Use movw/movt instead of constant pool on ARMv7

src/arm/assembler-arm.cc

 // Copyright (c) 1994-2006 Sun Microsystems Inc.
 // All Rights Reserved.
 //
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions
 // are met:
 //
 // - Redistributions of source code must retain the above copyright notice,
 // this list of conditions and the following disclaimer.
 //
@@ skipping 99 matching lines @@
     supported_ |= 1u << VFP3 | 1u << ARMv7 | 1u << VFP2;
   }
   // For the simulator=arm build, use ARMv7 when FLAG_enable_armv7 is enabled
   if (FLAG_enable_armv7) {
     supported_ |= 1u << ARMv7;
   }
 
   if (FLAG_enable_sudiv) {
     supported_ |= 1u << SUDIV;
   }
+
+  if (FLAG_enable_movw_movt) {
+    supported_ |= 1u << MOVW_MOVT_IMMEDIATE_LOADS;
+  }
 #else  // __arm__
   // Probe for additional features not already known to be available.
   if (!IsSupported(VFP3) && OS::ArmCpuHasFeature(VFP3)) {
     // This implementation also sets the VFP flags if runtime
     // detection of VFP returns true. VFPv3 implies ARMv7 and VFP2, see ARM DDI
     // 0406B, page A1-6.
     found_by_runtime_probing_ |= 1u << VFP3 | 1u << ARMv7 | 1u << VFP2;
   } else if (!IsSupported(VFP2) && OS::ArmCpuHasFeature(VFP2)) {
     found_by_runtime_probing_ |= 1u << VFP2;
   }
 
   if (!IsSupported(ARMv7) && OS::ArmCpuHasFeature(ARMv7)) {
     found_by_runtime_probing_ |= 1u << ARMv7;
   }
 
   if (!IsSupported(SUDIV) && OS::ArmCpuHasFeature(SUDIV)) {
     found_by_runtime_probing_ |= 1u << SUDIV;
   }
 
   if (!IsSupported(UNALIGNED_ACCESSES) && OS::ArmCpuHasFeature(ARMv7)) {
     found_by_runtime_probing_ |= 1u << UNALIGNED_ACCESSES;
   }
 
+  if (OS::GetCpuImplementer() == QualcommImplementer &&
+      OS::ArmCpuHasFeature(ARMv7)) {
+    found_by_runtime_probing_ |= 1u << MOVW_MOVT_IMMEDIATE_LOADS;
+  }
+
   supported_ |= found_by_runtime_probing_;
 #endif
 
   // Assert that VFP3 implies VFP2 and ARMv7.
   ASSERT(!IsSupported(VFP3) || (IsSupported(VFP2) && IsSupported(ARMv7)));
 }
 
 
 // -----------------------------------------------------------------------------
 // Implementation of RelocInfo
@@ skipping 570 matching lines @@
   int link = target_at(L->pos());
   if (link == kEndOfChain) {
     L->Unuse();
   } else {
     ASSERT(link >= 0);
     L->link_to(link);
   }
 }
 
 
-static Instr EncodeMovwImmediate(uint32_t immediate) {
-  ASSERT(immediate < 0x10000);
-  return ((immediate & 0xf000) << 4) | (immediate & 0xfff);
-}
-
-
 // Low-level code emission routines depending on the addressing mode.
 // If this returns true then you have to use the rotate_imm and immed_8
 // that it returns, because it may have already changed the instruction
 // to match them!
 static bool fits_shifter(uint32_t imm32,
                          uint32_t* rotate_imm,
                          uint32_t* immed_8,
                          Instr* instr) {
   // imm32 must be unsigned.
   for (int rot = 0; rot < 16; rot++) {
@@ skipping 44 matching lines @@
     }
   }
   return false;
 }
 
 
 // We have to use the temporary register for things that can be relocated even
 // if they can be encoded in the ARM's 12 bits of immediate-offset instruction
 // space.  There is no guarantee that the relocated location can be similarly
 // encoded.
-bool Operand::must_use_constant_pool(const Assembler* assembler) const {
+bool Operand::must_output_reloc_info(const Assembler* assembler) const {
   if (rmode_ == RelocInfo::EXTERNAL_REFERENCE) {
 #ifdef DEBUG
     if (!Serializer::enabled()) {
       Serializer::TooLateToEnableNow();
     }
 #endif  // def DEBUG
     if (assembler != NULL && assembler->predictable_code_size()) return true;
     return Serializer::enabled();
   } else if (rmode_ == RelocInfo::NONE) {
     return false;
   }
   return true;
 }
 
