[Optimizing] Thumb2 assembler: use 16bits branches when we can.
We cannot relocate branches, but we can at least encode branches
on 16bits when the target is known.
Change-Id: Icb6116ed974fc97e03622ac80d914c2c06f4cba2
diff --git a/compiler/optimizing/code_generator_arm.cc b/compiler/optimizing/code_generator_arm.cc
index 7b37f74..1c76630 100644
--- a/compiler/optimizing/code_generator_arm.cc
+++ b/compiler/optimizing/code_generator_arm.cc
@@ -391,7 +391,7 @@
location_builder_(graph, this),
instruction_visitor_(graph, this),
move_resolver_(graph->GetArena(), this),
- assembler_(true),
+ assembler_(false /* can_relocate_branches */),
isa_features_(isa_features) {
// Save the PC register to mimic Quick.
AddAllocatedRegister(Location::RegisterLocation(PC));
diff --git a/compiler/utils/arm/assembler_thumb2.cc b/compiler/utils/arm/assembler_thumb2.cc
index e7cf26e..75f2b77 100644
--- a/compiler/utils/arm/assembler_thumb2.cc
+++ b/compiler/utils/arm/assembler_thumb2.cc
@@ -1638,7 +1638,6 @@
// branch the size may change if it so happens that other branches change size that change
// the distance to the target and that distance puts this branch over the limit for 16 bits.
if (size == Branch::k16Bit) {
- DCHECK(!force_32bit_branches_);
Emit16(0); // Space for a 16 bit branch.
} else {
Emit32(0); // Space for a 32 bit branch.
@@ -1646,7 +1645,7 @@
} else {
// Branch is to an unbound label. Emit space for it.
uint16_t branch_id = AddBranch(branch_type, pc, cond); // Unresolved branch.
- if (force_32bit_branches_ || force_32bit_) {
+ if (!CanRelocateBranches() || force_32bit_) {
Emit16(static_cast<uint16_t>(label->position_)); // Emit current label link.
Emit16(0); // another 16 bits.
} else {
@@ -2282,7 +2281,7 @@
uint32_t branch_location = branch->GetLocation();
uint16_t next = buffer_.Load<uint16_t>(branch_location); // Get next in chain.
if (changed) {
- DCHECK(!force_32bit_branches_);
+ DCHECK(CanRelocateBranches());
MakeHoleForBranch(branch->GetLocation(), 2);
if (branch->IsCompareAndBranch()) {
// A cbz/cbnz instruction has changed size. There is no valid encoding for
@@ -2742,21 +2741,21 @@
void Thumb2Assembler::CompareAndBranchIfZero(Register r, Label* label) {
- if (force_32bit_branches_) {
+ if (CanRelocateBranches()) {
+ cbz(r, label);
+ } else {
cmp(r, ShifterOperand(0));
b(label, EQ);
- } else {
- cbz(r, label);
}
}
void Thumb2Assembler::CompareAndBranchIfNonZero(Register r, Label* label) {
- if (force_32bit_branches_) {
+ if (CanRelocateBranches()) {
+ cbnz(r, label);
+ } else {
cmp(r, ShifterOperand(0));
b(label, NE);
- } else {
- cbnz(r, label);
}
}
} // namespace arm
diff --git a/compiler/utils/arm/assembler_thumb2.h b/compiler/utils/arm/assembler_thumb2.h
index 17eae8b..90d489f 100644
--- a/compiler/utils/arm/assembler_thumb2.h
+++ b/compiler/utils/arm/assembler_thumb2.h
@@ -31,8 +31,8 @@
class Thumb2Assembler FINAL : public ArmAssembler {
public:
- explicit Thumb2Assembler(bool force_32bit_branches = false)
- : force_32bit_branches_(force_32bit_branches),
+ explicit Thumb2Assembler(bool can_relocate_branches = true)
+ : can_relocate_branches_(can_relocate_branches),
force_32bit_(false),
it_cond_index_(kNoItCondition),
next_condition_(AL) {
@@ -52,8 +52,8 @@
return force_32bit_;
}
- bool IsForced32BitBranches() const {
- return force_32bit_branches_;
+ bool CanRelocateBranches() const {
+ return can_relocate_branches_;
}
void FinalizeInstructions(const MemoryRegion& region) OVERRIDE {
@@ -439,8 +439,12 @@
void EmitShift(Register rd, Register rm, Shift shift, uint8_t amount, bool setcc = false);
void EmitShift(Register rd, Register rn, Shift shift, Register rm, bool setcc = false);
- bool force_32bit_branches_; // Force the assembler to use 32 bit branch instructions.
- bool force_32bit_; // Force the assembler to use 32 bit thumb2 instructions.
+ // Whether the assembler can relocate branches. If false, unresolved branches will be
+ // emitted on 32bits.
+ bool can_relocate_branches_;
+
+ // Force the assembler to use 32 bit thumb2 instructions.
+ bool force_32bit_;
// IfThen conditions. Used to check that conditional instructions match the preceding IT.
Condition it_conditions_[4];
@@ -556,12 +560,21 @@
// size of the branch to change return true. Otherwise return false.
bool Resolve(uint32_t target) {
target_ = target;
- Size newsize = CalculateSize();
- if (size_ != newsize) {
- size_ = newsize;
- return true;
+ if (assembler_->CanRelocateBranches()) {
+ Size new_size = CalculateSize();
+ if (size_ != new_size) {
+ size_ = new_size;
+ return true;
+ }
+ return false;
+ } else {
+ if (kIsDebugBuild) {
+ Size new_size = CalculateSize();
+ // Check that the size has not increased.
+ DCHECK(!(new_size == k32Bit && size_ == k16Bit));
+ }
+ return false;
}
- return false;
}
// Move a cbz/cbnz branch. This is always forward.
@@ -577,6 +590,7 @@
// size of the branch instruction. It returns true if the branch
// has changed size.
bool Relocate(uint32_t oldlocation, int32_t delta) {
+ DCHECK(assembler_->CanRelocateBranches());
if (location_ > oldlocation) {
location_ += delta;
}
@@ -589,9 +603,9 @@
}
// Calculate the new size.
- Size newsize = CalculateSize();
- if (size_ != newsize) {
- size_ = newsize;
+ Size new_size = CalculateSize();
+ if (size_ != new_size) {
+ size_ = new_size;
return true;
}
return false;
@@ -633,15 +647,13 @@
private:
// Calculate the size of the branch instruction based on its type and offset.
Size CalculateSize() const {
- if (assembler_->IsForced32BitBranches()) {
- return k32Bit;
- }
if (target_ == kUnresolved) {
if (assembler_->IsForced32Bit() && (type_ == kUnconditional || type_ == kConditional)) {
return k32Bit;
}
- return k16Bit;
+ return assembler_->CanRelocateBranches() ? k16Bit : k32Bit;
}
+ // When the target is resolved, we know the best encoding for it.
int32_t delta = target_ - location_ - 4;
if (delta < 0) {
delta = -delta;
