[llvm] r185954 - ValueTracking: Fix bugs in isKnownToBeAPowerOfTwo

[Hal Finkel]

----- Original Message -----
> ----- Original Message -----
> > Author: majnemer
> > Date: Tue Jul  9 13:11:10 2013
> > New Revision: 185954
> > 
> > URL: http://llvm.org/viewvc/llvm-project?rev=185954&view=rev
> > Log:
> > ValueTracking: Fix bugs in isKnownToBeAPowerOfTwo
> > 
> > (add nsw x, (and x, y)) isn't a power of two if x is zero, it's
> > zero
> 
> I don't think that this requires nsw:

Never mind; I forgot about the orZero requirement. :(

 -Hal

> 
> cvc4 1.2 assertions:off
> CVC4> OPTION "produce-models";
> CVC4> x, y : BITVECTOR(32);
> CVC4> ISPOW2 : BITVECTOR(32) -> BOOLEAN = LAMBDA(x : BITVECTOR(32)):
> BVPLUS(32, x, 0hexffffffff) & x = 0hex00000000;
> CVC4> ASSERT ISPOW2(x);
> CVC4> QUERY(ISPOW2(BVPLUS(32, x, x & y)));
> valid
> 
> > (add nsw x, (xor x, y)) isn't a power of two if y has bits set that
> > aren't set in x
> 
> And neither does this:
> 
> cvc4 1.2 assertions:off
> CVC4> OPTION "produce-models";
> CVC4> x, y : BITVECTOR(32);
> CVC4> ISPOW2 : BITVECTOR(32) -> BOOLEAN = LAMBDA(x : BITVECTOR(32)):
> BVPLUS(32, x, 0hexffffffff) & x = 0hex00000000;
> CVC4> ASSERT ISPOW2(x);
> CVC4> ASSERT(~x & y = 0hex00000000);
> CVC4> QUERY(ISPOW2(BVPLUS(32, x, BVXOR(x,y))));
> valid
> 
>  -Hal
> 
> > 
> > Modified:
> >     llvm/trunk/lib/Analysis/ValueTracking.cpp
> >     llvm/trunk/test/Transforms/InstCombine/rem.ll
> > 
> > Modified: llvm/trunk/lib/Analysis/ValueTracking.cpp
> > URL:
> > http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Analysis/ValueTracking.cpp?rev=185954&r1=185953&r2=185954&view=diff
> > ==============================================================================
> > --- llvm/trunk/lib/Analysis/ValueTracking.cpp (original)
> > +++ llvm/trunk/lib/Analysis/ValueTracking.cpp Tue Jul  9 13:11:10
> > 2013
> > @@ -861,16 +861,14 @@ bool llvm::isKnownToBeAPowerOfTwo(Value
> >          // Adding a power of two to the same power of two is a
> >          power
> >          of two or
> >          // zero.
> >          if (BinaryOperator *XBO = dyn_cast<BinaryOperator>(X))
> > -          if (XBO->getOpcode() == Instruction::And ||
> > -              XBO->getOpcode() == Instruction::Xor)
> > +          if (XBO->getOpcode() == Instruction::And)
> >              if (XBO->getOperand(0) == Y || XBO->getOperand(1) ==
> >              Y)
> > -              if (isKnownToBeAPowerOfTwo(Y, /*OrZero*/true,
> > Depth))
> > +              if (isKnownToBeAPowerOfTwo(Y, OrZero, Depth))
> >                  return true;
> >          if (BinaryOperator *YBO = dyn_cast<BinaryOperator>(Y))
> > -          if (YBO->getOpcode() == Instruction::And ||
> > -              YBO->getOpcode() == Instruction::Xor)
> > +          if (YBO->getOpcode() == Instruction::And)
> >              if (YBO->getOperand(0) == X || YBO->getOperand(1) ==
> >              X)
> > -              if (isKnownToBeAPowerOfTwo(X, /*OrZero*/true,
> > Depth))
> > +              if (isKnownToBeAPowerOfTwo(X, OrZero, Depth))
> >                  return true;
> >        }
> >  
> > 
> > Modified: llvm/trunk/test/Transforms/InstCombine/rem.ll
> > URL:
> > http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/InstCombine/rem.ll?rev=185954&r1=185953&r2=185954&view=diff
> > ==============================================================================
> > --- llvm/trunk/test/Transforms/InstCombine/rem.ll (original)
> > +++ llvm/trunk/test/Transforms/InstCombine/rem.ll Tue Jul  9
> > 13:11:10
> > 2013
> > @@ -163,18 +163,3 @@ define i32 @test16(i32 %x, i32 %y) {
> >  	%rem = urem i32 %x, %add
> >  	ret i32 %rem
> >  }
> > -
> > -define i32 @test17(i16 %x, i32 %y) {
> > -; CHECK: @test17
> > -; CHECK-NEXT: [[AND:%.*]] = and i16 %x, 4
> > -; CHECK-NEXT: [[EXT:%.*]] = zext i16 [[AND]] to i32
> > -; CHECK-NEXT: [[SHL:%.*]] = shl nuw nsw i32 [[EXT]], 3
> > -; CHECK-NEXT: [[XOR:%.*]] = xor i32 [[SHL]], 63
> > -; CHECK-NEXT: [[REM:%.*]] = and i32 [[XOR]], %y
> > -; CHECK-NEXT: ret i32 [[REM]]
> > -	%1 = and i16 %x, 4
> > -	%2 = icmp ne i16 %1, 0
> > -	%3 = select i1 %2, i32 32, i32 64
> > -	%4 = urem i32 %y, %3
> > -	ret i32 %4
> > -}
> > 
> > 
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> > 
> 
> --
> Hal Finkel
> Assistant Computational Scientist
> Leadership Computing Facility
> Argonne National Laboratory
> _______________________________________________
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> llvm-commits at cs.uiuc.edu
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> 

-- 
Hal Finkel
Assistant Computational Scientist
Leadership Computing Facility
Argonne National Laboratory