 
 bool Operand::is_single_instruction(const Assembler* assembler,
                                     Instr instr) const {
   if (rm_.is_valid()) return true;
   uint32_t dummy1, dummy2;
-  if (must_use_constant_pool(assembler) ||
+  if (must_output_reloc_info(assembler) ||
       !fits_shifter(imm32_, &dummy1, &dummy2, &instr)) {
     // The immediate operand cannot be encoded as a shifter operand, or use of
     // constant pool is required. For a mov instruction not setting the
     // condition code additional instruction conventions can be used.
     if ((instr & ~kCondMask) == 13*B21) {  // mov, S not set
-      if (must_use_constant_pool(assembler) ||
-          !CpuFeatures::IsSupported(ARMv7)) {
-        // mov instruction will be an ldr from constant pool (one instruction).
-        return true;
-      } else {
-        // mov instruction will be a mov or movw followed by movt (two
-        // instructions).
-        return false;
-      }
+#ifdef USE_BLX
+      // When using BLX, there are two things that must be true for the address
+      // load to be longer than a single instruction. First, immediate loads
+      // using movw/movt must be supported (and fast) on the target ARM
+      // architecture. Second, the reloc mode must be something other than NONE,
+      // since NONE is a used whenever the constant pool cannot be used for
+      // technical reasons, e.g. back-patching calls site in optimized code with
+      // a call to a lazy deopt routine.
+      return !Assembler::allow_immediate_constant_pool_loads(assembler) &&
+          rmode_ != RelocInfo::NONE;
+#else
+      return true;

[ulan, 2012/10/18 09:07:53]

Why don't we check for !CpuFeatures::IsSupported(ARMv7) in this case?

[danno, 2012/10/18 12:22:10]

It's not possible to use immediate loads to the pc to do a call, so loading the
destination address without USE_BLX is always a single instruction of the form
ldr pc, [pc + #xxx].On 2012/10/18 09:07:53, ulan wrote:

+#endif
     } else {
       // If this is not a mov or mvn instruction there will always an additional
       // instructions - either mov or ldr. The mov might actually be two
       // instructions mov or movw followed by movt so including the actual
       // instruction two or three instructions will be generated.
       return false;
     }
   } else {
     // No use of constant pool and the immediate operand can be encoded as a
     // shifter operand.
     return true;
   }
 }
 
 
+void Assembler::move_32_bit_immediate(Condition cond,
+                                      Register rd,
+                                      SBit s,
+                                      const Operand& x) {
+  if (rd.code() != pc.code() && s == LeaveCC) {
+    // Candidate for immediate load.
+    if (x.must_output_reloc_info(this)) {
+      if (!Assembler::allow_immediate_constant_pool_loads(this)) {
+        RecordRelocInfo(x.rmode_, x.imm32_, USE_CONSTANT_POOL);
+        ldr(rd, MemOperand(pc, 0), cond);
+        return;
+      }
+      RecordRelocInfo(x.rmode_, x.imm32_, DONT_USE_CONSTANT_POOL);
+      // Make sure the movw/movt doesn't get separated.
+      BlockConstPoolFor(2);
+    }
+
+    // Emit a real movw/movt pair.
+    emit(cond | 0x30*B20 | rd.code()*B12 |
+         EncodeMovwImmediate(x.imm32_ & 0xffff));
+    movt(rd, static_cast<uint32_t>(x.imm32_) >> 16, cond);
+  } else {
+    RecordRelocInfo(x.rmode_, x.imm32_, USE_CONSTANT_POOL);
+    ldr(rd, MemOperand(pc, 0), cond);
+  }
+}
+
+
 void Assembler::addrmod1(Instr instr,
                          Register rn,
                          Register rd,
                          const Operand& x) {
   CheckBuffer();
   ASSERT((instr & ~(kCondMask | kOpCodeMask | S)) == 0);
   if (!x.rm_.is_valid()) {
     // Immediate.
     uint32_t rotate_imm;
     uint32_t immed_8;
-    if (x.must_use_constant_pool(this) ||
+    if (x.must_output_reloc_info(this) ||
         !fits_shifter(x.imm32_, &rotate_imm, &immed_8, &instr)) {
       // The immediate operand cannot be encoded as a shifter operand, so load
       // it first to register ip and change the original instruction to use ip.
       // However, if the original instruction is a 'mov rd, x' (not setting the
       // condition code), then replace it with a 'ldr rd, [pc]'.
       CHECK(!rn.is(ip));  // rn should never be ip, or will be trashed
       Condition cond = Instruction::ConditionField(instr);
       if ((instr & ~kCondMask) == 13*B21) {  // mov, S not set
-        if (x.must_use_constant_pool(this) ||
-            !CpuFeatures::IsSupported(ARMv7)) {
-          RecordRelocInfo(x.rmode_, x.imm32_);
-          ldr(rd, MemOperand(pc, 0), cond);
-        } else {
-          // Will probably use movw, will certainly not use constant pool.
-          mov(rd, Operand(x.imm32_ & 0xffff), LeaveCC, cond);
-          movt(rd, static_cast<uint32_t>(x.imm32_) >> 16, cond);
-        }
+        move_32_bit_immediate(cond, rd, LeaveCC, x);
       } else {
         // If this is not a mov or mvn instruction we may still be able to avoid
         // a constant pool entry by using mvn or movw.
-        if (!x.must_use_constant_pool(this) &&
+        if (!x.must_output_reloc_info(this) &&
             (instr & kMovMvnMask) != kMovMvnPattern) {
           mov(ip, x, LeaveCC, cond);
         } else {
-          RecordRelocInfo(x.rmode_, x.imm32_);
-          ldr(ip, MemOperand(pc, 0), cond);
+          move_32_bit_immediate(cond, ip,
+                                static_cast<SBit>(instr & (1 << 20)), x);
         }
         addrmod1(instr, rn, rd, Operand(ip));
       }
       return;
     }
     instr |= I | rotate_imm*B8 | immed_8;
   } else if (!x.rs_.is_valid()) {
     // Immediate shift.
     instr |= x.shift_imm_*B7 | x.shift_op_ | x.rm_.code();
   } else {
@@ skipping 286 matching lines @@
   // Don't allow nop instructions in the form mov rn, rn to be generated using
   // the mov instruction. They must be generated using nop(int/NopMarkerTypes)
   // or MarkCode(int/NopMarkerTypes) pseudo instructions.
   ASSERT(!(src.is_reg() && src.rm().is(dst) && s == LeaveCC && cond == al));
   addrmod1(cond | MOV | s, r0, dst, src);
 }
 
