InstCombine: FoldOrOfICmps harder

We may be in a situation where the icmps might not be near each other in
a tree of or instructions.  Try to dig out related compare instructions
and see if they combine.

N.B.  This won't fire on deep trees of compares because rewritting the
tree might end up creating a net increase of IR.  We may have to resort
to something more sophisticated if this is a real problem.

llvm-svn: 222928

1 files changed, 25 insertions, 2 deletions

diff --git a/llvm/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp b/llvm/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp
index 55ebcedf944..60b859fc149 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp
@@ -2305,11 +2305,34 @@ Instruction *InstCombiner::visitOr(BinaryOperator &I) {
   if (SwappedForXor)
     std::swap(Op0, Op1);
 
-  if (ICmpInst *RHS = dyn_cast<ICmpInst>(I.getOperand(1)))
-    if (ICmpInst *LHS = dyn_cast<ICmpInst>(I.getOperand(0)))
+  {
+    ICmpInst *LHS = dyn_cast<ICmpInst>(Op0);
+    ICmpInst *RHS = dyn_cast<ICmpInst>(Op1);
+    if (LHS && RHS)
       if (Value *Res = FoldOrOfICmps(LHS, RHS, &I))
         return ReplaceInstUsesWith(I, Res);
 
+    // TODO: Make this recursive; it's a little tricky because an arbitrary
+    // number of 'or' instructions might have to be created.
+    Value *X, *Y;
+    if (LHS && match(Op1, m_OneUse(m_Or(m_Value(X), m_Value(Y))))) {
+      if (auto *Cmp = dyn_cast<ICmpInst>(X))
+        if (Value *Res = FoldOrOfICmps(LHS, Cmp, &I))
+          return ReplaceInstUsesWith(I, Builder->CreateOr(Res, Y));
+      if (auto *Cmp = dyn_cast<ICmpInst>(Y))
+        if (Value *Res = FoldOrOfICmps(LHS, Cmp, &I))
+          return ReplaceInstUsesWith(I, Builder->CreateOr(Res, X));
+    }
+    if (RHS && match(Op0, m_OneUse(m_Or(m_Value(X), m_Value(Y))))) {
+      if (auto *Cmp = dyn_cast<ICmpInst>(X))
+        if (Value *Res = FoldOrOfICmps(Cmp, RHS, &I))
+          return ReplaceInstUsesWith(I, Builder->CreateOr(Res, Y));
+      if (auto *Cmp = dyn_cast<ICmpInst>(Y))
+        if (Value *Res = FoldOrOfICmps(Cmp, RHS, &I))
+          return ReplaceInstUsesWith(I, Builder->CreateOr(Res, X));
+    }
+  }
+
   // (fcmp uno x, c) | (fcmp uno y, c)  -> (fcmp uno x, y)
   if (FCmpInst *LHS = dyn_cast<FCmpInst>(I.getOperand(0)))
     if (FCmpInst *RHS = dyn_cast<FCmpInst>(I.getOperand(1)))