[globalisel][tablegen] Import signextload and zeroextload.

Allow a pattern rewriter to be installed in CodeGenDAGPatterns and use it to
correct situations where SelectionDAG and GlobalISel disagree on
representation. For example, it would rewrite:
  (sextload:i32 $ptr)<<unindexedload>><<sextload>><<sextloadi16>
to:
  (sext:i32 (load:i16 $ptr)<<unindexedload>>)

I'd have preferred to replace the fragments and have the expansion happen
naturally as part of PatFrag expansion but the type inferencing system can't
cope with loads of types narrower than those mentioned in register classes.
This is because the SDTCisInt's on the sext constrain both the result and
operand to the 'legal' integer types (where legal is defined as 'a register
class can contain the type') which immediately rules the narrower types out.
Several targets (those with only one legal integer type) would then go on to
crash on the SDTCisOpSmallerThanOp<> when it removes all the possible types
for the result of the extend.

Also, improve isObviouslySafeToFold() slightly to automatically return true for
neighbouring instructions. There can't be any re-ordering problems if
re-ordering isn't happenning. We'll need to improve it further to handle
sign/zero-extending loads when the extend and load aren't immediate neighbours
though.

llvm-svn: 317971

3 files changed, 90 insertions, 5 deletions

diff --git a/llvm/utils/TableGen/CodeGenDAGPatterns.cpp b/llvm/utils/TableGen/CodeGenDAGPatterns.cpp
index 3b400c1262e..c07a7267bbe 100644
--- a/llvm/utils/TableGen/CodeGenDAGPatterns.cpp
+++ b/llvm/utils/TableGen/CodeGenDAGPatterns.cpp
@@ -2744,8 +2744,10 @@ void TreePattern::dump() const { print(errs()); }
 // CodeGenDAGPatterns implementation
 //
 
-CodeGenDAGPatterns::CodeGenDAGPatterns(RecordKeeper &R) :
-  Records(R), Target(R), LegalVTS(Target.getLegalValueTypes()) {
+CodeGenDAGPatterns::CodeGenDAGPatterns(RecordKeeper &R,
+                                       PatternRewriterFn PatternRewriter)
+    : Records(R), Target(R), LegalVTS(Target.getLegalValueTypes()),
+      PatternRewriter(PatternRewriter) {
 
   Intrinsics = CodeGenIntrinsicTable(Records, false);
   TgtIntrinsics = CodeGenIntrinsicTable(Records, true);
@@ -3536,6 +3538,8 @@ void CodeGenDAGPatterns::ParseInstructions() {
     TreePattern *I = TheInst.getPattern();
     if (!I) continue;  // No pattern.
 
+    if (PatternRewriter)
+      PatternRewriter(I);
     // FIXME: Assume only the first tree is the pattern. The others are clobber
     // nodes.
     TreePatternNode *Pattern = I->getTree(0);
@@ -3936,6 +3940,8 @@ void CodeGenDAGPatterns::ParsePatterns() {
         Temp.getOnlyTree()->hasPossibleType()) {
       ListInit *Preds = CurPattern->getValueAsListInit("Predicates");
       int Complexity = CurPattern->getValueAsInt("AddedComplexity");
+      if (PatternRewriter)
+        PatternRewriter(Pattern);
       AddPatternToMatch(
           Pattern,
           PatternToMatch(
diff --git a/llvm/utils/TableGen/CodeGenDAGPatterns.h b/llvm/utils/TableGen/CodeGenDAGPatterns.h
index 1f7e9fb98d3..d3bb99a5a8f 100644
--- a/llvm/utils/TableGen/CodeGenDAGPatterns.h
+++ b/llvm/utils/TableGen/CodeGenDAGPatterns.h
@@ -25,6 +25,7 @@
 #include "llvm/Support/MathExtras.h"
 #include <algorithm>
 #include <array>
+#include <functional>
 #include <map>
 #include <set>
 #include <vector>
@@ -780,6 +781,7 @@ public:
   const std::vector<TreePatternNode*> &getTrees() const { return Trees; }
   unsigned getNumTrees() const { return Trees.size(); }
   TreePatternNode *getTree(unsigned i) const { return Trees[i]; }
+  void setTree(unsigned i, TreePatternNode *Tree) { Trees[i] = Tree; }
   TreePatternNode *getOnlyTree() const {
     assert(Trees.size() == 1 && "Doesn't have exactly one pattern!");
     return Trees[0];
@@ -1029,8 +1031,12 @@ class CodeGenDAGPatterns {
 
   TypeSetByHwMode LegalVTS;
 
+  using PatternRewriterFn = std::function<void (TreePattern *)>;
+  PatternRewriterFn PatternRewriter;
+
 public:
-  CodeGenDAGPatterns(RecordKeeper &R);
+  CodeGenDAGPatterns(RecordKeeper &R,
+                     PatternRewriterFn PatternRewriter = nullptr);
 
