commit f51bc62a1d89a35fabaaf7e766d49502881fd591
author xueliang.zhong <xueliang.zhong@linaro.org> Fri Nov 04 09:23:32 2016 +0000
committer xueliang.zhong <xueliang.zhong@linaro.org> Thu Nov 24 11:39:20 2016 +0000
tree eadb80d9e842476ed599a129a3babad27f7d2167
parent 8f3435981e67e4b78caf0130f81dcd9a87af531e

ARM: VIXL32: Improve codegen on CBZ/CBNZ

This patch improves codegen on CBZ/CBNZ.
CompareAndBranchIfZero/CompareAndBranchIfNonZero are introduced.

These two functions can generate CMP+Bcc or Cbz/Cbnz.
CMP+Bcc are generated by default.
If a hint is given (is_far_target = false) and rn and label
can all fit into Cbz/Cbnz, then Cbz/Cbnz is generated.
Prefer these two interfaces to using vixl32::MacroAssembler::Cbz/Cbnz.
In T32, Cbz/Cbnz instructions have following limitations:
- Far targets, which are over 126 bytes away, are not supported.
- Only low registers can be encoded.
- Backward branches are not supported.

Test: ART_USE_VIXL_ARM_BACKEND=true m test-art-host
Test: ART_USE_VIXL_ARM_BACKEND=true m test-art-target

Change-Id: I5d2ada19ea4f83dab78baf0cf78c72e99e58d946

compiler/utils/arm/assembler_arm_vixl.h

diff --git a/compiler/utils/arm/assembler_arm_vixl.h b/compiler/utils/arm/assembler_arm_vixl.h
index e020628..b4a4abc 100644
--- a/compiler/utils/arm/assembler_arm_vixl.h
+++ b/compiler/utils/arm/assembler_arm_vixl.h
@@ -37,6 +37,25 @@
 namespace art {
 namespace arm {
 
+class ArmVIXLMacroAssembler FINAL : public vixl32::MacroAssembler {
+ public:
+  // The following interfaces can generate CMP+Bcc or Cbz/Cbnz.
+  // CMP+Bcc are generated by default.
+  // If a hint is given (is_far_target = false) and rn and label can all fit into Cbz/Cbnz,
+  // then Cbz/Cbnz is generated.
+  // Prefer following interfaces to using vixl32::MacroAssembler::Cbz/Cbnz.
+  // In T32, Cbz/Cbnz instructions have following limitations:
+  // - Far targets, which are over 126 bytes away, are not supported.
+  // - Only low registers can be encoded.
+  // - Backward branches are not supported.
+  void CompareAndBranchIfZero(vixl32::Register rn,
+                              vixl32::Label* label,
+                              bool is_far_target = true);
+  void CompareAndBranchIfNonZero(vixl32::Register rn,
+                                 vixl32::Label* label,
+                                 bool is_far_target = true);
+};
+
 class ArmVIXLAssembler FINAL : public Assembler {
  private:
   class ArmException;
@@ -48,7 +67,7 @@
   }
 
   virtual ~ArmVIXLAssembler() {}
-  vixl32::MacroAssembler* GetVIXLAssembler() { return &vixl_masm_; }
+  ArmVIXLMacroAssembler* GetVIXLAssembler() { return &vixl_masm_; }
   void FinalizeCode() OVERRIDE;
 
   // Size of generated code.
@@ -117,7 +136,7 @@
 
  private:
   // VIXL assembler.
-  vixl32::MacroAssembler vixl_masm_;
+  ArmVIXLMacroAssembler vixl_masm_;
 };
 
 // Thread register declaration.