Generalize the reassociation transform in SimplifyCommutative (now renamed to

SimplifyAssociativeOrCommutative) "(A op C1) op C2" -> "A op (C1 op C2)",
which previously was only done if C1 and C2 were constants, to occur whenever
"C1 op C2" simplifies (a la InstructionSimplify).  Since the simplifying operand
combination can no longer be assumed to be the right-hand terms, consider all of
the possible permutations.  When compiling "gcc as one big file", transform 2
(i.e. using right-hand operands) fires about 4000 times but it has to be said
that most of the time the simplifying operands are both constants.  Transforms
3, 4 and 5 each fired once.  Transform 6, which is an existing transform that
I didn't change, never fired.  With this change, the testcase is now optimized
perfectly with one run of instcombine (previously it required instcombine +
reassociate + instcombine, and it may just have been luck that this worked).

llvm-svn: 119002

5 files changed, 128 insertions, 46 deletions

diff --git a/llvm/lib/Transforms/InstCombine/InstCombine.h b/llvm/lib/Transforms/InstCombine/InstCombine.h
index 3b8cbe2a1e4..05846d0f9e1 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombine.h
+++ b/llvm/lib/Transforms/InstCombine/InstCombine.h
@@ -286,9 +286,9 @@ public:
 
 private:
 
-  /// SimplifyCommutative - This performs a few simplifications for 
-  /// commutative operators.
-  bool SimplifyCommutative(BinaryOperator &I);
+  /// SimplifyAssociativeOrCommutative - This performs a few simplifications for
+  /// operators which are associative or commutative.
+  bool SimplifyAssociativeOrCommutative(BinaryOperator &I);
 
   /// SimplifyDemandedUseBits - Attempts to replace V with a simpler value
   /// based on the demanded bits.
diff --git a/llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp b/llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp
index 4d2c89e60f0..9b72eb924ac 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp
@@ -84,7 +84,7 @@ bool InstCombiner::WillNotOverflowSignedAdd(Value *LHS, Value *RHS) {
 }
 
 Instruction *InstCombiner::visitAdd(BinaryOperator &I) {
-  bool Changed = SimplifyCommutative(I);
+  bool Changed = SimplifyAssociativeOrCommutative(I);
   Value *LHS = I.getOperand(0), *RHS = I.getOperand(1);
 
   if (Value *V = SimplifyAddInst(LHS, RHS, I.hasNoSignedWrap(),
@@ -342,7 +342,7 @@ Instruction *InstCombiner::visitAdd(BinaryOperator &I) {
 }
 
 Instruction *InstCombiner::visitFAdd(BinaryOperator &I) {
-  bool Changed = SimplifyCommutative(I);
+  bool Changed = SimplifyAssociativeOrCommutative(I);
   Value *LHS = I.getOperand(0), *RHS = I.getOperand(1);
 
   if (Constant *RHSC = dyn_cast<Constant>(RHS)) {
diff --git a/llvm/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp b/llvm/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp
index 4f8240ac2ee..864b47758b2 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp
@@ -978,7 +978,7 @@ Value *InstCombiner::FoldAndOfFCmps(FCmpInst *LHS, FCmpInst *RHS) {
 
 
 Instruction *InstCombiner::visitAnd(BinaryOperator &I) {
-  bool Changed = SimplifyCommutative(I);
+  bool Changed = SimplifyAssociativeOrCommutative(I);
   Value *Op0 = I.getOperand(0), *Op1 = I.getOperand(1);
 
   if (Value *V = SimplifyAndInst(Op0, Op1, TD))
@@ -1686,7 +1686,7 @@ Instruction *InstCombiner::FoldOrWithConstants(BinaryOperator &I, Value *Op,
 }
 
 Instruction *InstCombiner::visitOr(BinaryOperator &I) {
-  bool Changed = SimplifyCommutative(I);
+  bool Changed = SimplifyAssociativeOrCommutative(I);
   Value *Op0 = I.getOperand(0), *Op1 = I.getOperand(1);
 
   if (Value *V = SimplifyOrInst(Op0, Op1, TD))
@@ -1973,7 +1973,7 @@ Instruction *InstCombiner::visitOr(BinaryOperator &I) {
 }
 
 Instruction *InstCombiner::visitXor(BinaryOperator &I) {
-  bool Changed = SimplifyCommutative(I);
+  bool Changed = SimplifyAssociativeOrCommutative(I);
   Value *Op0 = I.getOperand(0), *Op1 = I.getOperand(1);
 
   if (isa<UndefValue>(Op1)) {
diff --git a/llvm/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp b/llvm/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp
index b3974e8eeff..c2ae4cc6371 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp
@@ -47,7 +47,7 @@ static bool MultiplyOverflows(ConstantInt *C1, ConstantInt *C2, bool sign) {
 }
 
