ART: Register allocation and runtime support for try/catch

This patch completes a series of CLs that add support for try/catch
in the Optimizing compiler. With it, Optimizing can compile all
methods containing try/catch, provided they don't contain catch loops.
Future work will focus on improving performance of the generated code.

SsaLivenessAnalysis was updated to propagate liveness information of
instructions live at catch blocks, and to keep location information on
instructions which may be caught by catch phis.

RegisterAllocator was extended to spill values used after catch, and
to allocate spill slots for catch phis. Catch phis generated for the
same vreg share a spill slot as the raw value must be the same.

Location builders and slow paths were updated to reflect the fact that
throwing an exception may not lead to escaping the method.

Instruction code generators are forbidden from using of implicit null
checks in try blocks as live registers need to be saved before handing
over to the runtime.

CodeGenerator emits a stack map for each catch block, storing locations
of catch phis. CodeInfo and StackMapStream recognize this new type of
stack map and store them separate from other stack maps to avoid dex_pc
conflicts.

After having found the target catch block to deliver an exception to,
QuickExceptionHandler looks up the dex register maps at the throwing
instruction and the catch block and copies the values over to their
respective locations.

The runtime-support approach was selected because it allows for the
best performance in the normal control-flow path, since no propagation
of catch phi values is necessary until the exception is thrown. In
addition, it also greatly simplifies the register allocation phase.

ConstantHoisting was removed from LICMTest because it instantiated
(now abstract) HConstant and was bogus anyway (constants are always in
the entry block).

Change-Id: Ie31038ad8e3ee0c13a5bbbbaf5f0b3e532310e4e

1 files changed, 19 insertions, 8 deletions

diff --git a/compiler/optimizing/ssa_liveness_analysis.cc b/compiler/optimizing/ssa_liveness_analysis.cc
index 0c1831b45f..63635f3127 100644
--- a/compiler/optimizing/ssa_liveness_analysis.cc
+++ b/compiler/optimizing/ssa_liveness_analysis.cc
@@ -186,14 +186,25 @@ void SsaLivenessAnalysis::ComputeLiveRanges() {
     // as live_in.
     for (HBasicBlock* successor : block->GetSuccessors()) {
       live_in->Union(GetLiveInSet(*successor));
-      size_t phi_input_index = successor->GetPredecessorIndexOf(block);
-      for (HInstructionIterator inst_it(successor->GetPhis()); !inst_it.Done(); inst_it.Advance()) {
-        HInstruction* phi = inst_it.Current();
-        HInstruction* input = phi->InputAt(phi_input_index);
-        input->GetLiveInterval()->AddPhiUse(phi, phi_input_index, block);
-        // A phi input whose last user is the phi dies at the end of the predecessor block,
-        // and not at the phi's lifetime position.
-        live_in->SetBit(input->GetSsaIndex());
+      if (successor->IsCatchBlock()) {
+        // Inputs of catch phis will be kept alive through their environment
+        // uses, allowing the runtime to copy their values to the corresponding
+        // catch phi spill slots when an exception is thrown.
+        // The only instructions which may not be recorded in the environments
+        // are constants created by the SSA builder as typed equivalents of
+        // untyped constants from the bytecode, or phis with only such constants
+        // as inputs (verified by SSAChecker). Their raw binary value must
+        // therefore be the same and we only need to keep alive one.
+      } else {
+        size_t phi_input_index = successor->GetPredecessorIndexOf(block);
+        for (HInstructionIterator phi_it(successor->GetPhis()); !phi_it.Done(); phi_it.Advance()) {
+          HInstruction* phi = phi_it.Current();
+          HInstruction* input = phi->InputAt(phi_input_index);
+          input->GetLiveInterval()->AddPhiUse(phi, phi_input_index, block);
+          // A phi input whose last user is the phi dies at the end of the predecessor block,
+          // and not at the phi's lifetime position.
+          live_in->SetBit(input->GetSsaIndex());
+        }
       }
     }