SP).addImm(8));
+      if (Triple(TM.getTargetTriple()).isOSNaCl()) {
+        // @LOCALMOD-START
+        // LUi and ADDiu instructions create 32-bit offset of the target basic
+        // block from the BAL target. We cannot use immediate value as the
+        // offset (as non-NaCl version does) because it does not take
+        // sandboxed instructions into account ("sanboxing" is run after this
+        // pass). We therefore replace it with relocation expressions
+        // %hi($tgt-$baltgt) and %lo($tgt-$baltgt). This expressions are
+        // resolved during the fixup after all sandboxing code is added, so the
+        // values will always be correct.
+        //
+        // Since we cannot create %hi($tgt-$baltgt) and %lo($tgt-$baltgt)
+        // expressions at this point (it is possible only at the MC layer),
+        // we replace LUi and ADDiu with pseudo instructions
+        // NACL_LONG_BRANCH_LUi and NACL_LONG_BRANCH_ADDiu, and add both basic
+        // block as operands to these instructions. When lowering these pseudo
+        // instructions to LUi and ADDiu in the MC layer, we will create
+        // %hi($tgt-$baltgt) and %lo($tgt-$baltgt) expressions add add them as
+        // operands to lowered instructions.
+        MIBundleBuilder(*LongBrMBB, Pos)
+          .append(BuildMI(*MF, DL, TII->get(Mips::BAL_BR)).addMBB(BalTgtMBB))
+          .append(BuildMI(*MF, DL, TII->get(Mips::NACL_LONG_BRANCH_LUi),
+                          Mips::AT).addMBB(TgtMBB).addMBB(BalTgtMBB));
+
+        Pos = BalTgtMBB->begin();
+
+        BuildMI(*BalTgtMBB, Pos, DL, TII->get(Mips::NACL_LONG_BRANCH_ADDiu),
+                Mips::AT).addReg(Mips::AT).addMBB(TgtMBB).addMBB(BalTgtMBB);
+        BuildMI(*BalTgtMBB, Pos, DL, TII->get(Mips::ADDu), Mips::AT)
+          .addReg(Mips::RA).addReg(Mips::AT);
+        BuildMI(*BalTgtMBB, Pos, DL, TII->get(Mips::LW), Mips::RA)
+          .addReg(Mips::SP).addImm(0);
+
+        // In NaCl, modifying sp is not allowed in branch delay slot.
+        BuildMI(*BalTgtMBB, Pos, DL, TII->get(Mips::ADDiu), Mips::SP)
+          .addReg(Mips::SP).addImm(8);
+
+        MIBundleBuilder(*BalTgtMBB, Pos)
+          .append(BuildMI(*MF, DL, TII->get(Mips::JR)).addReg(Mips::AT))
+          .append(BuildMI(*MF, DL, TII->get(Mips::NOP)));
+
+        // Align target of JR instruction.
+        TgtMBB->setAlignment(4);
+        // @LOCALMOD-END
+      } else {
+        MIBundleBuilder(*LongBrMBB, Pos)
+          .append(BuildMI(*MF, DL, TII->get(Mips::BAL_BR)).addMBB(BalTgtMBB))
+          .append(BuildMI(*MF, DL, TII->get(Mips::LUi), Mips::AT).addImm(Hi));
+
+        Pos = BalTgtMBB->begin();
+
+        BuildMI(*BalTgtMBB, Pos, DL, TII->get(Mips::ADDiu), Mips::AT)
+          .addReg(Mips::AT).addImm(Lo);
+        BuildMI(*BalTgtMBB, Pos, DL, TII->get(Mips::ADDu), Mips::AT)
+          .addReg(Mips::RA).addReg(Mips::AT);
+        BuildMI(*BalTgtMBB, Pos, DL, TII->get(Mips::LW), Mips::RA)
+          .addReg(Mips::SP).addImm(0);
+
+        MIBundleBuilder(*BalTgtMBB, Pos)
+          .append(BuildMI(*MF, DL, TII->get(Mips::JR)).addReg(Mips::AT))
+          .append(BuildMI(*MF, DL, TII->get(Mips::ADDiu), Mips::SP)
+                  .addReg(Mips::SP).addImm(8));
+      }
     } else {
       // $longbr:
       //  daddiu $sp, $sp, -16
@@ -430,8 +479,23 @@ bool MipsLongBranch::runOnMachineFunction(MachineFunction &F) {
         continue;
 
       // Check if offset fits into 16-bit immediate field of branches.
-      if (!ForceLongBranch && isInt<16>(computeOffset(I->Br) / 4))
-        continue;
+      if (Triple(TM.getTargetTriple()).isOSNaCl()) {
+        // @LOCALMOD-START
+        int64_t Offset = computeOffset(I->Br) / 4;
+
+        // This offset calculation does not include sandboxing instructions
+        // that will be added later in the MC layer. Since at this point we
+        // don't know the exact amount of code that "sanboxing" will add, we
+        // conservatively estimate that code will not grow more than 100%.
+        Offset *= 2;
+
+        if (!ForceLongBranch && isInt<16>(Offset))
+          continue;
+        // @LOCALMOD-END
+      } else {
+        if (!ForceLongBranch && isInt<16>(computeOffset(I->Br) / 4))
+          continue;
+      }
 
       I->HasLongBranch = true;
       I->Size += LongBranchSeqSize * 4;