Reapply r153423; the original commit was fine. The failing test, distray, had

undefined behavior, which Rafael was kind enough to fix.

Original commit message for r153423:
Use the new range metadata in computeMaskedBits and add a new optimization to
instruction simplify that lets us remove an and when loding a boolean value.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@153521 91177308-0d34-0410-b5e6-96231b3b80d8

2 files changed, 41 insertions, 0 deletions

diff --git a/lib/Analysis/InstructionSimplify.cpp b/lib/Analysis/InstructionSimplify.cpp
index 16e7a72..28400b0 100644
--- a/lib/Analysis/InstructionSimplify.cpp
+++ b/lib/Analysis/InstructionSimplify.cpp
@@ -1370,6 +1370,21 @@ static Value *SimplifyAndInst(Value *Op0, Value *Op1, const Query &Q,
       return Op1;
   }
 
+  unsigned Bitwidth = Op1->getType()->getScalarSizeInBits();
+  APInt DemandedMask = APInt::getAllOnesValue(Bitwidth);
+  APInt KnownZero0 = APInt::getNullValue(Bitwidth);
+  APInt KnownOne0 = APInt::getNullValue(Bitwidth);
+  ComputeMaskedBits(Op0, DemandedMask, KnownZero0, KnownOne0);
+  APInt KnownZero1 = APInt::getNullValue(Bitwidth);
+  APInt KnownOne1 = APInt::getNullValue(Bitwidth);
+  ComputeMaskedBits(Op1, DemandedMask, KnownZero1, KnownOne1);
+
+  if ((KnownZero0 | KnownOne1).isAllOnesValue())
+    return Op0;
+
+  if ((KnownZero1 | KnownOne0).isAllOnesValue())
+    return Op1;
+
   // Try some generic simplifications for associative operations.
   if (Value *V = SimplifyAssociativeBinOp(Instruction::And, Op0, Op1, Q,
                                           MaxRecurse))
diff --git a/lib/Analysis/ValueTracking.cpp b/lib/Analysis/ValueTracking.cpp
index 01e00ca..17bad94 100644
--- a/lib/Analysis/ValueTracking.cpp
+++ b/lib/Analysis/ValueTracking.cpp
@@ -20,8 +20,10 @@
 #include "llvm/GlobalAlias.h"
 #include "llvm/IntrinsicInst.h"
 #include "llvm/LLVMContext.h"
+#include "llvm/Metadata.h"
 #include "llvm/Operator.h"
 #include "llvm/Target/TargetData.h"
+#include "llvm/Support/ConstantRange.h"
 #include "llvm/Support/GetElementPtrTypeIterator.h"
 #include "llvm/Support/MathExtras.h"
 #include "llvm/Support/PatternMatch.h"
@@ -195,6 +197,26 @@ static void ComputeMaskedBitsMul(Value *Op0, Value *Op1, bool NSW,
     KnownOne.setBit(BitWidth - 1);
 }
 
+static void computeMaskedBitsLoad(const MDNode &Ranges, const APInt &Mask,
+                                  APInt &KnownZero) {
+  unsigned BitWidth = Mask.getBitWidth();
+  unsigned NumRanges = Ranges.getNumOperands() / 2;
+  assert(NumRanges >= 1);
+
+  // Use the high end of the ranges to find leading zeros.
+  unsigned MinLeadingZeros = BitWidth;
+  for (unsigned i = 0; i < NumRanges; ++i) {
+    ConstantInt *Lower = cast<ConstantInt>(Ranges.getOperand(2*i + 0));
+    ConstantInt *Upper = cast<ConstantInt>(Ranges.getOperand(2*i + 1));
+    ConstantRange Range(Lower->getValue(), Upper->getValue());
+    if (Range.isWrappedSet())
+      MinLeadingZeros = 0; // -1 has no zeros
+    unsigned LeadingZeros = (Upper->getValue() - 1).countLeadingZeros();
+    MinLeadingZeros = std::min(LeadingZeros, MinLeadingZeros);
+  }
+
+  KnownZero = Mask & APInt::getHighBitsSet(BitWidth, MinLeadingZeros);
+}
 /// ComputeMaskedBits - Determine which of the bits specified in Mask are
 /// known to be either zero or one and return them in the KnownZero/KnownOne
 /// bit sets.  This code only analyzes bits in Mask, in order to short-circuit
@@ -315,6 +337,10 @@ void llvm::ComputeMaskedBits(Value *V, const APInt &Mask,
   APInt KnownZero2(KnownZero), KnownOne2(KnownOne);
   switch (I->getOpcode()) {
   default: break;
+  case Instruction::Load:
+    if (MDNode *MD = cast<LoadInst>(I)->getMetadata(LLVMContext::MD_range))
+      computeMaskedBitsLoad(*MD, Mask, KnownZero);
+    return;
   case Instruction::And: {
     // If either the LHS or the RHS are Zero, the result is zero.
     ComputeMaskedBits(I->getOperand(1), Mask, KnownZero, KnownOne, TD, Depth+1);