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

[Michael Ilseman]

On 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
> 

David, could either you or Takumi add in a test to test/Transforms/InstCombine that would expose this breakage?

> 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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