Make shadow frame addresses unique.

This CL makes each virtual register's shadow frame address unique in the LLVM
function. Every shadow frame address (gep instructions) are placed right after
allocas to dominate all their uses.

This reduces the number of emitted gep instructions and the memory footprint.

This may also "help" optimization passes to simplify the detection of addresses
in load/store operations where some transformations may be simplified.

Change-Id: I8fe155108db1736c533289962c983caea8c2b63f

1 files changed, 28 insertions, 7 deletions

diff --git a/src/compiler/llvm/gbc_expander.cc b/src/compiler/llvm/gbc_expander.cc
index 9b71694a09..70c54ea839 100644
--- a/src/compiler/llvm/gbc_expander.cc
+++ b/src/compiler/llvm/gbc_expander.cc
@@ -79,6 +79,9 @@ class GBCExpanderPass : public llvm::FunctionPass {
       landing_pad_phi_mapping_;
   llvm::BasicBlock* basic_block_unwind_;
 
+  // Maps each vreg to its shadow frame address.
+  std::vector<llvm::Value*> shadow_frame_vreg_addresses_;
+
   bool changed_;
 
  private:
@@ -375,6 +378,7 @@ bool GBCExpanderPass::runOnFunction(llvm::Function& func) {
   func_ = &func;
   changed_ = false; // Assume unchanged
 
+  shadow_frame_vreg_addresses_.resize(dex_compilation_unit_->GetCodeItem()->registers_size_, NULL);
   basic_blocks_.resize(dex_compilation_unit_->GetCodeItem()->insns_size_in_code_units_);
   basic_block_landing_pads_.resize(dex_compilation_unit_->GetCodeItem()->tries_size_, NULL);
   basic_block_unwind_ = NULL;
@@ -1304,15 +1308,32 @@ void GBCExpanderPass::Expand_AllocaShadowFrame(llvm::Value* num_vregs_value) {
 
 void GBCExpanderPass::Expand_SetVReg(llvm::Value* entry_idx,
                                      llvm::Value* value) {
-  DCHECK(shadow_frame_ != NULL);
+  unsigned vreg_idx = LV2UInt(entry_idx);
+  DCHECK_LT(vreg_idx, dex_compilation_unit_->GetCodeItem()->registers_size_);
 
-  llvm::Value* gep_index[] = {
-    irb_.getInt32(0), // No pointer displacement
-    irb_.getInt32(1), // VRegs
-    entry_idx // Pointer field
-  };
+  llvm::Value* vreg_addr = shadow_frame_vreg_addresses_[vreg_idx];
+  if (UNLIKELY(vreg_addr == NULL)) {
+    DCHECK(shadow_frame_ != NULL);
+
+    llvm::Value* gep_index[] = {
+      irb_.getInt32(0), // No pointer displacement
+      irb_.getInt32(1), // VRegs
+      entry_idx // Pointer field
+    };
 
-  llvm::Value* vreg_addr = irb_.CreateGEP(shadow_frame_, gep_index);
+    // A shadow frame address must dominate every use in the function so we
+    // place it in the entry block right after the allocas.
+    llvm::BasicBlock::iterator first_non_alloca = func_->getEntryBlock().begin();
+    while (llvm::isa<llvm::AllocaInst>(first_non_alloca)) {
+      ++first_non_alloca;
+    }
+
+    llvm::IRBuilderBase::InsertPoint ip = irb_.saveIP();
+    irb_.SetInsertPoint(static_cast<llvm::Instruction*>(first_non_alloca));
+    vreg_addr = irb_.CreateGEP(shadow_frame_, gep_index);
+    shadow_frame_vreg_addresses_[vreg_idx] = vreg_addr;
+    irb_.restoreIP(ip);
+  }
 
   irb_.CreateStore(value,
                    irb_.CreateBitCast(vreg_addr, value->getType()->getPointerTo()),