[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

1 files changed, 8 insertions, 9 deletions

diff --git a/compiler/utils/arm/assembler_thumb2.cc b/compiler/utils/arm/assembler_thumb2.cc
index e7cf26eee2..75f2b77c96 100644
--- a/compiler/utils/arm/assembler_thumb2.cc
+++ b/compiler/utils/arm/assembler_thumb2.cc
@@ -1638,7 +1638,6 @@ void Thumb2Assembler::EmitBranch(Condition cond, Label* label, bool link, bool x
     // 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 @@ void Thumb2Assembler::EmitBranch(Condition cond, Label* label, bool link, bool x
   } 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 @@ void Thumb2Assembler::Bind(Label* label) {
     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::dmb(DmbOptions flavor) {
 
 
 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