According to my auto-simplifier the most common missed simplifications in

optimized code are:
  (non-negative number)+(power-of-two) != 0 -> true
and
  (x | 1) != 0 -> true
Instcombine knows about the second one of course, but only does it if X|1
has only one use.  These fire thousands of times in the testsuite.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@124183 91177308-0d34-0410-b5e6-96231b3b80d8

include/llvm/Analysis/ValueTracking.h

@@ -39,6 +39,23 @@ namespace llvm {
                          APInt &KnownOne, const TargetData *TD = 0,
                          unsigned Depth = 0);
   
+  /// ComputeSignBit - Determine whether the sign bit is known to be zero or
+  /// one.  Convenience wrapper around ComputeMaskedBits.
+  void ComputeSignBit(Value *V, bool &KnownZero, bool &KnownOne,
+                      const TargetData *TD = 0, unsigned Depth = 0);
+
+  /// isPowerOfTwo - Return true if the given value is known to have exactly one
+  /// bit set when defined. For vectors return true if every element is known to
+  /// be a power of two when defined.  Supports values with integer or pointer
+  /// type and vectors of integers.
+  bool isPowerOfTwo(Value *V, const TargetData *TD = 0, unsigned Depth = 0);
+
+  /// isKnownNonZero - Return true if the given value is known to be non-zero
+  /// when defined.  For vectors return true if every element is known to be
+  /// non-zero when defined.  Supports values with integer or pointer type and
+  /// vectors of integers.
+  bool isKnownNonZero(Value *V, const TargetData *TD = 0, unsigned Depth = 0);
+
   /// MaskedValueIsZero - Return true if 'V & Mask' is known to be zero.  We use
   /// this predicate to simplify operations downstream.  Mask is known to be
   /// zero for bits that V cannot have.

lib/Analysis/InstructionSimplify.cpp

@@ -22,6 +22,7 @@
 #include "llvm/Analysis/InstructionSimplify.h"
 #include "llvm/Analysis/ConstantFolding.h"
 #include "llvm/Analysis/Dominators.h"
+#include "llvm/Analysis/ValueTracking.h"
 #include "llvm/Support/PatternMatch.h"
 #include "llvm/Support/ValueHandle.h"
 #include "llvm/Target/TargetData.h"
@@ -1153,7 +1154,69 @@ static Value *SimplifyICmpInst(unsigned Predicate, Value *LHS, Value *RHS,
     }
   }
 
-  // See if we are doing a comparison with a constant.
+  // icmp <alloca*>, <global/alloca*/null> - Different stack variables have
+  // different addresses, and what's more the address of a stack variable is
+  // never null or equal to the address of a global.  Note that generalizing
+  // to the case where LHS is a global variable address or null is pointless,
+  // since if both LHS and RHS are constants then we already constant folded
+  // the compare, and if only one of them is then we moved it to RHS already.
+  if (isa<AllocaInst>(LHS) && (isa<GlobalValue>(RHS) || isa<AllocaInst>(RHS) ||
+                               isa<ConstantPointerNull>(RHS)))
+    // We already know that LHS != LHS.
+    return ConstantInt::get(ITy, CmpInst::isFalseWhenEqual(Pred));
+
+  // If we are comparing with zero then try hard since this is a common case.
+  if (match(RHS, m_Zero())) {
+    bool LHSKnownNonNegative, LHSKnownNegative;
+    switch (Pred) {
+    default:
+      assert(false && "Unknown ICmp predicate!");
+    case ICmpInst::ICMP_ULT:
+      return ConstantInt::getFalse(LHS->getContext());
+    case ICmpInst::ICMP_UGE:
+      return ConstantInt::getTrue(LHS->getContext());
+    case ICmpInst::ICMP_EQ:
+    case ICmpInst::ICMP_ULE:
+      if (isKnownNonZero(LHS, TD))
+        return ConstantInt::getFalse(LHS->getContext());
+      break;
+    case ICmpInst::ICMP_NE:
+    case ICmpInst::ICMP_UGT:
+      if (isKnownNonZero(LHS, TD))
+        return ConstantInt::getTrue(LHS->getContext());
+      break;
+    case ICmpInst::ICMP_SLT:
+      ComputeSignBit(LHS, LHSKnownNonNegative, LHSKnownNegative, TD);
+      if (LHSKnownNegative)
+        return ConstantInt::getTrue(LHS->getContext());
+      if (LHSKnownNonNegative)
+        return ConstantInt::getFalse(LHS->getContext());
+      break;
+    case ICmpInst::ICMP_SLE:
+      ComputeSignBit(LHS, LHSKnownNonNegative, LHSKnownNegative, TD);
+      if (LHSKnownNegative)
+        return ConstantInt::getTrue(LHS->getContext());
+      if (LHSKnownNonNegative && isKnownNonZero(LHS, TD))
+        return ConstantInt::getFalse(LHS->getContext());
+      break;
+    case ICmpInst::ICMP_SGE:
+      ComputeSignBit(LHS, LHSKnownNonNegative, LHSKnownNegative, TD);
+      if (LHSKnownNegative)
+        return ConstantInt::getFalse(LHS->getContext());
+      if (LHSKnownNonNegative)
+        return ConstantInt::getTrue(LHS->getContext());
+      break;
+    case ICmpInst::ICMP_SGT:
+      ComputeSignBit(LHS, LHSKnownNonNegative, LHSKnownNegative, TD);
+      if (LHSKnownNegative)
+        return ConstantInt::getFalse(LHS->getContext());
+      if (LHSKnownNonNegative && isKnownNonZero(LHS, TD))
+        return ConstantInt::getTrue(LHS->getContext());
+      break;
+    }
+  }
+
+  // See if we are doing a comparison with a constant integer.
   if (ConstantInt *CI = dyn_cast<ConstantInt>(RHS)) {
     switch (Pred) {
     default: break;
@@ -1192,17 +1255,6 @@ static Value *SimplifyICmpInst(unsigned Predicate, Value *LHS, Value *RHS,
     }
   }
 
