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

[NAKAMURA Takumi]

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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