commit 9522af985466b2a05ef5cdede0808777dea7236e
author Andreas Gampe <agampe@google.com> Mon Jul 14 20:16:59 2014 -0700
committer Andreas Gampe <agampe@google.com> Tue Jul 15 10:23:03 2014 -0700
tree cdc03acc6700eac3760d8f1eda312a8769d516ea
parent 635561b86ac03f5562bdb779baa6db12f31b3cae

ART: Squash a cmp w/ zero and b.ls to cbz (ARM/ARM64)

In case of array bounds checks at constant index 0 we generate a
compare and a branch. Squash into a cbz.

Change-Id: I1c6a6e37a7a2356b2c4580a3387cedb55436e251

compiler/dex/quick/arm/int_arm.cc

diff --git a/compiler/dex/quick/arm/int_arm.cc b/compiler/dex/quick/arm/int_arm.cc
index f4ea592..2fcc3a5 100644
--- a/compiler/dex/quick/arm/int_arm.cc
+++ b/compiler/dex/quick/arm/int_arm.cc
@@ -341,7 +341,7 @@
  * is responsible for setting branch target field.
  */
 LIR* ArmMir2Lir::OpCmpImmBranch(ConditionCode cond, RegStorage reg, int check_value, LIR* target) {
-  LIR* branch;
+  LIR* branch = nullptr;
   ArmConditionCode arm_cond = ArmConditionEncoding(cond);
   /*
    * A common use of OpCmpImmBranch is for null checks, and using the Thumb 16-bit
@@ -354,14 +354,22 @@
    */
   bool skip = ((target != NULL) && (target->opcode == kPseudoThrowTarget));
   skip &= ((cu_->code_item->insns_size_in_code_units_ - current_dalvik_offset_) > 64);
-  if (!skip && reg.Low8() && (check_value == 0) &&
-     ((arm_cond == kArmCondEq) || (arm_cond == kArmCondNe))) {
-    branch = NewLIR2((arm_cond == kArmCondEq) ? kThumb2Cbz : kThumb2Cbnz,
-                     reg.GetReg(), 0);
-  } else {
+  if (!skip && reg.Low8() && (check_value == 0)) {
+    if (arm_cond == kArmCondEq || arm_cond == kArmCondNe) {
+      branch = NewLIR2((arm_cond == kArmCondEq) ? kThumb2Cbz : kThumb2Cbnz,
+                       reg.GetReg(), 0);
+    } else if (arm_cond == kArmCondLs) {
+      // kArmCondLs is an unsigned less or equal. A comparison r <= 0 is then the same as cbz.
+      // This case happens for a bounds check of array[0].
+      branch = NewLIR2(kThumb2Cbz, reg.GetReg(), 0);
+    }
+  }
+
+  if (branch == nullptr) {
     OpRegImm(kOpCmp, reg, check_value);
     branch = NewLIR2(kThumbBCond, 0, arm_cond);
   }
+
   branch->target = target;
   return branch;
 }

compiler/dex/quick/arm64/int_arm64.cc

diff --git a/compiler/dex/quick/arm64/int_arm64.cc b/compiler/dex/quick/arm64/int_arm64.cc
index 2650892..6dc4a7a 100644
--- a/compiler/dex/quick/arm64/int_arm64.cc
+++ b/compiler/dex/quick/arm64/int_arm64.cc
@@ -269,16 +269,27 @@
  */
 LIR* Arm64Mir2Lir::OpCmpImmBranch(ConditionCode cond, RegStorage reg, int check_value,
                                   LIR* target) {
-  LIR* branch;
+  LIR* branch = nullptr;
   ArmConditionCode arm_cond = ArmConditionEncoding(cond);
-  if (check_value == 0 && (arm_cond == kArmCondEq || arm_cond == kArmCondNe)) {
-    ArmOpcode opcode = (arm_cond == kArmCondEq) ? kA64Cbz2rt : kA64Cbnz2rt;
-    ArmOpcode wide = reg.Is64Bit() ? WIDE(0) : UNWIDE(0);
-    branch = NewLIR2(opcode | wide, reg.GetReg(), 0);
-  } else {
+  if (check_value == 0) {
+    if (arm_cond == kArmCondEq || arm_cond == kArmCondNe) {
+      ArmOpcode opcode = (arm_cond == kArmCondEq) ? kA64Cbz2rt : kA64Cbnz2rt;
+      ArmOpcode wide = reg.Is64Bit() ? WIDE(0) : UNWIDE(0);
+      branch = NewLIR2(opcode | wide, reg.GetReg(), 0);
+    } else if (arm_cond == kArmCondLs) {
+      // kArmCondLs is an unsigned less or equal. A comparison r <= 0 is then the same as cbz.
+      // This case happens for a bounds check of array[0].
+      ArmOpcode opcode = kA64Cbz2rt;
+      ArmOpcode wide = reg.Is64Bit() ? WIDE(0) : UNWIDE(0);
+      branch = NewLIR2(opcode | wide, reg.GetReg(), 0);
+    }
+  }
+
+  if (branch == nullptr) {
     OpRegImm(kOpCmp, reg, check_value);
     branch = NewLIR2(kA64B2ct, arm_cond, 0);
   }
+
   branch->target = target;
   return branch;
 }