[RDF] Add option to keep dead phi nodes in DFG

Dead phi nodes are needed for code motion (such as copy propagation),
where a new use would be placed in a location that would be dominated
by a dead phi. Such a transformation is not legal for copy propagation,
and the existence of the phi would prevent it, but if the phi is not
there, it may appear to be valid.

llvm-svn: 267932

1 files changed, 3 insertions, 2 deletions

diff --git a/llvm/lib/Target/Hexagon/RDFGraph.cpp b/llvm/lib/Target/Hexagon/RDFGraph.cpp
index 335e5cb080d..53743e681c1 100644
--- a/llvm/lib/Target/Hexagon/RDFGraph.cpp
+++ b/llvm/lib/Target/Hexagon/RDFGraph.cpp
@@ -919,7 +919,7 @@ NodeAddr<FuncNode*> DataFlowGraph::newFunc(MachineFunction *MF) {
 }
 
 // Build the data flow graph.
-void DataFlowGraph::build() {
+void DataFlowGraph::build(unsigned Options) {
   reset();
   Func = newFunc(&MF);
 
@@ -964,7 +964,8 @@ void DataFlowGraph::build() {
   linkBlockRefs(DM, EA);
 
   // Finally, remove all unused phi nodes.
-  removeUnusedPhis();
+  if (!(Options & BuildOptions::KeepDeadPhis))
+    removeUnusedPhis();
 }
 
 // For each stack in the map DefM, push the delimiter for block B on it.