Add an OutPatFrag TableGen class

Unfortunately, it is currently impossible to use a PatFrag as part of an output
pattern (the part of the pattern that has instructions in it) in TableGen.
Looking at the current implementation, this was clearly intended to work (there
is already code in place to expand patterns in the output DAG), but is
currently broken by the baked-in type-checking assumption and the order in which
the pattern fragments are processed (output pattern fragments need to be
processed after the instruction definitions are processed).

Fixing this is fairly simple, but requires some way of differentiating output
patterns from the existing input patterns. The simplest way to handle this
seems to be to create a subclass of PatFrag, and so that's what I've done here.

As a simple example, this allows us to write:

def crnot : OutPatFrag<(ops node:$in),
                       (CRNOR $in, $in)>;

def       : Pat<(not i1:$in),
                (crnot $in)>;

which captures the core use case: handling of repeated subexpressions inside
of complicated output patterns.

This will be used by an upcoming commit to the PowerPC backend.

llvm-svn: 202450

llvm/include/llvm/Target/TargetSelectionDAG.td

@@ -560,6 +560,12 @@ class PatFrag<dag ops, dag frag, code pred = [{}],
   SDNodeXForm OperandTransform = xform;
 }
 
+// OutPatFrag is a pattern fragment that is used as part of an output pattern
+// (not an input pattern). These do not have predicates or transforms, but are
+// used to avoid repeated subexpressions in output patterns.
+class OutPatFrag<dag ops, dag frag>
+ : PatFrag<ops, frag, [{}], NOOP_SDNodeXForm>;
+
 // PatLeaf's are pattern fragments that have no operands.  This is just a helper
 // to define immediates and other common things concisely.
 class PatLeaf<dag frag, code pred = [{}], SDNodeXForm xform = NOOP_SDNodeXForm>

llvm/utils/TableGen/CodeGenDAGPatterns.cpp

@@ -1232,8 +1232,10 @@ SubstituteFormalArguments(std::map<std::string, TreePatternNode*> &ArgMap) {
     TreePatternNode *Child = getChild(i);
     if (Child->isLeaf()) {
       Init *Val = Child->getLeafValue();
-      if (isa<DefInit>(Val) &&
-          cast<DefInit>(Val)->getDef()->getName() == "node") {
+      // Note that, when substituting into an output pattern, Val might be an
+      // UnsetInit.
+      if (isa<UnsetInit>(Val) || (isa<DefInit>(Val) &&
+          cast<DefInit>(Val)->getDef()->getName() == "node")) {
         // We found a use of a formal argument, replace it with its value.
         TreePatternNode *NewChild = ArgMap[Child->getName()];
         assert(NewChild && "Couldn't find formal argument!");
@@ -2135,6 +2137,7 @@ CodeGenDAGPatterns::CodeGenDAGPatterns(RecordKeeper &R) :
   ParsePatternFragments();
   ParseDefaultOperands();
   ParseInstructions();
+  ParsePatternFragments(/*OutFrags*/true);
   ParsePatterns();
 
   // Generate variants.  For example, commutative patterns can match
@@ -2208,13 +2211,18 @@ void CodeGenDAGPatterns::ParseComplexPatterns() {
 /// inline fragments together as necessary, so that there are no references left
 /// inside a pattern fragment to a pattern fragment.
 ///
-void CodeGenDAGPatterns::ParsePatternFragments() {
+void CodeGenDAGPatterns::ParsePatternFragments(bool OutFrags) {
   std::vector<Record*> Fragments = Records.getAllDerivedDefinitions("PatFrag");
 
   // First step, parse all of the fragments.
   for (unsigned i = 0, e = Fragments.size(); i != e; ++i) {
+    if (OutFrags != Fragments[i]->isSubClassOf("OutPatFrag"))
+      continue;
+
     DagInit *Tree = Fragments[i]->getValueAsDag("Fragment");
-    TreePattern *P = new TreePattern(Fragments[i], Tree, true, *this);
+    TreePattern *P =
+      new TreePattern(Fragments[i], Tree,
+                      !Fragments[i]->isSubClassOf("OutPatFrag"), *this);
     PatternFragments[Fragments[i]] = P;
 
     // Validate the argument list, converting it to set, to discard duplicates.
@@ -2270,6 +2278,9 @@ void CodeGenDAGPatterns::ParsePatternFragments() {
   // Now that we've parsed all of the tree fragments, do a closure on them so
   // that there are not references to PatFrags left inside of them.
   for (unsigned i = 0, e = Fragments.size(); i != e; ++i) {
+    if (OutFrags != Fragments[i]->isSubClassOf("OutPatFrag"))
+      continue;
+
     TreePattern *ThePat = PatternFragments[Fragments[i]];
     ThePat->InlinePatternFragments();
 

llvm/utils/TableGen/CodeGenDAGPatterns.h

@@ -809,7 +809,7 @@ private:
   void ParseNodeInfo();
   void ParseNodeTransforms();
   void ParseComplexPatterns();
-  void ParsePatternFragments();
+  void ParsePatternFragments(bool OutFrags = false);
   void ParseDefaultOperands();
   void ParseInstructions();
   void ParsePatterns();