Exploit distributive laws (eg: And distributes over Or, Mul over Add, etc) in a

fairly systematic way in instcombine.  Some of these cases were already dealt
with, in which case I removed the existing code.  The case of Add has a bunch of
funky logic which covers some of this plus a few variants (considers shifts to be
a form of multiplication), which I didn't touch.  The simplification performed is:
A*B+A*C -> A*(B+C).  The improvement is to do this in cases that were not already
handled [such as A*B-A*C -> A*(B-C), which was reported on the mailing list], and
also to do it more often by not checking for "only one use" if "B+C" simplifies.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@120024 91177308-0d34-0410-b5e6-96231b3b80d8

lib/Transforms/InstCombine/InstCombine.h

@@ -290,6 +290,12 @@ private:
   /// operators which are associative or commutative.
   bool SimplifyAssociativeOrCommutative(BinaryOperator &I);
 
+  /// SimplifyDistributed - This tries to simplify binary operations which some
+  /// other binary operation distributes over (eg "A*B+A*C" -> "A*(B+C)" since
+  /// addition is distributed over by multiplication).  Returns the result of
+  /// the simplification, or null if no simplification was performed.
+  Instruction *SimplifyDistributed(BinaryOperator &I);
+
   /// SimplifyDemandedUseBits - Attempts to replace V with a simpler value
   /// based on the demanded bits.
   Value *SimplifyDemandedUseBits(Value *V, APInt DemandedMask, 

lib/Transforms/InstCombine/InstCombineAddSub.cpp

@@ -91,6 +91,8 @@ Instruction *InstCombiner::visitAdd(BinaryOperator &I) {
                                  I.hasNoUnsignedWrap(), TD))
     return ReplaceInstUsesWith(I, V);
 
+  if (Instruction *NV = SimplifyDistributed(I)) // (A*B)+(A*C) -> A*(B+C)
+    return NV;
   
   if (Constant *RHSC = dyn_cast<Constant>(RHS)) {
     if (ConstantInt *CI = dyn_cast<ConstantInt>(RHSC)) {
@@ -548,6 +550,9 @@ Instruction *InstCombiner::visitSub(BinaryOperator &I) {
   if (Op0 == Op1)                        // sub X, X  -> 0
     return ReplaceInstUsesWith(I, Constant::getNullValue(I.getType()));
 
+  if (Instruction *NV = SimplifyDistributed(I)) // (A*B)-(A*C) -> A*(B-C)
+    return NV;
+  
   // If this is a 'B = x-(-A)', change to B = x+A.  This preserves NSW/NUW.
   if (Value *V = dyn_castNegVal(Op1)) {
     BinaryOperator *Res = BinaryOperator::CreateAdd(Op0, V);

lib/Transforms/InstCombine/InstCombineAndOrXor.cpp

@@ -984,6 +984,9 @@ Instruction *InstCombiner::visitAnd(BinaryOperator &I) {
   if (Value *V = SimplifyAndInst(Op0, Op1, TD))
     return ReplaceInstUsesWith(I, V);
 
+  if (Instruction *NV = SimplifyDistributed(I)) // (A|B)&(A|C) -> A|(B&C)
+    return NV;
+
   // See if we can simplify any instructions used by the instruction whose sole 
   // purpose is to compute bits we don't care about.
   if (SimplifyDemandedInstructionBits(I))
@@ -1692,6 +1695,9 @@ Instruction *InstCombiner::visitOr(BinaryOperator &I) {
   if (Value *V = SimplifyOrInst(Op0, Op1, TD))
     return ReplaceInstUsesWith(I, V);
 
+  if (Instruction *NV = SimplifyDistributed(I)) // (A&B)|(A&C) -> A&(B|C)
+    return NV;
+
   // See if we can simplify any instructions used by the instruction whose sole 
   // purpose is to compute bits we don't care about.
   if (SimplifyDemandedInstructionBits(I))
@@ -1766,7 +1772,7 @@ Instruction *InstCombiner::visitOr(BinaryOperator &I) {
   Value *C = 0, *D = 0;
   if (match(Op0, m_And(m_Value(A), m_Value(C))) &&
       match(Op1, m_And(m_Value(B), m_Value(D)))) {
-    Value *V1 = 0, *V2 = 0, *V3 = 0;
+    Value *V1 = 0, *V2 = 0;
     C1 = dyn_cast<ConstantInt>(C);
     C2 = dyn_cast<ConstantInt>(D);
     if (C1 && C2) {  // (A & C1)|(B & C2)
@@ -1824,25 +1830,6 @@ Instruction *InstCombiner::visitOr(BinaryOperator &I) {
         }
       }
     }
-    
-    // Check to see if we have any common things being and'ed.  If so, find the
-    // terms for V1 & (V2|V3).
-    if (Op0->hasOneUse() || Op1->hasOneUse()) {
-      V1 = 0;
-      if (A == B)      // (A & C)|(A & D) == A & (C|D)
-        V1 = A, V2 = C, V3 = D;
-      else if (A == D) // (A & C)|(B & A) == A & (B|C)
-        V1 = A, V2 = B, V3 = C;
-      else if (C == B) // (A & C)|(C & D) == C & (A|D)
-        V1 = C, V2 = A, V3 = D;
-      else if (C == D) // (A & C)|(B & C) == C & (A|B)
-        V1 = C, V2 = A, V3 = B;
-      
-      if (V1) {
-        Value *Or = Builder->CreateOr(V2, V3, "tmp");
-        return BinaryOperator::CreateAnd(V1, Or);
-      }
-    }
 
