[llvm-commits] [llvm] r153747 - /llvm/trunk/lib/Analysis/ValueTracking.cpp

[Rafael Espindola]

Author: rafael
Date: Fri Mar 30 10:52:11 2012
New Revision: 153747

URL: http://llvm.org/viewvc/llvm-project?rev=153747&view=rev
Log:
Add computeMaskedBitsLoad back, as it was the change to instsimplify that
caused the slowdown last time.

Modified:
    llvm/trunk/lib/Analysis/ValueTracking.cpp

Modified: llvm/trunk/lib/Analysis/ValueTracking.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Analysis/ValueTracking.cpp?rev=153747&r1=153746&r2=153747&view=diff
==============================================================================
--- llvm/trunk/lib/Analysis/ValueTracking.cpp (original)
+++ llvm/trunk/lib/Analysis/ValueTracking.cpp Fri Mar 30 10:52:11 2012
@@ -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 @@
     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 @@
   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);