Make GetMinTrailingZeros a member function of ScalarEvolution,

so that it can access the TargetData member (when available) and
use ValueTracking.h information to compute information for
SCEVUnknown Values.

Also add GetMinLeadingZeros and GetMinSignBits functions,
with minimal implementations.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@73794 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/include/llvm/Analysis/ScalarEvolution.h b/include/llvm/Analysis/ScalarEvolution.h
index 8c64366c320e5b8e3831fde97721bfc3ddb05ad0..211c0ca5d1201558626a15cc046b8d10b5b24528 100644 (file)
--- a/include/llvm/Analysis/ScalarEvolution.h
+++ b/include/llvm/Analysis/ScalarEvolution.h
@@ -571,6 +571,20 @@ namespace llvm {
     /// is deleted.
     void forgetLoopBackedgeTakenCount(const Loop *L);
 
+    /// GetMinTrailingZeros - Determine the minimum number of zero bits that S is
+    /// guaranteed to end in (at every loop iteration).  It is, at the same time,
+    /// the minimum number of times S is divisible by 2.  For example, given {4,+,8}
+    /// it returns 2.  If S is guaranteed to be 0, it returns the bitwidth of S.
+    uint32_t GetMinTrailingZeros(const SCEVHandle &S);
+
+    /// GetMinLeadingZeros - Determine the minimum number of zero bits that S is
+    /// guaranteed to begin with (at every loop iteration).
+    uint32_t GetMinLeadingZeros(const SCEVHandle &S);
+
+    /// GetMinSignBits - Determine the minimum number of sign bits that S is
+    /// guaranteed to begin with.
+    uint32_t GetMinSignBits(const SCEVHandle &S);
+
     virtual bool runOnFunction(Function &F);
     virtual void releaseMemory();
     virtual void getAnalysisUsage(AnalysisUsage &AU) const;

diff --git a/lib/Analysis/ScalarEvolution.cpp b/lib/Analysis/ScalarEvolution.cpp
index 049f886c5ab3af42a51e8789e79d78a98eaea691..2dab2f367de26ee730606e98fd1e1852fe1fbc8d 100644 (file)
--- a/lib/Analysis/ScalarEvolution.cpp
+++ b/lib/Analysis/ScalarEvolution.cpp
@@ -2294,73 +2294,134 @@ SCEVHandle ScalarEvolution::createNodeForGEP(User *GEP) {
 /// guaranteed to end in (at every loop iteration).  It is, at the same time,
 /// the minimum number of times S is divisible by 2.  For example, given {4,+,8}
 /// it returns 2.  If S is guaranteed to be 0, it returns the bitwidth of S.
-static uint32_t GetMinTrailingZeros(SCEVHandle S, const ScalarEvolution &SE) {
+uint32_t
+ScalarEvolution::GetMinTrailingZeros(const SCEVHandle &S) {
   if (const SCEVConstant *C = dyn_cast<SCEVConstant>(S))
     return C->getValue()->getValue().countTrailingZeros();
 
   if (const SCEVTruncateExpr *T = dyn_cast<SCEVTruncateExpr>(S))
-    return std::min(GetMinTrailingZeros(T->getOperand(), SE),
-                    (uint32_t)SE.getTypeSizeInBits(T->getType()));
+    return std::min(GetMinTrailingZeros(T->getOperand()),
+                    (uint32_t)getTypeSizeInBits(T->getType()));
 
   if (const SCEVZeroExtendExpr *E = dyn_cast<SCEVZeroExtendExpr>(S)) {
-    uint32_t OpRes = GetMinTrailingZeros(E->getOperand(), SE);
-    return OpRes == SE.getTypeSizeInBits(E->getOperand()->getType()) ?
-             SE.getTypeSizeInBits(E->getType()) : OpRes;
+    uint32_t OpRes = GetMinTrailingZeros(E->getOperand());
+    return OpRes == getTypeSizeInBits(E->getOperand()->getType()) ?
+             getTypeSizeInBits(E->getType()) : OpRes;
   }
 