-  // icmp <alloca*>, <global/alloca*/null> - Different stack variables have
-  // different addresses, and what's more the address of a stack variable is
-  // never null or equal to the address of a global.  Note that generalizing
-  // to the case where LHS is a global variable address or null is pointless,
-  // since if both LHS and RHS are constants then we already constant folded
-  // the compare, and if only one of them is then we moved it to RHS already.
-  if (isa<AllocaInst>(LHS) && (isa<GlobalValue>(RHS) || isa<AllocaInst>(RHS) ||
-                               isa<ConstantPointerNull>(RHS)))
-    // We already know that LHS != LHS.
-    return ConstantInt::get(ITy, CmpInst::isFalseWhenEqual(Pred));
-
   // Compare of cast, for example (zext X) != 0 -> X != 0
   if (isa<CastInst>(LHS) && (isa<Constant>(RHS) || isa<CastInst>(RHS))) {
     Instruction *LI = cast<CastInst>(LHS);

lib/Analysis/ValueTracking.cpp

@@ -24,9 +24,22 @@
 #include "llvm/Target/TargetData.h"
 #include "llvm/Support/GetElementPtrTypeIterator.h"
 #include "llvm/Support/MathExtras.h"
+#include "llvm/Support/PatternMatch.h"
 #include "llvm/ADT/SmallPtrSet.h"
 #include <cstring>
 using namespace llvm;
+using namespace llvm::PatternMatch;
+
+const unsigned MaxDepth = 6;
+
+/// getBitWidth - Returns the bitwidth of the given scalar or pointer type (if
+/// unknown returns 0).  For vector types, returns the element type's bitwidth.
+static unsigned getBitWidth(const Type *Ty, const TargetData *TD) {
+  if (unsigned BitWidth = Ty->getScalarSizeInBits())
+    return BitWidth;
+  assert(isa<PointerType>(Ty) && "Expected a pointer type!");
+  return TD ? TD->getPointerSizeInBits() : 0;
+}
 
 /// ComputeMaskedBits - Determine which of the bits specified in Mask are
 /// known to be either zero or one and return them in the KnownZero/KnownOne
@@ -47,7 +60,6 @@ using namespace llvm;
 void llvm::ComputeMaskedBits(Value *V, const APInt &Mask,
                              APInt &KnownZero, APInt &KnownOne,
                              const TargetData *TD, unsigned Depth) {
-  const unsigned MaxDepth = 6;
   assert(V && "No Value?");
   assert(Depth <= MaxDepth && "Limit Search Depth");
   unsigned BitWidth = Mask.getBitWidth();
@@ -620,6 +632,157 @@ void llvm::ComputeMaskedBits(Value *V, const APInt &Mask,
   }
 }
 