 Instruction *InstCombiner::visitMul(BinaryOperator &I) {
-  bool Changed = SimplifyCommutative(I);
+  bool Changed = SimplifyAssociativeOrCommutative(I);
   Value *Op0 = I.getOperand(0), *Op1 = I.getOperand(1);
 
   if (isa<UndefValue>(Op1))              // undef * X -> 0
@@ -194,7 +194,7 @@ Instruction *InstCombiner::visitMul(BinaryOperator &I) {
 }
 
 Instruction *InstCombiner::visitFMul(BinaryOperator &I) {
-  bool Changed = SimplifyCommutative(I);
+  bool Changed = SimplifyAssociativeOrCommutative(I);
   Value *Op0 = I.getOperand(0), *Op1 = I.getOperand(1);
 
   // Simplify mul instructions with a constant RHS...
diff --git a/llvm/lib/Transforms/InstCombine/InstructionCombining.cpp b/llvm/lib/Transforms/InstCombine/InstructionCombining.cpp
index de409d1ccee..61676f82b1e 100644
--- a/llvm/lib/Transforms/InstCombine/InstructionCombining.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstructionCombining.cpp
@@ -106,53 +106,135 @@ bool InstCombiner::ShouldChangeType(const Type *From, const Type *To) const {
 }
 
 
-// SimplifyCommutative - This performs a few simplifications for commutative
-// operators:
+/// SimplifyAssociativeOrCommutative - This performs a few simplifications for
+/// operators which are associative or commutative:
+//
+//  Commutative operators:
 //
 //  1. Order operands such that they are listed from right (least complex) to
 //     left (most complex).  This puts constants before unary operators before
 //     binary operators.
 //
-//  2. Transform: (op (op V, C1), C2) ==> (op V, (op C1, C2))
-//  3. Transform: (op (op V1, C1), (op V2, C2)) ==> (op (op V1, V2), (op C1,C2))
+//  Associative operators:
+//
+//  2. Transform: "(A op B) op C" ==> "A op (B op C)" if "B op C" simplifies.
+//  3. Transform: "A op (B op C)" ==> "(A op B) op C" if "A op B" simplifies.
+//
+//  Associative and commutative operators:
+//
+//  4. Transform: "(A op B) op C" ==> "(C op A) op B" if "C op A" simplifies.
+//  5. Transform: "A op (B op C)" ==> "B op (C op A)" if "C op A" simplifies.
+//  6. Transform: "(A op C1) op (B op C2)" ==> "(A op B) op (C1 op C2)"
+//     if C1 and C2 are constants.
 //
-bool InstCombiner::SimplifyCommutative(BinaryOperator &I) {
+bool InstCombiner::SimplifyAssociativeOrCommutative(BinaryOperator &I) {
+  Instruction::BinaryOps Opcode = I.getOpcode();
   bool Changed = false;
-  if (getComplexity(I.getOperand(0)) < getComplexity(I.getOperand(1)))
-    Changed = !I.swapOperands();
 
