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

David Majnemer david.majnemer at gmail.com
Fri Dec 14 10:46:58 PST 2012


Is there a way for us to emit trap instructions if clang uses a left shift
in an undefined mannor?


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
> > +}
> >
> >
> > _______________________________________________
> > llvm-commits mailing list
> > llvm-commits at cs.uiuc.edu
> > http://lists.cs.uiuc.edu/mailman/listinfo/llvm-commits
>
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