   CodeGenTarget &getTargetInfo() { return Target; }
   const CodeGenTarget &getTargetInfo() const { return Target; }
diff --git a/llvm/utils/TableGen/GlobalISelEmitter.cpp b/llvm/utils/TableGen/GlobalISelEmitter.cpp
index 08649d7f9b5..8a0d625ca44 100644
--- a/llvm/utils/TableGen/GlobalISelEmitter.cpp
+++ b/llvm/utils/TableGen/GlobalISelEmitter.cpp
@@ -2356,6 +2356,9 @@ private:
   Expected<RuleMatcher> runOnPattern(const PatternToMatch &P);
 
   void declareSubtargetFeature(Record *Predicate);
+
+  TreePatternNode *fixupPatternNode(TreePatternNode *N);
+  void fixupPatternTrees(TreePattern *P);
 };
 
 void GlobalISelEmitter::gatherNodeEquivs() {
@@ -2377,8 +2380,8 @@ Record *GlobalISelEmitter::findNodeEquiv(Record *N) const {
 }
 
 GlobalISelEmitter::GlobalISelEmitter(RecordKeeper &RK)
-    : RK(RK), CGP(RK), Target(CGP.getTargetInfo()),
-      CGRegs(RK, Target.getHwModes()) {}
+    : RK(RK), CGP(RK, [&](TreePattern *P) { fixupPatternTrees(P); }),
+      Target(CGP.getTargetInfo()), CGRegs(RK, Target.getHwModes()) {}
 
 //===- Emitter ------------------------------------------------------------===//
 
@@ -3233,6 +3236,7 @@ void GlobalISelEmitter::run(raw_ostream &OS) {
   // Look through the SelectionDAG patterns we found, possibly emitting some.
   for (const PatternToMatch &Pat : CGP.ptms()) {
     ++NumPatternTotal;
+
     auto MatcherOrErr = runOnPattern(Pat);
 
     // The pattern analysis can fail, indicating an unsupported pattern.
@@ -3483,6 +3487,75 @@ void GlobalISelEmitter::declareSubtargetFeature(Record *Predicate) {
         Predicate, SubtargetFeatureInfo(Predicate, SubtargetFeatures.size()));
 }
 
+TreePatternNode *GlobalISelEmitter::fixupPatternNode(TreePatternNode *N) {
+  if (!N->isLeaf()) {
+    for (unsigned I = 0, E = N->getNumChildren(); I < E; ++I) {
+      TreePatternNode *OrigChild = N->getChild(I);
+      TreePatternNode *NewChild = fixupPatternNode(OrigChild);
+      if (OrigChild != NewChild)
+        N->setChild(I, NewChild);
+    }
+
+    if (N->getOperator()->getName() == "ld") {
+      // If it's a signext-load we need to adapt the pattern slightly. We need
+      // to split the node into (sext (ld ...)), remove the <<signext>> predicate,
+      // and then apply the <<signextTY>> predicate by updating the result type
+      // of the load.
+      //
+      // For example:
+      //   (ld:[i32] [iPTR])<<unindexed>><<signext>><<signexti16>>
+      // must be transformed into:
+      //   (sext:[i32] (ld:[i16] [iPTR])<<unindexed>>)
+      //
+      // Likewise for zeroext-load.
+
+      std::vector<TreePredicateFn> Predicates;
+      bool IsSignExtLoad = false;
+      bool IsZeroExtLoad = false;
+      Record *MemVT = nullptr;
+      for (const auto &P : N->getPredicateFns()) {
+        if (P.isLoad() && P.isSignExtLoad()) {
+          IsSignExtLoad = true;
+          continue;
+        }
+        if (P.isLoad() && P.isZeroExtLoad()) {
+          IsZeroExtLoad = true;
+          continue;
+        }
+        if (P.isLoad() && P.getMemoryVT()) {
+          MemVT = P.getMemoryVT();
+          continue;
+        }
+        Predicates.push_back(P);
+      }
+
+      if ((IsSignExtLoad || IsZeroExtLoad) && MemVT) {
+        assert(((IsSignExtLoad && !IsZeroExtLoad) ||
+                (!IsSignExtLoad && IsZeroExtLoad)) &&
+               "IsSignExtLoad and IsZeroExtLoad are mutually exclusive");
+        TreePatternNode *Ext = new TreePatternNode(
+            RK.getDef(IsSignExtLoad ? "sext" : "zext"), {N}, 1);
+        Ext->setType(0, N->getType(0));
+        N->clearPredicateFns();
+        N->setPredicateFns(Predicates);
+        N->setType(0, getValueType(MemVT));
+        return Ext;
+      }
+    }
+  }
+
+  return N;
+}
+
+void GlobalISelEmitter::fixupPatternTrees(TreePattern *P) {
+  for (unsigned I = 0, E = P->getNumTrees(); I < E; ++I) {
+    TreePatternNode *OrigTree = P->getTree(I);
+    TreePatternNode *NewTree = fixupPatternNode(OrigTree);
+    if (OrigTree != NewTree)
+      P->setTree(I, NewTree);
+  }
+}
+
 } // end anonymous namespace
 
 //===----------------------------------------------------------------------===//