   if (const SCEVSignExtendExpr *E = dyn_cast<SCEVSignExtendExpr>(S)) {
-    uint32_t OpRes = GetMinTrailingZeros(E->getOperand(), SE);
-    return OpRes == SE.getTypeSizeInBits(E->getOperand()->getType()) ?
-             SE.getTypeSizeInBits(E->getType()) : OpRes;
+    uint32_t OpRes = GetMinTrailingZeros(E->getOperand());
+    return OpRes == getTypeSizeInBits(E->getOperand()->getType()) ?
+             getTypeSizeInBits(E->getType()) : OpRes;
   }
 
   if (const SCEVAddExpr *A = dyn_cast<SCEVAddExpr>(S)) {
     // The result is the min of all operands results.
-    uint32_t MinOpRes = GetMinTrailingZeros(A->getOperand(0), SE);
+    uint32_t MinOpRes = GetMinTrailingZeros(A->getOperand(0));
     for (unsigned i = 1, e = A->getNumOperands(); MinOpRes && i != e; ++i)
-      MinOpRes = std::min(MinOpRes, GetMinTrailingZeros(A->getOperand(i), SE));
+      MinOpRes = std::min(MinOpRes, GetMinTrailingZeros(A->getOperand(i)));
     return MinOpRes;
   }
 
   if (const SCEVMulExpr *M = dyn_cast<SCEVMulExpr>(S)) {
     // The result is the sum of all operands results.
-    uint32_t SumOpRes = GetMinTrailingZeros(M->getOperand(0), SE);
-    uint32_t BitWidth = SE.getTypeSizeInBits(M->getType());
+    uint32_t SumOpRes = GetMinTrailingZeros(M->getOperand(0));
+    uint32_t BitWidth = getTypeSizeInBits(M->getType());
     for (unsigned i = 1, e = M->getNumOperands();
          SumOpRes != BitWidth && i != e; ++i)
-      SumOpRes = std::min(SumOpRes + GetMinTrailingZeros(M->getOperand(i), SE),
+      SumOpRes = std::min(SumOpRes + GetMinTrailingZeros(M->getOperand(i)),
                           BitWidth);
     return SumOpRes;
   }
 
   if (const SCEVAddRecExpr *A = dyn_cast<SCEVAddRecExpr>(S)) {
     // The result is the min of all operands results.
-    uint32_t MinOpRes = GetMinTrailingZeros(A->getOperand(0), SE);
+    uint32_t MinOpRes = GetMinTrailingZeros(A->getOperand(0));
     for (unsigned i = 1, e = A->getNumOperands(); MinOpRes && i != e; ++i)
-      MinOpRes = std::min(MinOpRes, GetMinTrailingZeros(A->getOperand(i), SE));
+      MinOpRes = std::min(MinOpRes, GetMinTrailingZeros(A->getOperand(i)));
     return MinOpRes;
   }
 
   if (const SCEVSMaxExpr *M = dyn_cast<SCEVSMaxExpr>(S)) {
     // The result is the min of all operands results.
-    uint32_t MinOpRes = GetMinTrailingZeros(M->getOperand(0), SE);
+    uint32_t MinOpRes = GetMinTrailingZeros(M->getOperand(0));
     for (unsigned i = 1, e = M->getNumOperands(); MinOpRes && i != e; ++i)
-      MinOpRes = std::min(MinOpRes, GetMinTrailingZeros(M->getOperand(i), SE));
+      MinOpRes = std::min(MinOpRes, GetMinTrailingZeros(M->getOperand(i)));
     return MinOpRes;
   }
 
   if (const SCEVUMaxExpr *M = dyn_cast<SCEVUMaxExpr>(S)) {
     // The result is the min of all operands results.
-    uint32_t MinOpRes = GetMinTrailingZeros(M->getOperand(0), SE);
+    uint32_t MinOpRes = GetMinTrailingZeros(M->getOperand(0));
     for (unsigned i = 1, e = M->getNumOperands(); MinOpRes && i != e; ++i)
-      MinOpRes = std::min(MinOpRes, GetMinTrailingZeros(M->getOperand(i), SE));
+      MinOpRes = std::min(MinOpRes, GetMinTrailingZeros(M->getOperand(i)));
     return MinOpRes;
   }
 
