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

[Redmond, Paul]

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