search for: knownon

I'm trying to reason about how to find certain bit positions of the absolute value of a given integer value. Specifically, I want to know the highest possibly set bit and lowest possibly set bit of the absolute value, in order to find the range between the two. Note that I'm specifically trying to be as conservative as possible. This is what I have so far: If the sign bit of the

...== idx => 3 == 2*idx and you've generalized this slightly to make this: (odd number) == 2*idx which makes sense. I think that we can go further looking at: n == 2*idx and, calling computeKnownBits on n and idx, then asking whether: knownZeros(n) == (knownZeros(idx) << 1) | 1 and knownOnes(n) == knownOnes(idx) << 1 (please note the comment in aliasSameBasePointerGEPs regarding avoiding PR32314) also, if we have more than one array access, we can have: n - idx == m - idx then we have: n-m == 2*idx and so we can check: knownZeros(n-m) == (knownZeros(idx) << 1) | 1...

...p (revision 125281) +++ lib/Analysis/ValueTracking.cpp (working copy) @@ -593,6 +593,8 @@ // Otherwise take the unions of the known bit sets of the operands, // taking conservative care to avoid excessive recursion. if (Depth < MaxDepth - 1 && !KnownZero && !KnownOne) { + if (!P->getNumIncomingValues()) + return; KnownZero = APInt::getAllOnesValue(BitWidth); KnownOne = APInt::getAllOnesValue(BitWidth); for (unsigned i = 0, e = P->getNumIncomingValues(); i != e; ++i) { -- Jakub Staszak

...s to apply to some later revision. Anyway, I actually located the real bug. Right at the end of InstCombiner::SimplifyDemandedUseBits, there's this piece of code: // If the client is only demanding bits that we know, return the known // constant. if ((DemandedMask & (RHSKnownZero|RHSKnownOne)) == DemandedMask) { Constant *C = Context->getConstantInt(RHSKnownOne); if (isa<PointerType>(V->getType())) C = Context->getConstantExprIntToPtr(C, V->getType()); return C; } return false; } Note that C is a scalar integer, and so when V is actually a vect...

Hello All, I have met one may-alias case from llvm's alias analysis. The code snippet is as following: char buf[4]; void test (int idx) { char *a = &buf[3 - idx]; char *b = &buf[idx]; *a = 1; *b = 2; } I can see below output from alias set tracker for above code snippet. Alias sets for function 'test': Alias Set Tracker: 1 alias sets for 2 pointer values.  

...evision. > Anyway, I actually located the real bug. Right at the end of > InstCombiner::SimplifyDemandedUseBits, there's this piece of code: > >  // If the client is only demanding bits that we know, return the known >  // constant. >  if ((DemandedMask & (RHSKnownZero|RHSKnownOne)) == DemandedMask) { >    Constant *C = Context->getConstantInt(RHSKnownOne); >    if (isa<PointerType>(V->getType())) >      C = Context->getConstantExprIntToPtr(C, V->getType()); >    return C; >  } >  return false; > } > > Note that C is a scalar int...

Can someone explain what this function is supposed to do? I've looked at PowerPC, Sparc, etc.. and can't really figure out what I should be doing here. Thanks, Micah Villmow Systems Engineer Advanced Technology & Performance Advanced Micro Devices Inc. 4555 Great America Pkwy, Santa Clara, CA. 95054 P: 408-572-6219 F: 408-572-6596 -------------- next part

...i -------------- next part -------------- Index: InstructionCombining.cpp =================================================================== --- InstructionCombining.cpp (revision 77486) +++ InstructionCombining.cpp (working copy) @@ -1014,7 +1014,7 @@ if ((DemandedMask & (RHSKnownZero|RHSKnownOne)) == DemandedMask) { // all known if ((RHSKnownOne & LHSKnownOne) == RHSKnownOne) { - Constant *AndC = ConstantInt::get(*Context, + Constant *AndC = ConstantInt::get(VTy, ~RHSKnownOne & DemandedMask); Instru...

Hi All, I found a regression which triggers the asserts: "Binary operator types must match!" and "Op types should be identical!". It's happening with a piece of vector code, and the asserts happen because a logic operation is attempted between a vector and a scalar (which is not present in the original code, but created by InstCombine). It's caused by revision

On Wed, May 20, 2009 at 4:55 PM, Dan Gohman <gohman at apple.com> wrote: > Can you explain why you chose the approach of using a new pass? > I pictured removing LegalizeDAG's type legalization code would > mostly consist of finding all the places that use TLI.getTypeAction > and just deleting code for handling its Expand and Promote. Are you > anticipating something more

On May 20, 2009, at 1:34 PM, Eli Friedman wrote: > On Wed, May 20, 2009 at 1:19 PM, Eli Friedman > <eli.friedman at gmail.com> wrote: > >> Per subject, this patch adding an additional pass to handle vector >> >> operations; the idea is that this allows removing the code from >> >> LegalizeDAG that handles illegal types, which should be a significant

...- return true; - } - } - - // Okay, the shift amount isn't constant. However, if we can tell that it is - // >= 32 or < 32, we can still simplify it, without knowing the actual value. - APInt Mask = APInt::getHighBitsSet(ShBits, ShBits - Log2_32(NVTBits)); - APInt KnownZero, KnownOne; - DAG.ComputeMaskedBits(Amt, Mask, KnownZero, KnownOne); - - // If we know that if any of the high bits of the shift amount are one, then - // we can do this as a couple of simple shifts. - if (KnownOne.intersects(Mask)) { - // Mask out the high bit, which we know is set. - Amt = DAG.ge...