[InstCombine] simplify getBinOpsForFactorization(); NFC

llvm-svn: 330129

1 files changed, 15 insertions, 25 deletions

diff --git a/llvm/lib/Transforms/InstCombine/InstructionCombining.cpp b/llvm/lib/Transforms/InstCombine/InstructionCombining.cpp
index af4449a9dd2..d33fba852e7 100644
--- a/llvm/lib/Transforms/InstCombine/InstructionCombining.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstructionCombining.cpp
@@ -486,37 +486,27 @@ static Value *getIdentityValue(Instruction::BinaryOps Opcode, Value *V) {
   return ConstantExpr::getBinOpIdentity(Opcode, V->getType());
 }
 
-/// This function factors binary ops which can be combined using distributive
-/// laws. This function tries to transform 'Op' based TopLevelOpcode to enable
-/// factorization e.g for ADD(SHL(X , 2), MUL(X, 5)), When this function called
-/// with TopLevelOpcode == Instruction::Add and Op = SHL(X, 2), transforms
-/// SHL(X, 2) to MUL(X, 4) i.e. returns Instruction::Mul with LHS set to 'X' and
-/// RHS to 4.
+/// This function predicates factorization using distributive laws. By default,
+/// it just returns the 'Op' inputs. But for special-cases like
+/// 'add(shl(X, 5), ...)', this function will have TopOpcode == Instruction::Add
+/// and Op = shl(X, 5). The 'shl' is treated as the more general 'mul X, 32' to
+/// allow more factorization opportunities.
 static Instruction::BinaryOps
-getBinOpsForFactorization(Instruction::BinaryOps TopLevelOpcode,
-                          BinaryOperator *Op, Value *&LHS, Value *&RHS) {
+getBinOpsForFactorization(Instruction::BinaryOps TopOpcode, BinaryOperator *Op,
+                          Value *&LHS, Value *&RHS) {
   assert(Op && "Expected a binary operator");
-
   LHS = Op->getOperand(0);
   RHS = Op->getOperand(1);
-
-  switch (TopLevelOpcode) {
-  default:
-    return Op->getOpcode();
-
-  case Instruction::Add:
-  case Instruction::Sub:
-    if (Op->getOpcode() == Instruction::Shl) {
-      if (Constant *CST = dyn_cast<Constant>(Op->getOperand(1))) {
-        // The multiplier is really 1 << CST.
-        RHS = ConstantExpr::getShl(ConstantInt::get(Op->getType(), 1), CST);
-        return Instruction::Mul;
-      }
+  if (TopOpcode == Instruction::Add || TopOpcode == Instruction::Sub) {
+    Constant *C;
+    if (match(Op, m_Shl(m_Value(), m_Constant(C)))) {
+      // X << C --> X * (1 << C)
+      RHS = ConstantExpr::getShl(ConstantInt::get(Op->getType(), 1), C);
+      return Instruction::Mul;
     }
-    return Op->getOpcode();
+    // TODO: We can add other conversions e.g. shr => div etc.
   }
-
-  // TODO: We can add other conversions e.g. shr => div etc.
+  return Op->getOpcode();
 }
 
 /// This tries to simplify binary operations by factorizing out common terms