[llvm-commits] [llvm] r170576 - in /llvm/trunk: lib/Target/X86/README.txt lib/Transforms/InstCombine/InstCombineCompares.cpp test/Transforms/InstCombine/icmp.ll

[Nadav Rotem]

Okay, I can see that Duncan reviewed it.  Thanks. 

On Dec 19, 2012, at 12:15 PM, "Redmond, Paul" <paul.redmond at intel.com> wrote:

> Sorry, I should reply to the thread on llvm-dev--the patch was reviewed there.
> 
> paul
> 
> On 2012-12-19, at 3:04 PM, Nadav Rotem wrote:
> 
>> code review ?
>> 
>> On Dec 19, 2012, at 11:47 AM, Paul Redmond <paul.redmond at intel.com> wrote:
>> 
>>> Author: predmond
>>> Date: Wed Dec 19 13:47:13 2012
>>> New Revision: 170576
>>> 
>>> URL: http://llvm.org/viewvc/llvm-project?rev=170576&view=rev
>>> Log:
>>> Transform (x&C)>V into (x&C)!=0 where possible
>>> 
>>> When the least bit of C is greater than V, (x&C) must be greater than V
>>> if it is not zero, so the comparison can be simplified.
>>> 
>>> Although this was suggested in Target/X86/README.txt, it benefits any
>>> architecture with a directly testable form of AND.
>>> 
>>> Patch by Kevin Schoedel
>>> 
>>> Modified:
>>>  llvm/trunk/lib/Target/X86/README.txt
>>>  llvm/trunk/lib/Transforms/InstCombine/InstCombineCompares.cpp
>>>  llvm/trunk/test/Transforms/InstCombine/icmp.ll
>>> 
>>> Modified: llvm/trunk/lib/Target/X86/README.txt
>>> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Target/X86/README.txt?rev=170576&r1=170575&r2=170576&view=diff
>>> ==============================================================================
>>> --- llvm/trunk/lib/Target/X86/README.txt (original)
>>> +++ llvm/trunk/lib/Target/X86/README.txt Wed Dec 19 13:47:13 2012
>>> @@ -1568,43 +1568,6 @@
>>> Core 2, and "Generic"
>>> 
>>> //===---------------------------------------------------------------------===//
>>> -
>>> -Testcase:
>>> -int a(int x) { return (x & 127) > 31; }
>>> -
>>> -Current output:
>>> -	movl	4(%esp), %eax
>>> -	andl	$127, %eax
>>> -	cmpl	$31, %eax
>>> -	seta	%al
>>> -	movzbl	%al, %eax
>>> -	ret
>>> -
>>> -Ideal output:
>>> -	xorl	%eax, %eax
>>> -	testl	$96, 4(%esp)
>>> -	setne	%al
>>> -	ret
>>> -
>>> -This should definitely be done in instcombine, canonicalizing the range
>>> -condition into a != condition.  We get this IR:
>>> -
>>> -define i32 @a(i32 %x) nounwind readnone {
>>> -entry:
>>> -	%0 = and i32 %x, 127		; <i32> [#uses=1]
>>> -	%1 = icmp ugt i32 %0, 31		; <i1> [#uses=1]
>>> -	%2 = zext i1 %1 to i32		; <i32> [#uses=1]
>>> -	ret i32 %2
>>> -}
>>> -
>>> -Instcombine prefers to strength reduce relational comparisons to equality
>>> -comparisons when possible, this should be another case of that.  This could
>>> -be handled pretty easily in InstCombiner::visitICmpInstWithInstAndIntCst, but it
>>> -looks like InstCombiner::visitICmpInstWithInstAndIntCst should really already
>>> -be redesigned to use ComputeMaskedBits and friends.
>>> -
>>> -
>>> -//===---------------------------------------------------------------------===//
>>> Testcase:
>>> int x(int a) { return (a&0xf0)>>4; }
>>> 
>>> 
>>> Modified: llvm/trunk/lib/Transforms/InstCombine/InstCombineCompares.cpp
>>> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/InstCombine/InstCombineCompares.cpp?rev=170576&r1=170575&r2=170576&view=diff
>>> ==============================================================================
>>> --- llvm/trunk/lib/Transforms/InstCombine/InstCombineCompares.cpp (original)
>>> +++ llvm/trunk/lib/Transforms/InstCombine/InstCombineCompares.cpp Wed Dec 19 13:47:13 2012
>>> @@ -1226,6 +1226,16 @@
>>>       ICI.setOperand(0, NewAnd);
>>>       return &ICI;
>>>     }
>>> +
>>> +      // Replace ((X & AndCST) > RHSV) with ((X & AndCST) != 0), if any
>>> +      // bit set in (X & AndCST) will produce a result greater than RHSV.
>>> +      if (ICI.getPredicate() == ICmpInst::ICMP_UGT) {
>>> +        unsigned NTZ = AndCST->getValue().countTrailingZeros();
>>> +        if ((NTZ < AndCST->getBitWidth()) &&
>>> +            APInt::getOneBitSet(AndCST->getBitWidth(), NTZ).ugt(RHSV))
>>> +          return new ICmpInst(ICmpInst::ICMP_NE, LHSI,
>>> +                              Constant::getNullValue(RHS->getType()));
>>> +      }
>>>   }
>>> 
>>>   // Try to optimize things like "A[i]&42 == 0" to index computations.
>>> 
>>> Modified: llvm/trunk/test/Transforms/InstCombine/icmp.ll
>>> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/InstCombine/icmp.ll?rev=170576&r1=170575&r2=170576&view=diff
>>> ==============================================================================
>>> --- llvm/trunk/test/Transforms/InstCombine/icmp.ll (original)
>>> +++ llvm/trunk/test/Transforms/InstCombine/icmp.ll Wed Dec 19 13:47:13 2012
>>> @@ -677,3 +677,20 @@
>>> ; CHECK-NEXT: ret i1 true
>>> ret i1 %cmp
>>> }
>>> +
>>> +; CHECK: @test67
>>> +; CHECK: %and = and i32 %x, 96
>>> +; CHECK: %cmp = icmp ne i32 %and, 0
>>> +define i1 @test67(i32 %x) nounwind uwtable {
>>> +  %and = and i32 %x, 127
>>> +  %cmp = icmp sgt i32 %and, 31
>>> +  ret i1 %cmp
>>> +}
>>> +
>>> +; CHECK: @test68
>>> +; CHECK: %cmp = icmp ugt i32 %and, 30
>>> +define i1 @test68(i32 %x) nounwind uwtable {
>>> +  %and = and i32 %x, 127
>>> +  %cmp = icmp sgt i32 %and, 30
>>> +  ret i1 %cmp
>>> +}
>>> 
>>> 
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>> 
>