Optimizing: Improve String.equals() thumb intrinsic.

Use SUBS for updating the loop counter and setting the loop
exit condition, so that we don't need to pre-calculate the
bound but still keep the same number of instructions in the
loop.

This reduces the size of boot.oat on Nexus 5 by 8KiB (when
compiled with Optimizing which is not the default yet).

Change-Id: I87d5a128e5e67f4ad177b71c28662d1367170a10

1 files changed, 2 insertions, 5 deletions

diff --git a/compiler/optimizing/intrinsics_arm.cc b/compiler/optimizing/intrinsics_arm.cc
index 806fd7a8f4..48711e6aa0 100644
--- a/compiler/optimizing/intrinsics_arm.cc
+++ b/compiler/optimizing/intrinsics_arm.cc
@@ -989,10 +989,7 @@ void IntrinsicCodeGeneratorARM::VisitStringEquals(HInvoke* invoke) {
   DCHECK_ALIGNED(value_offset, 4);
   static_assert(IsAligned<4>(kObjectAlignment), "String of odd length is not zero padded");
 
-  // temp cannot overflow because we cannot allocate a String object with size 4GiB or greater.
-  __ add(temp, temp, ShifterOperand(temp));
   __ LoadImmediate(temp1, value_offset);
-  __ add(temp, temp, ShifterOperand(value_offset));
 
   // Loop to compare strings 2 characters at a time starting at the front of the string.
   // Ok to do this because strings with an odd length are zero-padded.
@@ -1002,8 +999,8 @@ void IntrinsicCodeGeneratorARM::VisitStringEquals(HInvoke* invoke) {
   __ cmp(out, ShifterOperand(temp2));
   __ b(&return_false, NE);
   __ add(temp1, temp1, ShifterOperand(sizeof(uint32_t)));
-  __ cmp(temp1, ShifterOperand(temp));
-  __ b(&loop, LO);
+  __ subs(temp, temp, ShifterOperand(sizeof(uint32_t) /  sizeof(uint16_t)));
+  __ b(&loop, GT);
 
   // Return true and exit the function.
   // If loop does not result in returning false, we return true.