-  if (!I.isAssociative()) return Changed;
-  
-  Instruction::BinaryOps Opcode = I.getOpcode();
-  if (BinaryOperator *Op = dyn_cast<BinaryOperator>(I.getOperand(0)))
-    if (Op->getOpcode() == Opcode && isa<Constant>(Op->getOperand(1))) {
-      if (isa<Constant>(I.getOperand(1))) {
-        Constant *Folded = ConstantExpr::get(I.getOpcode(),
-                                             cast<Constant>(I.getOperand(1)),
-                                             cast<Constant>(Op->getOperand(1)));
-        I.setOperand(0, Op->getOperand(0));
-        I.setOperand(1, Folded);
-        return true;
+  do {
+    // Order operands such that they are listed from right (least complex) to
+    // left (most complex).  This puts constants before unary operators before
+    // binary operators.
+    if (I.isCommutative() && getComplexity(I.getOperand(0)) <
+        getComplexity(I.getOperand(1)))
+      Changed = !I.swapOperands();
+
+    BinaryOperator *Op0 = dyn_cast<BinaryOperator>(I.getOperand(0));
+    BinaryOperator *Op1 = dyn_cast<BinaryOperator>(I.getOperand(1));
+
+    if (I.isAssociative()) {
+      // Transform: "(A op B) op C" ==> "A op (B op C)" if "B op C" simplifies.
+      if (Op0 && Op0->getOpcode() == Opcode) {
+        Value *A = Op0->getOperand(0);
+        Value *B = Op0->getOperand(1);
+        Value *C = I.getOperand(1);
+
+        // Does "B op C" simplify?
+        if (Value *V = SimplifyBinOp(Opcode, B, C, TD)) {
+          // It simplifies to V.  Form "A op V".
+          I.setOperand(0, A);
+          I.setOperand(1, V);
+          Changed = true;
+          continue;
+        }
       }
-      
-      if (BinaryOperator *Op1 = dyn_cast<BinaryOperator>(I.getOperand(1)))
-        if (Op1->getOpcode() == Opcode && isa<Constant>(Op1->getOperand(1)) &&
-            Op->hasOneUse() && Op1->hasOneUse()) {
-          Constant *C1 = cast<Constant>(Op->getOperand(1));
-          Constant *C2 = cast<Constant>(Op1->getOperand(1));
-
-          // Fold (op (op V1, C1), (op V2, C2)) ==> (op (op V1, V2), (op C1,C2))
-          Constant *Folded = ConstantExpr::get(I.getOpcode(), C1, C2);
-          Instruction *New = BinaryOperator::Create(Opcode, Op->getOperand(0),
-                                                    Op1->getOperand(0),
-                                                    Op1->getName(), &I);
-          Worklist.Add(New);
-          I.setOperand(0, New);
-          I.setOperand(1, Folded);
-          return true;
+
+      // Transform: "A op (B op C)" ==> "(A op B) op C" if "A op B" simplifies.
+      if (Op1 && Op1->getOpcode() == Opcode) {
+        Value *A = I.getOperand(0);
+        Value *B = Op1->getOperand(0);
+        Value *C = Op1->getOperand(1);
+
+        // Does "A op B" simplify?
+        if (Value *V = SimplifyBinOp(Opcode, A, B, TD)) {
+          // It simplifies to V.  Form "V op C".
+          I.setOperand(0, V);
+          I.setOperand(1, C);
+          Changed = true;
+          continue;
         }
+      }
     }
-  return Changed;
+
+    if (I.isAssociative() && I.isCommutative()) {
+      // Transform: "(A op B) op C" ==> "(C op A) op B" if "C op A" simplifies.
+      if (Op0 && Op0->getOpcode() == Opcode) {
+        Value *A = Op0->getOperand(0);
+        Value *B = Op0->getOperand(1);
+        Value *C = I.getOperand(1);
+
+        // Does "C op A" simplify?
+        if (Value *V = SimplifyBinOp(Opcode, C, A, TD)) {
+          // It simplifies to V.  Form "V op B".
+          I.setOperand(0, V);
+          I.setOperand(1, B);
+          Changed = true;
+          continue;
+        }
+      }
+
+      // Transform: "A op (B op C)" ==> "B op (C op A)" if "C op A" simplifies.
+      if (Op1 && Op1->getOpcode() == Opcode) {
+        Value *A = I.getOperand(0);
+        Value *B = Op1->getOperand(0);
+        Value *C = Op1->getOperand(1);
+
+        // Does "C op A" simplify?
+        if (Value *V = SimplifyBinOp(Opcode, C, A, TD)) {
+          // It simplifies to V.  Form "B op V".
+          I.setOperand(0, B);
+          I.setOperand(1, V);
+          Changed = true;
+          continue;
+        }
+      }
+
+      // Transform: "(A op C1) op (B op C2)" ==> "(A op B) op (C1 op C2)"
+      // if C1 and C2 are constants.
+      if (Op0 && Op1 &&
+          Op0->getOpcode() == Opcode && Op1->getOpcode() == Opcode &&
+          isa<Constant>(Op0->getOperand(1)) &&
+          isa<Constant>(Op1->getOperand(1)) &&
+          Op0->hasOneUse() && Op1->hasOneUse()) {
+        Value *A = Op0->getOperand(0);
+        Constant *C1 = cast<Constant>(Op0->getOperand(1));
+        Value *B = Op1->getOperand(0);
+        Constant *C2 = cast<Constant>(Op1->getOperand(1));
+
+        Constant *Folded = ConstantExpr::get(Opcode, C1, C2);
+        Instruction *New = BinaryOperator::Create(Opcode, A, B, Op1->getName(),
+                                                  &I);
+        Worklist.Add(New);
+        I.setOperand(0, New);
+        I.setOperand(1, Folded);
+        Changed = true;
+        continue;
+      }
+    }
+
+    // No further simplifications.
+    return Changed;
+  } while (1);
 }
 
 // dyn_castNegVal - Given a 'sub' instruction, return the RHS of the instruction