 
 void Assembler::movw(Register reg, uint32_t immediate, Condition cond) {
   ASSERT(immediate < 0x10000);
+  // May use movw if supported, but on unsupported platforms will try to use
+  // equivalent rotated immed_8 value and other tricks before falling back to a
+  // constant pool load.
   mov(reg, Operand(immediate), LeaveCC, cond);
 }
 
 
 void Assembler::movt(Register reg, uint32_t immediate, Condition cond) {
   emit(cond | 0x34*B20 | reg.code()*B12 | EncodeMovwImmediate(immediate));
 }
 
 
 void Assembler::bic(Register dst, Register src1, const Operand& src2,
@@ skipping 209 matching lines @@
 
 
 void Assembler::msr(SRegisterFieldMask fields, const Operand& src,
                     Condition cond) {
   ASSERT(fields >= B16 && fields < B20);  // at least one field set
   Instr instr;
   if (!src.rm_.is_valid()) {
     // Immediate.
     uint32_t rotate_imm;
     uint32_t immed_8;
-    if (src.must_use_constant_pool(this) ||
+    if (src.must_output_reloc_info(this) ||
         !fits_shifter(src.imm32_, &rotate_imm, &immed_8, NULL)) {
       // Immediate operand cannot be encoded, load it first to register ip.
       RecordRelocInfo(src.rmode_, src.imm32_);
       ldr(ip, MemOperand(pc, 0), cond);
       msr(fields, Operand(ip), cond);
       return;
     }
     instr = I | rotate_imm*B8 | immed_8;
   } else {
     ASSERT(!src.rs_.is_valid() && src.shift_imm_ == 0);  // only rm allowed
@@ skipping 1007 matching lines @@
   // ARMv6{K/T2} and v7 have an actual NOP instruction but it serializes
   // some of the CPU's pipeline and has to issue. Older ARM chips simply used
   // MOV Rx, Rx as NOP and it performs better even in newer CPUs.
   // We therefore use MOV Rx, Rx, even on newer CPUs, and use Rx to encode
   // a type.
   ASSERT(0 <= type && type <= 14);  // mov pc, pc isn't a nop.
   emit(al | 13*B21 | type*B12 | type);
 }
 