+/// ComputeSignBit - Determine whether the sign bit is known to be zero or
+/// one.  Convenience wrapper around ComputeMaskedBits.
+void llvm::ComputeSignBit(Value *V, bool &KnownZero, bool &KnownOne,
+                          const TargetData *TD, unsigned Depth) {
+  unsigned BitWidth = getBitWidth(V->getType(), TD);
+  if (!BitWidth) {
+    KnownZero = false;
+    KnownOne = false;
+    return;
+  }
+  APInt ZeroBits(BitWidth, 0);
+  APInt OneBits(BitWidth, 0);
+  ComputeMaskedBits(V, APInt::getSignBit(BitWidth), ZeroBits, OneBits, TD,
+                    Depth);
+  KnownOne = OneBits[BitWidth - 1];
+  KnownZero = ZeroBits[BitWidth - 1];
+}
+
+/// isPowerOfTwo - Return true if the given value is known to have exactly one
+/// bit set when defined. For vectors return true if every element is known to
+/// be a power of two when defined.  Supports values with integer or pointer
+/// types and vectors of integers.
+bool llvm::isPowerOfTwo(Value *V, const TargetData *TD, unsigned Depth) {
+  if (ConstantInt *CI = dyn_cast<ConstantInt>(V))
+    return CI->getValue().countPopulation() == 1;
+  // TODO: Handle vector constants.
+
+  // 1 << X is clearly a power of two if the one is not shifted off the end.  If
+  // it is shifted off the end then the result is undefined.
+  if (match(V, m_Shl(m_One(), m_Value())))
+    return true;
+
+  // (signbit) >>l X is clearly a power of two if the one is not shifted off the
+  // bottom.  If it is shifted off the bottom then the result is undefined.
+  ConstantInt *CI;
+  if (match(V, m_LShr(m_ConstantInt(CI), m_Value())) &&
+      CI->getValue().isSignBit())
+    return true;
+
+  // The remaining tests are all recursive, so bail out if we hit the limit.
+  if (Depth++ == MaxDepth)
+    return false;
+
+  if (ZExtInst *ZI = dyn_cast<ZExtInst>(V))
+    return isPowerOfTwo(ZI->getOperand(0), TD, Depth);
+
+  if (SelectInst *SI = dyn_cast<SelectInst>(V))
+    return isPowerOfTwo(SI->getTrueValue(), TD, Depth) &&
+      isPowerOfTwo(SI->getFalseValue(), TD, Depth);
+
+  return false;
+}
+
+/// isKnownNonZero - Return true if the given value is known to be non-zero
+/// when defined.  For vectors return true if every element is known to be
+/// non-zero when defined.  Supports values with integer or pointer type and
+/// vectors of integers.
+bool llvm::isKnownNonZero(Value *V, const TargetData *TD, unsigned Depth) {
+  if (Constant *C = dyn_cast<Constant>(V)) {
+    if (C->isNullValue())
+      return false;
+    if (isa<ConstantInt>(C))
+      // Must be non-zero due to null test above.
+      return true;
+    // TODO: Handle vectors
+    return false;
+  }
+
+  // The remaining tests are all recursive, so bail out if we hit the limit.
+  if (Depth++ == MaxDepth)
+    return false;
+
+  unsigned BitWidth = getBitWidth(V->getType(), TD);
+
+  // X | Y != 0 if X != 0 or Y != 0.
+  Value *X = 0, *Y = 0;
+  if (match(V, m_Or(m_Value(X), m_Value(Y))))
+    return isKnownNonZero(X, TD, Depth) || isKnownNonZero(Y, TD, Depth);
+
+  // ext X != 0 if X != 0.
+  if (isa<SExtInst>(V) || isa<ZExtInst>(V))
+    return isKnownNonZero(cast<Instruction>(V)->getOperand(0), TD, Depth);
+
+  // shl X, A != 0 if X is odd.  Note that the value of the shift is undefined
+  // if the lowest bit is shifted off the end.
+  if (BitWidth && match(V, m_Shl(m_Value(X), m_Value(Y)))) {
+    APInt KnownZero(BitWidth, 0);
+    APInt KnownOne(BitWidth, 0);
+    ComputeMaskedBits(V, APInt(BitWidth, 1), KnownZero, KnownOne, TD, Depth);
+    if (KnownOne[0])
+      return true;
+  }
+  // shr X, A != 0 if X is negative.  Note that the value of the shift is not
+  // defined if the sign bit is shifted off the end.
+  else if (match(V, m_Shr(m_Value(X), m_Value(Y)))) {
+    bool XKnownNonNegative, XKnownNegative;
+    ComputeSignBit(X, XKnownNonNegative, XKnownNegative, TD, Depth);
+    if (XKnownNegative)
+      return true;
+  }
+  // X + Y.
+  else if (match(V, m_Add(m_Value(X), m_Value(Y)))) {
+    bool XKnownNonNegative, XKnownNegative;
+    bool YKnownNonNegative, YKnownNegative;
+    ComputeSignBit(X, XKnownNonNegative, XKnownNegative, TD, Depth);
+    ComputeSignBit(Y, YKnownNonNegative, YKnownNegative, TD, Depth);
+
+    // If X and Y are both non-negative (as signed values) then their sum is not
+    // zero.
+    if (XKnownNonNegative && YKnownNonNegative)
+      return true;
+
+    // If X and Y are both negative (as signed values) then their sum is not
+    // zero unless both X and Y equal INT_MIN.
+    if (BitWidth && XKnownNegative && YKnownNegative) {
+      APInt KnownZero(BitWidth, 0);
+      APInt KnownOne(BitWidth, 0);
+      APInt Mask = APInt::getSignedMaxValue(BitWidth);
+      // The sign bit of X is set.  If some other bit is set then X is not equal
+      // to INT_MIN.
+      ComputeMaskedBits(X, Mask, KnownZero, KnownOne, TD, Depth);
+      if ((KnownOne & Mask) != 0)
+        return true;
+      // The sign bit of Y is set.  If some other bit is set then Y is not equal
+      // to INT_MIN.
+      ComputeMaskedBits(Y, Mask, KnownZero, KnownOne, TD, Depth);
+      if ((KnownOne & Mask) != 0)
+        return true;
+    }
+
+    // The sum of a non-negative number and a power of two is not zero.
+    if (XKnownNonNegative && isPowerOfTwo(Y, TD, Depth))
+      return true;
+    if (YKnownNonNegative && isPowerOfTwo(X, TD, Depth))
+      return true;
+  }
+  // (C ? X : Y) != 0 if X != 0 and Y != 0.
+  else if (SelectInst *SI = dyn_cast<SelectInst>(V)) {
+    if (isKnownNonZero(SI->getTrueValue(), TD, Depth) &&
+        isKnownNonZero(SI->getFalseValue(), TD, Depth))
+      return true;
+  }
+
+  if (!BitWidth) return false;
+  APInt KnownZero(BitWidth, 0);
+  APInt KnownOne(BitWidth, 0);
+  ComputeMaskedBits(V, APInt::getAllOnesValue(BitWidth), KnownZero, KnownOne,
+                    TD, Depth);
+  return KnownOne != 0;
+}
+
 /// MaskedValueIsZero - Return true if 'V & Mask' is known to be zero.  We use
 /// this predicate to simplify operations downstream.  Mask is known to be zero
 /// for bits that V cannot have.

