Load immediates via the constant pool on armv5te and armv6.

runtime/vm/assembler_arm.cc

 // Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #include "vm/globals.h"  // NOLINT
 #if defined(TARGET_ARCH_ARM)
 
 #include "vm/assembler.h"
 #include "vm/cpu.h"
 #include "vm/longjump.h"
@@ skipping 1507 matching lines @@
 
 
 void Assembler::Drop(intptr_t stack_elements) {
   ASSERT(stack_elements >= 0);
   if (stack_elements > 0) {
     AddImmediate(SP, SP, stack_elements * kWordSize);
   }
 }
 
 
+intptr_t Assembler::FindImmediate(int32_t imm) {
+  ASSERT(Isolate::Current() != Dart::vm_isolate());
+  const Smi& smi = Smi::Handle(reinterpret_cast<RawSmi*>(imm));
+  return object_pool_wrapper_.FindObject(smi);

[zra, 2015/07/23 22:45:59]

Why not use ObjectPoolWrapper::FindImmediate() ? I think that's what arm64 uses.

[regis, 2015/07/23 23:07:31]

Because I forked the code in May, when arm64 was still doing it this way :-)

Good point, thanks.

+}
+
+
 // Uses a code sequence that can easily be decoded.
 void Assembler::LoadWordFromPoolOffset(Register rd,
                                        int32_t offset,
                                        Condition cond) {
   ASSERT(constant_pool_allowed());
   ASSERT(rd != PP);
   int32_t offset_mask = 0;
   if (Address::CanHoldLoadOffset(kWord, offset, &offset_mask)) {
     ldr(rd, Address(PP, offset), cond);
   } else {
@@ skipping 10 matching lines @@
     ldr(rd, Address(rd, offset_lo), cond);
   }
 }
 
 
 void Assembler::LoadPoolPointer() {
   const intptr_t object_pool_pc_dist =
      Instructions::HeaderSize() - Instructions::object_pool_offset() +
      CodeSize() + Instr::kPCReadOffset;
   LoadFromOffset(kWord, PP, PC, -object_pool_pc_dist);
+  set_constant_pool_allowed(true);
 }
 
 
 void Assembler::LoadIsolate(Register rd) {
   ldr(rd, Address(THR, Thread::isolate_offset()));
 }
 
 
 void Assembler::LoadObjectHelper(Register rd,
                                  const Object& object,
@@ skipping 1171 matching lines @@
     movw(rd, value_low, cond);
     movt(rd, value_high, cond);
   }
 }
 
 
 void Assembler::LoadDecodableImmediate(
     Register rd, int32_t value, Condition cond) {
   const ARMVersion version = TargetCPUFeatures::arm_version();
   if ((version == ARMv5TE) || (version == ARMv6)) {
-    LoadPatchableImmediate(rd, value, cond);
+    if (constant_pool_allowed() &&

[zra, 2015/07/23 22:45:59]

Here: https://codereview.chromium.org//1249623004 it looks like if you use
ObjectPoolWrapper::FindImmediate then you don't need the extra mask+retag.

[regis, 2015/07/23 23:07:31]

Done.

+        // We *could* put constants in the pool in a VM isolate, but it is
+        // simpler to maintain the invariant that the object pool is not used
+        // in the VM isolate.
+        (Isolate::Current() != Dart::vm_isolate())) {
+      // Save the bit that must be masked-off for the SmiTag.
+      int32_t val_smi_tag = value & kSmiTagMask;
+      value &= ~kSmiTagMask;  // Mask off the tag bit.
+      const int32_t offset = Array::element_offset(FindImmediate(value));
+      LoadWordFromPoolOffset(rd, offset - kHeapObjectTag);
+      if (val_smi_tag != 0) {
+        // Add back the tag bit.
+        orr(rd, rd, Operand(val_smi_tag));
+      }
+    } else {
+      LoadPatchableImmediate(rd, value, cond);
+    }
   } else {
     ASSERT(version == ARMv7);
     movw(rd, Utils::Low16Bits(value), cond);
     const uint16_t value_high = Utils::High16Bits(value);
     if (value_high != 0) {
       movt(rd, value_high, cond);
     }
   }
 }
 