     // (A & (C0?-1:0)) | (B & ~(C0?-1:0)) ->  C0 ? A : B, and commuted variants.
     // Don't do this for vector select idioms, the code generator doesn't handle
@@ -1979,6 +1966,9 @@ Instruction *InstCombiner::visitXor(BinaryOperator &I) {
   if (Value *V = SimplifyXorInst(Op0, Op1, TD))
     return ReplaceInstUsesWith(I, V);
 
+  if (Instruction *NV = SimplifyDistributed(I)) // (A&B)^(A&C) -> A&(B^C)
+    return NV;
+
   // See if we can simplify any instructions used by the instruction whose sole 
   // purpose is to compute bits we don't care about.
   if (SimplifyDemandedInstructionBits(I))
@@ -2172,29 +2162,8 @@ Instruction *InstCombiner::visitXor(BinaryOperator &I) {
       if ((A == C && B == D) || (A == D && B == C)) 
         return BinaryOperator::CreateXor(A, B);
     }
-    
-    // (A & B)^(C & D)
-    if ((Op0I->hasOneUse() || Op1I->hasOneUse()) &&
-        match(Op0I, m_And(m_Value(A), m_Value(B))) &&
-        match(Op1I, m_And(m_Value(C), m_Value(D)))) {
-      // (X & Y)^(X & Y) -> (Y^Z) & X
-      Value *X = 0, *Y = 0, *Z = 0;
-      if (A == C)
-        X = A, Y = B, Z = D;
-      else if (A == D)
-        X = A, Y = B, Z = C;
-      else if (B == C)
-        X = B, Y = A, Z = D;
-      else if (B == D)
-        X = B, Y = A, Z = C;
-      
-      if (X) {
-        Value *NewOp = Builder->CreateXor(Y, Z, Op0->getName());
-        return BinaryOperator::CreateAnd(NewOp, X);
-      }
-    }
   }
-    
+
   // (icmp1 A, B) ^ (icmp2 A, B) --> (icmp3 A, B)
   if (ICmpInst *RHS = dyn_cast<ICmpInst>(I.getOperand(1)))
     if (ICmpInst *LHS = dyn_cast<ICmpInst>(I.getOperand(0)))

lib/Transforms/InstCombine/InstructionCombining.cpp

@@ -237,6 +237,117 @@ bool InstCombiner::SimplifyAssociativeOrCommutative(BinaryOperator &I) {
   } while (1);
 }
 