-  // SCEVUDivExpr, SCEVUnknown
+  if (const SCEVUnknown *U = dyn_cast<SCEVUnknown>(S)) {
+    // For a SCEVUnknown, ask ValueTracking.
+    unsigned BitWidth = getTypeSizeInBits(U->getType());
+    APInt Mask = APInt::getAllOnesValue(BitWidth);
+    APInt Zeros(BitWidth, 0), Ones(BitWidth, 0);
+    ComputeMaskedBits(U->getValue(), Mask, Zeros, Ones);
+    return Zeros.countTrailingOnes();
+  }
+
+  // SCEVUDivExpr
   return 0;
 }
 
+uint32_t
+ScalarEvolution::GetMinLeadingZeros(const SCEVHandle &S) {
+  // TODO: Handle other SCEV expression types here.
+
+  if (const SCEVConstant *C = dyn_cast<SCEVConstant>(S))
+    return C->getValue()->getValue().countLeadingZeros();
+
+  if (const SCEVZeroExtendExpr *C = dyn_cast<SCEVZeroExtendExpr>(S)) {
+    // A zero-extension cast adds zero bits.
+    return GetMinLeadingZeros(C->getOperand()) +
+           (getTypeSizeInBits(C->getType()) -
+            getTypeSizeInBits(C->getOperand()->getType()));
+  }
+
+  if (const SCEVUnknown *U = dyn_cast<SCEVUnknown>(S)) {
+    // For a SCEVUnknown, ask ValueTracking.
+    unsigned BitWidth = getTypeSizeInBits(U->getType());
+    APInt Mask = APInt::getAllOnesValue(BitWidth);
+    APInt Zeros(BitWidth, 0), Ones(BitWidth, 0);
+    ComputeMaskedBits(U->getValue(), Mask, Zeros, Ones, TD);
+    return Zeros.countLeadingOnes();
+  }
+
+  return 1;
+}
+
+uint32_t
+ScalarEvolution::GetMinSignBits(const SCEVHandle &S) {
+  // TODO: Handle other SCEV expression types here.
+
+  if (const SCEVConstant *C = dyn_cast<SCEVConstant>(S)) {
+    const APInt &A = C->getValue()->getValue();
+    return A.isNegative() ? A.countLeadingOnes() :
+                            A.countLeadingZeros();
+  }
+
+  if (const SCEVSignExtendExpr *C = dyn_cast<SCEVSignExtendExpr>(S)) {
+    // A sign-extension cast adds sign bits.
+    return GetMinSignBits(C->getOperand()) +
+           (getTypeSizeInBits(C->getType()) -
+            getTypeSizeInBits(C->getOperand()->getType()));
+  }
+
+  if (const SCEVUnknown *U = dyn_cast<SCEVUnknown>(S)) {
+    // For a SCEVUnknown, ask ValueTracking.
+    return ComputeNumSignBits(U->getValue(), TD);
+  }
+
+  return 1;
+}
+
 /// createSCEV - We know that there is no SCEV for the specified value.
 /// Analyze the expression.
 ///
@@ -2430,7 +2491,7 @@ SCEVHandle ScalarEvolution::createSCEV(Value *V) {
     if (ConstantInt *CI = dyn_cast<ConstantInt>(U->getOperand(1))) {
       SCEVHandle LHS = getSCEV(U->getOperand(0));
       const APInt &CIVal = CI->getValue();
-      if (GetMinTrailingZeros(LHS, *this) >=
+      if (GetMinTrailingZeros(LHS) >=
           (CIVal.getBitWidth() - CIVal.countLeadingZeros()))
         return getAddExpr(LHS, getSCEV(U->getOperand(1)));
     }