commit ef4a6564254012b7ba00d6310521b1c0d938bdac
author Logan Chien <loganchien@google.com> Tue Apr 24 18:02:24 2012 +0800
committer Shih-wei Liao <sliao@google.com> Tue May 01 22:15:07 2012 -0700
tree f8baca905b3ea99e3b116d99833ea520448552e8
parent 6ee997605c9f5a029250e50330ac764d1eb8112a

Remove unnecessary zero-initializer.

Dex verifier will guarantee that a Dalvik register will be
initialized before any usage.  So we don't have to generate
the code to initialize them to 0 after allocation.

NOTE: We wrote the zero-initializer for historical reason.
There was a bug in the implementation of SHL, SHR, USHR,
and result in undef value after optimization.  Since we
have found the bug, and we don't get undef any more, it's
time to remove these zero-initializer to save code size
and run time.

Change-Id: I0375af3bed08495f6743699c7a72c295cad71dfa

src/compiler_llvm/method_compiler.cc

diff --git a/src/compiler_llvm/method_compiler.cc b/src/compiler_llvm/method_compiler.cc
index 1253d37..52807e3 100644
--- a/src/compiler_llvm/method_compiler.cc
+++ b/src/compiler_llvm/method_compiler.cc
@@ -63,7 +63,7 @@
     irb_(*cunit->GetIRBuilder()), func_(NULL), retval_reg_(NULL),
     basic_block_stack_overflow_(NULL),
     basic_block_reg_alloca_(NULL), basic_block_shadow_frame_alloca_(NULL),
-    basic_block_reg_zero_init_(NULL), basic_block_reg_arg_init_(NULL),
+    basic_block_reg_arg_init_(NULL),
     basic_blocks_(code_item_->insns_size_in_code_units_),
     basic_block_landing_pads_(code_item_->tries_size_, NULL),
     basic_block_unwind_(NULL), basic_block_unreachable_(NULL),
@@ -148,9 +148,6 @@
   basic_block_shadow_frame_alloca_ =
     llvm::BasicBlock::Create(*context_, "prologue.shadowframe", func_);
 
-  basic_block_reg_zero_init_ =
-    llvm::BasicBlock::Create(*context_, "prologue.zeroinit", func_);
-
   basic_block_reg_arg_init_ =
     llvm::BasicBlock::Create(*context_, "prologue.arginit", func_);
 
@@ -235,9 +232,6 @@
   irb_.CreateBr(basic_block_shadow_frame_alloca_);
 
   irb_.SetInsertPoint(basic_block_shadow_frame_alloca_);
-  irb_.CreateBr(basic_block_reg_zero_init_);
-
-  irb_.SetInsertPoint(basic_block_reg_zero_init_);
   irb_.CreateBr(basic_block_reg_arg_init_);
 }
 
@@ -3926,18 +3920,12 @@
     irb_.SetInsertPoint(basic_block_reg_alloca_);
     reg_addr = irb_.CreateAlloca(irb_.getJIntTy(), 0,
                                  StringPrintf("r%u", reg_idx));
-
-    irb_.SetInsertPoint(basic_block_reg_zero_init_);
-    irb_.CreateStore(irb_.getJInt(0), reg_addr);
     break;
 
   case kRegCat2:
     irb_.SetInsertPoint(basic_block_reg_alloca_);
     reg_addr = irb_.CreateAlloca(irb_.getJLongTy(), 0,
                                  StringPrintf("w%u", reg_idx));
-
-    irb_.SetInsertPoint(basic_block_reg_zero_init_);
-    irb_.CreateStore(irb_.getJLong(0), reg_addr);
     break;
 
   case kRegObject:
@@ -3952,9 +3940,6 @@
 
       reg_addr = irb_.CreateGEP(shadow_frame_, gep_index,
                                 StringPrintf("p%u", reg_idx));
-
-      irb_.SetInsertPoint(basic_block_reg_zero_init_);
-      irb_.CreateStore(irb_.getJNull(), reg_addr);
     }
     break;
 

src/compiler_llvm/method_compiler.h

diff --git a/src/compiler_llvm/method_compiler.h b/src/compiler_llvm/method_compiler.h
index 7dded33..d5a4374 100644
--- a/src/compiler_llvm/method_compiler.h
+++ b/src/compiler_llvm/method_compiler.h
@@ -456,7 +456,6 @@
   llvm::BasicBlock* basic_block_stack_overflow_;
   llvm::BasicBlock* basic_block_reg_alloca_;
   llvm::BasicBlock* basic_block_shadow_frame_alloca_;
-  llvm::BasicBlock* basic_block_reg_zero_init_;
   llvm::BasicBlock* basic_block_reg_arg_init_;
   std::vector<llvm::BasicBlock*> basic_blocks_;