+/// LeftDistributesOverRight - Whether "X LOp (Y ROp Z)" is always equal to
+/// "(X LOp Y) ROp (Z LOp Z)".
+static bool LeftDistributesOverRight(Instruction::BinaryOps LOp,
+                                     Instruction::BinaryOps ROp) {
+  switch (LOp) {
+  default:
+    return false;
+
+  case Instruction::And:
+    // And distributes over Or and Xor.
+    switch (ROp) {
+    default:
+      return false;
+    case Instruction::Or:
+    case Instruction::Xor:
+      return true;
+    }
+
+  case Instruction::Mul:
+    // Multiplication distributes over addition and subtraction.
+    switch (ROp) {
+    default:
+      return false;
+    case Instruction::Add:
+    case Instruction::Sub:
+      return true;
+    }
+
+  case Instruction::Or:
+    // Or distributes over And.
+    switch (ROp) {
+    default:
+      return false;
+    case Instruction::And:
+      return true;
+    }
+  }
+}
+
+/// RightDistributesOverLeft - Whether "(X LOp Y) ROp Z" is always equal to
+/// "(X ROp Z) LOp (Y ROp Z)".
+static bool RightDistributesOverLeft(Instruction::BinaryOps LOp,
+                                     Instruction::BinaryOps ROp) {
+  if (Instruction::isCommutative(ROp))
+    return LeftDistributesOverRight(ROp, LOp);
+  // TODO: It would be nice to handle division, aka "(X + Y)/Z = X/Z + Y/Z",
+  // but this requires knowing that the addition does not overflow and other
+  // such subtleties.
+  return false;
+}
+
+/// SimplifyDistributed - This tries to simplify binary operations which some
+/// other binary operation distributes over (eg "A*B+A*C" -> "A*(B+C)" since
+/// addition is distributed over by multiplication).  Returns the result of
+/// the simplification, or null if no simplification was performed.
+Instruction *InstCombiner::SimplifyDistributed(BinaryOperator &I) {
+  BinaryOperator *Op0 = dyn_cast<BinaryOperator>(I.getOperand(0));
+  BinaryOperator *Op1 = dyn_cast<BinaryOperator>(I.getOperand(1));
+  if (!Op0 || !Op1 || Op0->getOpcode() != Op1->getOpcode())
+    return 0;
+
+  // The instruction has the form "(A op' B) op (C op' D)".
+  Value *A = Op0->getOperand(0); Value *B = Op0->getOperand(1);
+  Value *C = Op1->getOperand(0); Value *D = Op1->getOperand(1);
+  Instruction::BinaryOps OuterOpcode = I.getOpcode(); // op
+  Instruction::BinaryOps InnerOpcode = Op0->getOpcode(); // op'
+
+  // Does "X op' (Y op Z)" always equal "(X op' Y) op (X op' Z)"?
+  bool LeftDistributes = LeftDistributesOverRight(InnerOpcode, OuterOpcode);
+  // Does "(X op Y) op' Z" always equal "(X op' Z) op (Y op' Z)"?
+  bool RightDistributes = RightDistributesOverLeft(OuterOpcode, InnerOpcode);
+  // Does "X op' Y" always equal "Y op' X"?
+  bool InnerCommutative = Instruction::isCommutative(InnerOpcode);
+
+  if (LeftDistributes)
+    // Does the instruction have the form "(A op' B) op (A op' D)" or, in the
+    // commutative case, "(A op' B) op (C op' A)"?
+    if (A == C || (InnerCommutative && A == D)) {
+      if (A != C)
+        std::swap(C, D);
+      // Consider forming "A op' (B op D)".
+      // If "B op D" simplifies then it can be formed with no cost.
+      Value *RHS = SimplifyBinOp(OuterOpcode, B, D, TD);
+      // If "B op D" doesn't simplify then only proceed if both of the existing
+      // operations "A op' B" and "C op' D" will be zapped since no longer used.
+      if (!RHS && Op0->hasOneUse() && Op1->hasOneUse())
+        RHS = Builder->CreateBinOp(OuterOpcode, B, D, Op1->getName());
+      if (RHS)
+        return BinaryOperator::Create(InnerOpcode, A, RHS);
+    }
+
+  if (RightDistributes)
+    // Does the instruction have the form "(A op' B) op (C op' B)" or, in the
+    // commutative case, "(A op' B) op (B op' D)"?
+    if (B == D || (InnerCommutative && B == C)) {
+      if (B != D)
+        std::swap(C, D);
+      // Consider forming "(A op C) op' B".
+      // If "A op C" simplifies then it can be formed with no cost.
+      Value *LHS = SimplifyBinOp(OuterOpcode, A, C, TD);
+      // If "A op C" doesn't simplify then only proceed if both of the existing
+      // operations "A op' B" and "C op' D" will be zapped since no longer used.
+      if (!LHS && Op0->hasOneUse() && Op1->hasOneUse())
+        LHS = Builder->CreateBinOp(OuterOpcode, A, C, Op0->getName());
+      if (LHS)
+        return BinaryOperator::Create(InnerOpcode, LHS, B);
+    }
+
+  return 0;
+}
+
 // dyn_castNegVal - Given a 'sub' instruction, return the RHS of the instruction
 // if the LHS is a constant zero (which is the 'negate' form).
 //

test/Transforms/InstCombine/2010-11-23-Distributed.ll

@@ -0,0 +1,11 @@
+; RUN: opt < %s -instcombine -S | FileCheck %s
+define i32 @foo(i32 %x, i32 %y) {
+; CHECK: @foo
+  %add = add nsw i32 %y, %x
+  %mul = mul nsw i32 %add, %y
+  %square = mul nsw i32 %y, %y
+  %res = sub i32 %mul, %square
+; CHECK: %res = mul i32 %x, %y
+  ret i32 %res
+; CHECK: ret i32 %res
+}