 
+bool Assembler::IsMovT(Instr instr) {
+  instr &= ~(((kNumberOfConditions - 1) << 28) |  // Mask off conditions
+             ((kNumRegisters-1)*B12) |            // mask out register
+             EncodeMovwImmediate(0xFFFF));        // mask out immediate value
+  return instr == 0x34*B20;
+}
+
+
+bool Assembler::IsMovW(Instr instr) {
+  instr &= ~(((kNumberOfConditions - 1) << 28) |  // Mask off conditions
+             ((kNumRegisters-1)*B12) |            // mask out destination
+             EncodeMovwImmediate(0xFFFF));        // mask out immediate value
+  return instr == 0x30*B20;
+}
+
+
 bool Assembler::IsNop(Instr instr, int type) {
   ASSERT(0 <= type && type <= 14);  // mov pc, pc isn't a nop.
   // Check for mov rx, rx where x = type.
   return instr == (al | 13*B21 | type*B12 | type);
 }
 
 
 bool Assembler::ImmediateFitsAddrMode1Instruction(int32_t imm32) {
   uint32_t dummy1;
   uint32_t dummy2;
@@ skipping 98 matching lines @@
   // No relocation info should be pending while using dd. dd is used
   // to write pure data with no pointers and the constant pool should
   // be emitted before using dd.
   ASSERT(num_pending_reloc_info_ == 0);
   CheckBuffer();
   *reinterpret_cast<uint32_t*>(pc_) = data;
   pc_ += sizeof(uint32_t);
 }
 
 
-void Assembler::RecordRelocInfo(RelocInfo::Mode rmode, intptr_t data) {
+void Assembler::RecordRelocInfo(RelocInfo::Mode rmode, intptr_t data,
+                                UseConstantPoolMode mode) {
   // We do not try to reuse pool constants.
   RelocInfo rinfo(pc_, rmode, data, NULL);
   if (((rmode >= RelocInfo::JS_RETURN) &&
        (rmode <= RelocInfo::DEBUG_BREAK_SLOT)) ||
-      (rmode == RelocInfo::CONST_POOL)) {
+      (rmode == RelocInfo::CONST_POOL) ||
+      mode == DONT_USE_CONSTANT_POOL) {
     // Adjust code for new modes.
     ASSERT(RelocInfo::IsDebugBreakSlot(rmode)
            || RelocInfo::IsJSReturn(rmode)
            || RelocInfo::IsComment(rmode)
            || RelocInfo::IsPosition(rmode)
-           || RelocInfo::IsConstPool(rmode));
+           || RelocInfo::IsConstPool(rmode)
+           || mode == DONT_USE_CONSTANT_POOL);
     // These modes do not need an entry in the constant pool.
   } else {
     ASSERT(num_pending_reloc_info_ < kMaxNumPendingRelocInfo);
     if (num_pending_reloc_info_ == 0) {
       first_const_pool_use_ = pc_offset();
     }
     pending_reloc_info_[num_pending_reloc_info_++] = rinfo;
     // Make sure the constant pool is not emitted in place of the next
     // instruction for which we just recorded relocation info.
     BlockConstPoolFor(1);
@@ skipping 98 matching lines @@
     // Emit constant pool entries.
     for (int i = 0; i < num_pending_reloc_info_; i++) {
       RelocInfo& rinfo = pending_reloc_info_[i];
       ASSERT(rinfo.rmode() != RelocInfo::COMMENT &&
              rinfo.rmode() != RelocInfo::POSITION &&
              rinfo.rmode() != RelocInfo::STATEMENT_POSITION &&
              rinfo.rmode() != RelocInfo::CONST_POOL);
 
       Instr instr = instr_at(rinfo.pc());
       // Instruction to patch must be 'ldr rd, [pc, #offset]' with offset == 0.
-      ASSERT(IsLdrPcImmediateOffset(instr) &&
-             GetLdrRegisterImmediateOffset(instr) == 0);
+      if (IsLdrPcImmediateOffset(instr) &&
+          GetLdrRegisterImmediateOffset(instr) == 0) {
+        int delta = pc_ - rinfo.pc() - kPcLoadDelta;
+        // 0 is the smallest delta:
+        //   ldr rd, [pc, #0]
+        //   constant pool marker
+        //   data
+        ASSERT(is_uint12(delta));
 
-      int delta = pc_ - rinfo.pc() - kPcLoadDelta;
-      // 0 is the smallest delta:
-      //   ldr rd, [pc, #0]
-      //   constant pool marker
-      //   data
-      ASSERT(is_uint12(delta));
-
-      instr_at_put(rinfo.pc(), SetLdrRegisterImmediateOffset(instr, delta));
+        instr_at_put(rinfo.pc(), SetLdrRegisterImmediateOffset(instr, delta));
+      } else {
+        ASSERT(IsMovW(instr));
+      }
       emit(rinfo.data());
     }
 
     num_pending_reloc_info_ = 0;
     first_const_pool_use_ = -1;
 
     RecordComment("]");
 
     if (after_pool.is_linked()) {
       bind(&after_pool);
     }
   }
 
   // Since a constant pool was just emitted, move the check offset forward by
   // the standard interval.
   next_buffer_check_ = pc_offset() + kCheckPoolInterval;
 }
 
 
 } }  // namespace v8::internal
 
 #endif  // V8_TARGET_ARCH_ARM