[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, 8 insertions, 1 deletions

diff --git a/llvm/lib/Target/Hexagon/RDFGraph.h b/llvm/lib/Target/Hexagon/RDFGraph.h
index 1de50d7d987..43eeb483173 100644
--- a/llvm/lib/Target/Hexagon/RDFGraph.h
+++ b/llvm/lib/Target/Hexagon/RDFGraph.h
@@ -287,6 +287,13 @@ namespace rdf {
     }
   };
 
+  struct BuildOptions {
+    enum : unsigned {
+      None          = 0x00,
+      KeepDeadPhis  = 0x01,   // Do not remove dead phis during build.
+    };
+  };
+
   template <typename T> struct NodeAddr {
     NodeAddr() : Addr(nullptr), Id(0) {}
     NodeAddr(T A, NodeId I) : Addr(A), Id(I) {}
@@ -677,7 +684,7 @@ namespace rdf {
 
     typedef std::map<RegisterRef,DefStack> DefStackMap;
 
-    void build();
+    void build(unsigned Options = BuildOptions::None);
     void pushDefs(NodeAddr<InstrNode*> IA, DefStackMap &DM);
     void markBlock(NodeId B, DefStackMap &DefM);
     void releaseBlock(NodeId B, DefStackMap &DefM);