@@ skipping 506 matching lines @@
 }
 
 
 void Assembler::CallRuntime(const RuntimeEntry& entry,
                             intptr_t argument_count) {
   entry.Call(this, argument_count);
 }
 
 
 void Assembler::EnterDartFrame(intptr_t frame_size) {
+  ASSERT(!constant_pool_allowed());
   const intptr_t offset = CodeSize();
 
   // Save PC in frame for fast identification of corresponding code.
   // Note that callee-saved registers can be added to the register list.
   EnterFrame((1 << PP) | (1 << FP) | (1 << LR) | (1 << PC), 0);
 
   if (offset != 0) {
     // Adjust saved PC for any intrinsic code that could have been generated
     // before a frame is created. Use PP as temp register.
     ldr(PP, Address(FP, 2 * kWordSize));
     AddImmediate(PP, PP, -offset);
     str(PP, Address(FP, 2 * kWordSize));
   }
 
   // Setup pool pointer for this dart function.
   LoadPoolPointer();
 
   // Reserve space for locals.
   AddImmediate(SP, -frame_size);
 }
 
 
 // On entry to a function compiled for OSR, the caller's frame pointer, the
 // stack locals, and any copied parameters are already in place.  The frame
 // pointer is already set up.  The PC marker is not correct for the
 // optimized function and there may be extra space for spill slots to
 // allocate. We must also set up the pool pointer for the function.
 void Assembler::EnterOsrFrame(intptr_t extra_size) {
+  ASSERT(!constant_pool_allowed());
   // mov(IP, Operand(PC)) loads PC + Instr::kPCReadOffset (8). This may be
   // different from EntryPointToPcMarkerOffset().
   const intptr_t offset =
       CodeSize() + Instr::kPCReadOffset - EntryPointToPcMarkerOffset();
 
   Comment("EnterOsrFrame");
   mov(IP, Operand(PC));
 
   AddImmediate(IP, -offset);
   str(IP, Address(FP, kPcMarkerSlotFromFp * kWordSize));
 
   // Setup pool pointer for this dart function.
   LoadPoolPointer();
 
   AddImmediate(SP, -extra_size);
 }
 
 
 void Assembler::LeaveDartFrame() {
+  // LeaveDartFrame is called from stubs (pp disallowed) and from Dart code (pp
+  // allowed), so there is no point in checking the current value of
+  // constant_pool_allowed().
+  set_constant_pool_allowed(false);
   LeaveFrame((1 << PP) | (1 << FP) | (1 << LR));
   // Adjust SP for PC pushed in EnterDartFrame.
   AddImmediate(SP, kWordSize);
 }
 
 
 void Assembler::EnterStubFrame() {
+  set_constant_pool_allowed(false);
   // Push 0 as saved PC for stub frames.
   mov(IP, Operand(LR));
   mov(LR, Operand(0));
   RegList regs = (1 << PP) | (1 << FP) | (1 << IP) | (1 << LR);
   EnterFrame(regs, 0);
   // Setup pool pointer for this stub.
   LoadPoolPointer();
 }
 
 
 void Assembler::LeaveStubFrame() {
   LeaveFrame((1 << PP) | (1 << FP) | (1 << LR));
+  set_constant_pool_allowed(false);
   // Adjust SP for null PC pushed in EnterStubFrame.
   AddImmediate(SP, kWordSize);
 }
 
 
 void Assembler::LoadAllocationStatsAddress(Register dest,
                                            intptr_t cid,
                                            bool inline_isolate) {
   ASSERT(dest != kNoRegister);
   ASSERT(dest != TMP);
@@ skipping 281 matching lines @@
 
 
 const char* Assembler::FpuRegisterName(FpuRegister reg) {
   ASSERT((0 <= reg) && (reg < kNumberOfFpuRegisters));
   return fpu_reg_names[reg];
 }
 
 }  // namespace dart
 
 #endif  // defined TARGET_ARCH_ARM