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

[Nadav Rotem]

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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