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

[David Majnemer]

The hope was that I could use it to find where clang might be using undefined behavior and see if it could be fixed.

Sent from my iPhone

On Dec 16, 2012, at 12:13 PM, Evan Cheng <evan.cheng at apple.com> wrote:

> 
> 
> On 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?
> 
> That would be an overly user unfriendly behavior. People do write non-portable code sometimes. :)
> 
> Evan
> 
>> 
>> 
>> 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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>> 
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