[llvm] r194525 - Fold (iszero(A&K1) | iszero(A&K2)) -> (A&(K1|K2)) != (K1|K2) if we know that K1 and K2 are 'one-hot' (only one bit is on).

[Nadav Rotem]

Author: nadav
Date: Tue Nov 12 16:38:59 2013
New Revision: 194525

URL: http://llvm.org/viewvc/llvm-project?rev=194525&view=rev
Log:
Fold (iszero(A&K1) | iszero(A&K2)) ->  (A&(K1|K2)) != (K1|K2) if we know that K1 and K2 are 'one-hot' (only one bit is on).


Added:
    llvm/trunk/test/Transforms/InstCombine/onehot_merge.ll
Modified:
    llvm/trunk/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp

Modified: llvm/trunk/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp?rev=194525&r1=194524&r2=194525&view=diff
==============================================================================
--- llvm/trunk/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp (original)
+++ llvm/trunk/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp Tue Nov 12 16:38:59 2013
@@ -1543,10 +1543,60 @@ static Instruction *MatchSelectFromAndOr
   return 0;
 }
 
+/// IsSingleBitValue - Returns true for "one-hot" values (values where at most
+/// one bit can be set).
+static bool IsOneHotValue(Value *V) {
+  // Match 1<<K.
+  if (BinaryOperator *BO = dyn_cast<BinaryOperator>(V))
+    if (BO->getOpcode() == Instruction::Shl) {
+      ConstantInt *One = dyn_cast<ConstantInt>(BO->getOperand(0));
+      return One && One->isOne();
+    }
+
+  // Check for power of two integer constants.
+  if (ConstantInt *K = dyn_cast<ConstantInt>(V))
+    return K->getValue().isPowerOf2();
+
+  return false;
+}
+
 /// FoldOrOfICmps - Fold (icmp)|(icmp) if possible.
 Value *InstCombiner::FoldOrOfICmps(ICmpInst *LHS, ICmpInst *RHS) {
   ICmpInst::Predicate LHSCC = LHS->getPredicate(), RHSCC = RHS->getPredicate();
 
+  // Fold (iszero(A & K1) | iszero(A & K2)) ->  (A & (K1 | K2)) != (K1 | K2)
+  // if K1 and K2 are a one-bit mask.
+  ConstantInt *LHSCst = dyn_cast<ConstantInt>(LHS->getOperand(1));
+  ConstantInt *RHSCst = dyn_cast<ConstantInt>(RHS->getOperand(1));
+
+  if (LHS->getPredicate() == ICmpInst::ICMP_EQ && LHSCst && LHSCst->isZero() &&
+      RHS->getPredicate() == ICmpInst::ICMP_EQ && RHSCst && RHSCst->isZero()) {
+
+    BinaryOperator *LAnd = dyn_cast<BinaryOperator>(LHS->getOperand(0));
+    BinaryOperator *RAnd = dyn_cast<BinaryOperator>(RHS->getOperand(0));
+    if (LAnd && RAnd && LAnd->hasOneUse() && RHS->hasOneUse() &&
+        LAnd->getOpcode() == Instruction::And &&
+        RAnd->getOpcode() == Instruction::And) {
+
+      Value *Mask = 0;
+      Value *Masked = 0;
+      if (LAnd->getOperand(0) == RAnd->getOperand(0) &&
+          IsOneHotValue(LAnd->getOperand(1)) &&
+          IsOneHotValue(RAnd->getOperand(1))) {
+        Mask = Builder->CreateOr(LAnd->getOperand(1), RAnd->getOperand(1));
+        Masked = Builder->CreateAnd(LAnd->getOperand(0), Mask);
+      } else if (LAnd->getOperand(1) == RAnd->getOperand(1) &&
+                 IsOneHotValue(LAnd->getOperand(0)) &&
+                 IsOneHotValue(RAnd->getOperand(0))) {
+        Mask = Builder->CreateOr(LAnd->getOperand(0), RAnd->getOperand(0));
+        Masked = Builder->CreateAnd(LAnd->getOperand(1), Mask);
+      }
+
+      if (Masked)
+        return Builder->CreateICmp(ICmpInst::ICMP_NE, Masked, Mask);
+    }
+  }
+
   // (icmp1 A, B) | (icmp2 A, B) --> (icmp3 A, B)
   if (PredicatesFoldable(LHSCC, RHSCC)) {
     if (LHS->getOperand(0) == RHS->getOperand(1) &&
@@ -1567,9 +1617,6 @@ Value *InstCombiner::FoldOrOfICmps(ICmpI
     return V;
 
   Value *Val = LHS->getOperand(0), *Val2 = RHS->getOperand(0);
-  ConstantInt *LHSCst = dyn_cast<ConstantInt>(LHS->getOperand(1));
-  ConstantInt *RHSCst = dyn_cast<ConstantInt>(RHS->getOperand(1));
-
   if (LHS->hasOneUse() || RHS->hasOneUse()) {
     // (icmp eq B, 0) | (icmp ult A, B) -> (icmp ule A, B-1)
     // (icmp eq B, 0) | (icmp ugt B, A) -> (icmp ule A, B-1)

Added: llvm/trunk/test/Transforms/InstCombine/onehot_merge.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/InstCombine/onehot_merge.ll?rev=194525&view=auto
==============================================================================
--- llvm/trunk/test/Transforms/InstCombine/onehot_merge.ll (added)
+++ llvm/trunk/test/Transforms/InstCombine/onehot_merge.ll Tue Nov 12 16:38:59 2013
@@ -0,0 +1,35 @@
+; RUN: opt < %s -instcombine -S | FileCheck %s
+
+;CHECK: @and_consts
+;CHECK: and i32 %k, 12
+;CHECK: icmp ne i32 %0, 12
+;CHECK: ret
+define i1 @and_consts(i32 %k, i32 %c1, i32 %c2) {
+bb:
+  %tmp1 = and i32 4, %k
+  %tmp2 = icmp eq i32 %tmp1, 0
+  %tmp5 = and i32 8, %k
+  %tmp6 = icmp eq i32 %tmp5, 0
+  %or = or i1 %tmp2, %tmp6
+  ret i1 %or
+}
+
+;CHECK: @foo1_and
+;CHECK:  shl i32 1, %c1
+;CHECK-NEXT:  shl i32 1, %c2
+;CHECK-NEXT:  or i32
+;CHECK-NEXT:  and i32
+;CHECK-NEXT:  icmp ne i32 %1, %0
+;CHECK: ret
+define i1 @foo1_and(i32 %k, i32 %c1, i32 %c2) {
+bb:
+  %tmp = shl i32 1, %c1
+  %tmp4 = shl i32 1, %c2
+  %tmp1 = and i32 %tmp, %k
+  %tmp2 = icmp eq i32 %tmp1, 0
+  %tmp5 = and i32 %tmp4, %k
+  %tmp6 = icmp eq i32 %tmp5, 0
+  %or = or i1 %tmp2, %tmp6
+  ret i1 %or
+}
+