test/Transforms/InstSimplify/2011-01-18-Compare.ll

@@ -27,6 +27,14 @@ define i1 @zext2(i1 %x) {
 ; CHECK: ret i1 %x
 }
 
+define i1 @zext3() {
+; CHECK: @zext3
+  %e = zext i1 1 to i32
+  %c = icmp ne i32 %e, 0
+  ret i1 %c
+; CHECK: ret i1 true
+}
+
 define i1 @sext(i32 %x) {
 ; CHECK: @sext
   %e1 = sext i32 %x to i64
@@ -43,3 +51,49 @@ define i1 @sext2(i1 %x) {
   ret i1 %c
 ; CHECK: ret i1 %x
 }
+
+define i1 @sext3() {
+; CHECK: @sext3
+  %e = sext i1 1 to i32
+  %c = icmp ne i32 %e, 0
+  ret i1 %c
+; CHECK: ret i1 true
+}
+
+define i1 @add(i32 %x, i32 %y) {
+; CHECK: @add
+  %l = lshr i32 %x, 1
+  %r = lshr i32 %y, 1
+  %s = add i32 %l, %r
+  %c = icmp eq i32 %s, 0
+  ret i1 %c
+; CHECK: ret i1 false
+}
+
+define i1 @add2(i8 %x, i8 %y) {
+; CHECK: @add2
+  %l = or i8 %x, 128
+  %r = or i8 %y, 129
+  %s = add i8 %l, %r
+  %c = icmp eq i8 %s, 0
+  ret i1 %c
+; CHECK: ret i1 false
+}
+
+define i1 @addpowtwo(i32 %x, i32 %y) {
+; CHECK: @addpowtwo
+  %l = lshr i32 %x, 1
+  %r = shl i32 1, %y
+  %s = add i32 %l, %r
+  %c = icmp eq i32 %s, 0
+  ret i1 %c
+; CHECK: ret i1 false
+}
+
+define i1 @or(i32 %x) {
+; CHECK: @or
+  %o = or i32 %x, 1
+  %c = icmp eq i32 %o, 0
+  ret i1 %c
+; CHECK: ret i1 false
+}