[llvm] 5a6e66e - [InstCombine] add folds for icmp+ctpop

[Philip Reames via llvm-commits]

Are you going to handle other variants?  A few of potentials...

ctpop(X) != 0 ==> X != 0.

ctpop(X) == C ==> X != C2 where all but one bit in X is known

ctpop(X) > C ==> X & (C2) != 0 where C bits of X are known one and C2 is 
the inverse known zero mask.

Philip

On 10/26/20 1:49 PM, Sanjay Patel via llvm-commits wrote:
> Author: Sanjay Patel
> Date: 2020-10-26T16:48:56-04:00
> New Revision: 5a6e66ec72382d370046e04c415f8c3cb7e8b68d
>
> URL: https://github.com/llvm/llvm-project/commit/5a6e66ec72382d370046e04c415f8c3cb7e8b68d
> DIFF: https://github.com/llvm/llvm-project/commit/5a6e66ec72382d370046e04c415f8c3cb7e8b68d.diff
>
> LOG: [InstCombine] add folds for icmp+ctpop
>
> https://alive2.llvm.org/ce/z/XjFPQJ
>
>    define void @src(i64 %value) {
>      %t0 = call i64 @llvm.ctpop.i64(i64 %value)
>      %gt = icmp ugt i64 %t0, 63
>      %lt = icmp ult i64 %t0, 64
>      call void @use(i1 %gt, i1 %lt)
>      ret void
>    }
>
>    define void @tgt(i64 %value) {
>      %eq = icmp eq i64 %value, -1
>      %ne = icmp ne i64 %value, -1
>      call void @use(i1 %eq, i1 %ne)
>      ret void
>    }
>
>    declare i64 @llvm.ctpop.i64(i64) #1
>    declare void @use(i1, i1)
>
> Added:
>      
>
> Modified:
>      llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
>      llvm/test/Transforms/InstCombine/cmp-intrinsic.ll
>
> Removed:
>      
>
>
> ################################################################################
> diff  --git a/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp b/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
> index 24713d7681b2..fe342dc2fc6c 100644
> --- a/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
> +++ b/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
> @@ -3174,6 +3174,18 @@ Instruction *InstCombinerImpl::foldICmpIntrinsicWithConstant(ICmpInst &Cmp,
>     unsigned BitWidth = C.getBitWidth();
>     ICmpInst::Predicate Pred = Cmp.getPredicate();
>     switch (II->getIntrinsicID()) {
> +  case Intrinsic::ctpop: {
> +    // (ctpop X > BitWidth - 1) --> X == -1
> +    Value *X = II->getArgOperand(0);
> +    if (C == BitWidth - 1 && Pred == ICmpInst::ICMP_UGT)
> +      return CmpInst::Create(Instruction::ICmp, ICmpInst::ICMP_EQ, X,
> +                             ConstantInt::getAllOnesValue(Ty));
> +    // (ctpop X < BitWidth) --> X != -1
> +    if (C == BitWidth && Pred == ICmpInst::ICMP_ULT)
> +      return CmpInst::Create(Instruction::ICmp, ICmpInst::ICMP_NE, X,
> +                             ConstantInt::getAllOnesValue(Ty));
> +    break;
> +  }
>     case Intrinsic::ctlz: {
>       // ctlz(0bXXXXXXXX) > 3 -> 0bXXXXXXXX < 0b00010000
>       if (Pred == ICmpInst::ICMP_UGT && C.ult(BitWidth)) {
>
> diff  --git a/llvm/test/Transforms/InstCombine/cmp-intrinsic.ll b/llvm/test/Transforms/InstCombine/cmp-intrinsic.ll
> index 6519eda41499..599a749954d2 100644
> --- a/llvm/test/Transforms/InstCombine/cmp-intrinsic.ll
> +++ b/llvm/test/Transforms/InstCombine/cmp-intrinsic.ll
> @@ -495,7 +495,7 @@ define i1 @ctpop_ugt_bitwidth_minus_one_i8(i8 %x, i8* %p) {
>   ; CHECK-LABEL: @ctpop_ugt_bitwidth_minus_one_i8(
>   ; CHECK-NEXT:    [[POP:%.*]] = tail call i8 @llvm.ctpop.i8(i8 [[X:%.*]]), [[RNG2:!range !.*]]
>   ; CHECK-NEXT:    store i8 [[POP]], i8* [[P:%.*]], align 1
> -; CHECK-NEXT:    [[CMP:%.*]] = icmp ugt i8 [[POP]], 7
> +; CHECK-NEXT:    [[CMP:%.*]] = icmp eq i8 [[X]], -1
>   ; CHECK-NEXT:    ret i1 [[CMP]]
>   ;
>     %pop = tail call i8 @llvm.ctpop.i8(i8 %x)
> @@ -506,8 +506,7 @@ define i1 @ctpop_ugt_bitwidth_minus_one_i8(i8 %x, i8* %p) {
>   
>   define <2 x i1> @ctpop_ult_bitwidth_v2i32(<2 x i32> %x) {
>   ; CHECK-LABEL: @ctpop_ult_bitwidth_v2i32(
> -; CHECK-NEXT:    [[POP:%.*]] = tail call <2 x i32> @llvm.ctpop.v2i32(<2 x i32> [[X:%.*]])
> -; CHECK-NEXT:    [[CMP:%.*]] = icmp ult <2 x i32> [[POP]], <i32 32, i32 32>
> +; CHECK-NEXT:    [[CMP:%.*]] = icmp ne <2 x i32> [[X:%.*]], <i32 -1, i32 -1>
>   ; CHECK-NEXT:    ret <2 x i1> [[CMP]]
>   ;
>     %pop = tail call <2 x i32> @llvm.ctpop.v2i32(<2 x i32> %x)
>
>
>          
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