[llvm-commits] [llvm] r170020 - in /llvm/trunk: lib/Transforms/InstCombine/InstCombineCompares.cpp test/Transforms/InstCombine/icmp.ll

[David Blaikie]

On Fri, Dec 14, 2012 at 10:46 AM, David Majnemer
<david.majnemer at gmail.com> wrote:
> Is there a way for us to emit trap instructions if clang uses a left shift
> in an undefined mannor?

This sort of check could be added to ubsan if it's not already.
(+Richard Smith who's working on that)

- David

>
>
> On Thu, Dec 13, 2012 at 6:39 AM, NAKAMURA Takumi <geek4civic at gmail.com>
> wrote:
>>
>> David, excuse me, I have reverted it in r170128 to unbreak selfhosting.
>>
>> It seems isKnownToBeAPowerOfTwo(X) assumes (1 << n) always non-zero.
>> (It might be "non-zero, or undefined")
>>
>> FYI, http://bb.pgr.jp/builders/clang-3stage-x86_64-linux/builds/271
>>
>> I am investigating "undefined behavior" in clang.
>>
>> ...Takumi
>>
>> 2012/12/13 David Majnemer <david.majnemer at gmail.com>:
>> > Author: majnemer
>> > Date: Wed Dec 12 14:48:54 2012
>> > New Revision: 170020
>> >
>> > URL: http://llvm.org/viewvc/llvm-project?rev=170020&view=rev
>> > Log:
>> > Simplify negated bit test
>> >
>> > Modified:
>> >     llvm/trunk/lib/Transforms/InstCombine/InstCombineCompares.cpp
>> >     llvm/trunk/test/Transforms/InstCombine/icmp.ll
>> >
>> > Modified: llvm/trunk/lib/Transforms/InstCombine/InstCombineCompares.cpp
>> > URL:
>> > http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/InstCombine/InstCombineCompares.cpp?rev=170020&r1=170019&r2=170020&view=diff
>> >
>> > ==============================================================================
>> > --- llvm/trunk/lib/Transforms/InstCombine/InstCombineCompares.cpp
>> > (original)
>> > +++ llvm/trunk/lib/Transforms/InstCombine/InstCombineCompares.cpp Wed
>> > Dec 12 14:48:54 2012
>> > @@ -2034,6 +2034,15 @@
>> >
>> > CI->countTrailingZeros()));
>> >        }
>> >
>> > +      // Turn x&~y == 0 into x&y != 0 if x is a power of 2.
>> > +      Value *X = 0, *Y = 0;
>> > +      if (match(Op0, m_And(m_Value(X), m_Not(m_Value(Y)))) &&
>> > +          match(Op1, m_Zero()) && isPowerOfTwo(X, TD)) {
>> > +        return new ICmpInst(ICmpInst::ICMP_NE,
>> > +                            Builder->CreateAnd(X, Y),
>> > +                            Op1);
>> > +      }
>> > +
>> >        break;
>> >      }
>> >      case ICmpInst::ICMP_NE: {
>> > @@ -2071,6 +2080,15 @@
>> >
>> > CI->countTrailingZeros()));
>> >        }
>> >
>> > +      // Turn x&~y != 0 into x&y == 0 if x is a power of 2.
>> > +      Value *X = 0, *Y = 0;
>> > +      if (match(Op0, m_And(m_Value(X), m_Not(m_Value(Y)))) &&
>> > +          match(Op1, m_Zero()) && isPowerOfTwo(X, TD)) {
>> > +        return new ICmpInst(ICmpInst::ICMP_EQ,
>> > +                            Builder->CreateAnd(X, Y),
>> > +                            Op1);
>> > +      }
>> > +
>> >        break;
>> >      }
>> >      case ICmpInst::ICMP_ULT:
>> >
>> > Modified: llvm/trunk/test/Transforms/InstCombine/icmp.ll
>> > URL:
>> > http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/InstCombine/icmp.ll?rev=170020&r1=170019&r2=170020&view=diff
>> >
>> > ==============================================================================
>> > --- llvm/trunk/test/Transforms/InstCombine/icmp.ll (original)
>> > +++ llvm/trunk/test/Transforms/InstCombine/icmp.ll Wed Dec 12 14:48:54
>> > 2012
>> > @@ -677,3 +677,29 @@
>> >  ; CHECK-NEXT: ret i1 true
>> >    ret i1 %cmp
>> >  }
>> > +
>> > +define i1 @test67(i32 %A, i32 %B) {
>> > +  %neg = xor i32 %A, -1
>> > +  %shl = shl i32 1, %B
>> > +  %and = and i32 %shl, %neg
>> > +  %cmp = icmp ne i32 %and, 0
>> > +; CHECK: @test67
>> > +; CHECK-NEXT: %shl = shl i32 1, %B
>> > +; CHECK-NEXT: %1 = and i32 %shl, %A
>> > +; CHECK-NEXT: %cmp = icmp eq i32 %1, 0
>> > +; CHECK-NEXT: ret i1 %cmp
>> > +  ret i1 %cmp
>> > +}
>> > +
>> > +define i1 @test68(i32 %A, i32 %B) {
>> > +  %neg = xor i32 %A, -1
>> > +  %shl = shl i32 1, %B
>> > +  %and = and i32 %shl, %neg
>> > +  %cmp = icmp eq i32 %and, 0
>> > +; CHECK: @test68
>> > +; CHECK-NEXT: %shl = shl i32 1, %B
>> > +; CHECK-NEXT: %1 = and i32 %shl, %A
>> > +; CHECK-NEXT: %cmp = icmp ne i32 %1, 0
>> > +; CHECK-NEXT: ret i1 %cmp
>> > +  ret i1 %cmp
>> > +}
>> >
>> >
>> > _______________________________________________
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>> > llvm-commits at cs.uiuc.edu
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>
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