[InstCombine] LogicOpc (zext X), C --> zext (LogicOpc X, C) (PR28476)

The benefits of this change include:
1. Remove DeMorgan-matching code that was added specifically to work-around 
   the missing transform in http://reviews.llvm.org/rL248634.
2. Makes the DeMorgan transform work for vectors too.
3. Fix PR28476: https://llvm.org/bugs/show_bug.cgi?id=28476

Extending this transform to other casts and other associative operators may
be useful too. See https://reviews.llvm.org/D22421 for a prerequisite for
doing that though.

Differential Revision: https://reviews.llvm.org/D22271

llvm-svn: 276221

2 files changed, 16 insertions, 28 deletions

diff --git a/llvm/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp b/llvm/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp
index 4314b2b0a37..3871b8ab636 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp
@@ -1123,26 +1123,6 @@ static Instruction *matchDeMorgansLaws(BinaryOperator &I,
         return BinaryOperator::CreateNot(LogicOp);
       }
 
-  // De Morgan's Law in disguise:
-  // (zext(bool A) ^ 1) & (zext(bool B) ^ 1) -> zext(~(A | B))
-  // (zext(bool A) ^ 1) | (zext(bool B) ^ 1) -> zext(~(A & B))
-  Value *A = nullptr;
-  Value *B = nullptr;
-  ConstantInt *C1 = nullptr;
-  if (match(Op0, m_OneUse(m_Xor(m_ZExt(m_Value(A)), m_ConstantInt(C1)))) &&
-      match(Op1, m_OneUse(m_Xor(m_ZExt(m_Value(B)), m_Specific(C1))))) {
-    // TODO: This check could be loosened to handle different type sizes.
-    // Alternatively, we could fix the definition of m_Not to recognize a not
-    // operation hidden by a zext?
-    if (A->getType()->isIntegerTy(1) && B->getType()->isIntegerTy(1) &&
-        C1->isOne()) {
-      Value *LogicOp = Builder->CreateBinOp(Opcode, A, B,
-                                            I.getName() + ".demorgan");
-      Value *Not = Builder->CreateNot(LogicOp);
-      return CastInst::CreateZExtOrBitCast(Not, I.getType());
-    }
-  }
-
   return nullptr;
 }
 
@@ -1199,6 +1179,22 @@ Instruction *InstCombiner::foldCastedBitwiseLogic(BinaryOperator &I) {
     return CastInst::CreateBitOrPointerCast(NewOp, DestTy);
   }
 
+  // Similarly, if one operand is zexted and the other is a constant, move the
+  // logic operation ahead of the zext if the constant is unchanged in the
+  // smaller source type. Performing the logic in a smaller type may provide
+  // more information to later folds, and the smaller logic instruction may be
+  // cheaper (particularly in the case of vectors).
+  Value *X;
+  if (match(Op0, m_OneUse(m_ZExt(m_Value(X)))) && match(Op1, m_Constant(C))) {
+    Constant *TruncC = ConstantExpr::getTrunc(C, SrcTy);
+    Constant *ZextTruncC = ConstantExpr::getZExt(TruncC, DestTy);
+    if (ZextTruncC == C) {
+      // LogicOpc (zext X), C --> zext (LogicOpc X, C)
+      Value *NewOp = Builder->CreateBinOp(LogicOpc, X, TruncC);
+      return new ZExtInst(NewOp, DestTy);
+    }
+  }
+
   CastInst *Cast1 = dyn_cast<CastInst>(Op1);
   if (!Cast1)
     return nullptr;
diff --git a/llvm/lib/Transforms/InstCombine/InstCombineCasts.cpp b/llvm/lib/Transforms/InstCombine/InstCombineCasts.cpp
index 8f3b8badcdf..0d79733aae9 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineCasts.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineCasts.cpp
@@ -920,14 +920,6 @@ Instruction *InstCombiner::visitZExt(ZExtInst &CI) {
     return BinaryOperator::CreateXor(Builder->CreateAnd(X, ZC), ZC);
   }
 
-  // zext (xor i1 X, true) to i32  --> xor (zext i1 X to i32), 1
-  if (SrcI && SrcI->hasOneUse() &&
-      SrcI->getType()->getScalarType()->isIntegerTy(1) &&
-      match(SrcI, m_Not(m_Value(X))) && (!X->hasOneUse() || !isa<CmpInst>(X))) {
-    Value *New = Builder->CreateZExt(X, CI.getType());
-    return BinaryOperator::CreateXor(New, ConstantInt::get(CI.getType(), 1));
-  }
-
   return nullptr;
 }