Fix a bug in the SSA builder.

The build would leave behind phis with incompatible input types
(for example float and int). We need another dead phi run after
the type propagation to ensure all such phis are dead.

Change-Id: I6ef1da725c7d4a1ebaf6b52dd7eb0c7bacd261b2

1 files changed, 12 insertions, 8 deletions

diff --git a/compiler/optimizing/ssa_builder.cc b/compiler/optimizing/ssa_builder.cc
index 1a8e784..ba11e90 100644
--- a/compiler/optimizing/ssa_builder.cc
+++ b/compiler/optimizing/ssa_builder.cc
@@ -199,9 +199,9 @@ void SsaBuilder::BuildSsa() {
   // our code generator will complain if the inputs of a phi do not have the same
   // type. The marking allows the type propagation to know which phis it needs
   // to handle. We mark but do not eliminate: the elimination will be done in
-  // step 8).
-  SsaDeadPhiElimination dead_phis(GetGraph());
-  dead_phis.MarkDeadPhis();
+  // step 9).
+  SsaDeadPhiElimination dead_phis_for_type_propagation(GetGraph());
+  dead_phis_for_type_propagation.MarkDeadPhis();
 
   // 4) Propagate types of phis. At this point, phis are typed void in the general
   // case, or float/double/reference when we created an equivalent phi. So we
@@ -209,7 +209,11 @@ void SsaBuilder::BuildSsa() {
   PrimitiveTypePropagation type_propagation(GetGraph());
   type_propagation.Run();
 
-  // 5) Now that the graph is correclty typed, we can get rid of redundant phis.
+  // 5) Mark dead phis again. Steph 4) may have introduced new phis.
+  SsaDeadPhiElimination dead_phis(GetGraph());
+  dead_phis.MarkDeadPhis();
+
+  // 6) Now that the graph is correclty typed, we can get rid of redundant phis.
   // Note that we cannot do this phase before type propagation, otherwise
   // we could get rid of phi equivalents, whose presence is a requirement for the
   // type propagation phase. Note that this is to satisfy statement (a) of the
@@ -217,7 +221,7 @@ void SsaBuilder::BuildSsa() {
   SsaRedundantPhiElimination redundant_phi(GetGraph());
   redundant_phi.Run();
 
-  // 6) Make sure environments use the right phi "equivalent": a phi marked dead
+  // 7) Make sure environments use the right phi "equivalent": a phi marked dead
   // can have a phi equivalent that is not dead. We must therefore update
   // all environment uses of the dead phi to use its equivalent. Note that there
   // can be multiple phis for the same Dex register that are live (for example
@@ -244,7 +248,7 @@ void SsaBuilder::BuildSsa() {
     }
   }
 
-  // 7) Deal with phis to guarantee liveness of phis in case of a debuggable
+  // 8) Deal with phis to guarantee liveness of phis in case of a debuggable
   // application. This is for satisfying statement (c) of the SsaBuilder
   // (see ssa_builder.h).
   if (GetGraph()->IsDebuggable()) {
@@ -252,7 +256,7 @@ void SsaBuilder::BuildSsa() {
     dead_phi_handler.Run();
   }
 
-  // 8) Now that the right phis are used for the environments, and we
+  // 9) Now that the right phis are used for the environments, and we
   // have potentially revive dead phis in case of a debuggable application,
   // we can eliminate phis we do not need. Regardless of the debuggable status,
   // this phase is necessary for statement (b) of the SsaBuilder (see ssa_builder.h),
@@ -260,7 +264,7 @@ void SsaBuilder::BuildSsa() {
   // input types.
   dead_phis.EliminateDeadPhis();
 
-  // 9) Clear locals.
+  // 10) Clear locals.
   for (HInstructionIterator it(GetGraph()->GetEntryBlock()->GetInstructions());
        !it.Done();
        it.Advance()) {