[llvm] 4a2a6a4 - [ValueTracking] Try to infer range of select from true and false values. (#68256)

[Philip Reames via llvm-commits]

This appears to be unconditional fork.  Given a chain of selects, this 
would appear to fork 2^depth times.  This likely isn't acceptable from a 
compile time perspective.

Unless this was specifically addressed during review, I ask that this 
change be reverted.

Philip

On 10/5/23 10:23, via llvm-commits wrote:
> Author: Mikhail Gudim
> Date: 2023-10-05T13:23:05-04:00
> New Revision: 4a2a6a4111035b4ccd0dce9e6445006f003b88e3
>
> URL: https://github.com/llvm/llvm-project/commit/4a2a6a4111035b4ccd0dce9e6445006f003b88e3
> DIFF: https://github.com/llvm/llvm-project/commit/4a2a6a4111035b4ccd0dce9e6445006f003b88e3.diff
>
> LOG: [ValueTracking] Try to infer range of select from true and false values. (#68256)
>
> When computing range of `select` instruction, first compute the union of
> ranges of "True" and "False" operands of the `select` instruction.
>
> Added:
>      
>
> Modified:
>      llvm/lib/Analysis/ValueTracking.cpp
>      llvm/test/Analysis/BasicAA/range.ll
>      llvm/test/Transforms/InstCombine/binop-select.ll
>
> Removed:
>      
>
>
> ################################################################################
> diff  --git a/llvm/lib/Analysis/ValueTracking.cpp b/llvm/lib/Analysis/ValueTracking.cpp
> index b76becf24d10fc9..f5b18785d4869e0 100644
> --- a/llvm/lib/Analysis/ValueTracking.cpp
> +++ b/llvm/lib/Analysis/ValueTracking.cpp
> @@ -8841,9 +8841,14 @@ ConstantRange llvm::computeConstantRange(const Value *V, bool ForSigned,
>       CR = ConstantRange::getNonEmpty(Lower, Upper);
>     } else if (auto *II = dyn_cast<IntrinsicInst>(V))
>       CR = getRangeForIntrinsic(*II);
> -  else if (auto *SI = dyn_cast<SelectInst>(V))
> -    CR = getRangeForSelectPattern(*SI, IIQ);
> -  else if (isa<FPToUIInst>(V) || isa<FPToSIInst>(V)) {
> +  else if (auto *SI = dyn_cast<SelectInst>(V)) {
> +    ConstantRange CRTrue = computeConstantRange(
> +        SI->getTrueValue(), ForSigned, UseInstrInfo, AC, CtxI, DT, Depth + 1);
> +    ConstantRange CRFalse = computeConstantRange(
> +        SI->getFalseValue(), ForSigned, UseInstrInfo, AC, CtxI, DT, Depth + 1);
> +    CR = CRTrue.unionWith(CRFalse);
> +    CR = CR.intersectWith(getRangeForSelectPattern(*SI, IIQ));
> +  } else if (isa<FPToUIInst>(V) || isa<FPToSIInst>(V)) {
>       APInt Lower = APInt(BitWidth, 0);
>       APInt Upper = APInt(BitWidth, 0);
>       // TODO: Return ConstantRange.
>
> diff  --git a/llvm/test/Analysis/BasicAA/range.ll b/llvm/test/Analysis/BasicAA/range.ll
> index 3862e26ee49a4ba..e5dfb60c8b8784b 100644
> --- a/llvm/test/Analysis/BasicAA/range.ll
> +++ b/llvm/test/Analysis/BasicAA/range.ll
> @@ -2,6 +2,7 @@
>   
>   %struct.S = type { i32, [2 x i32], i32 }
>   %struct.S2 = type { i32, [4 x i32], [4 x i32] }
> + at G = global [10 x i32] zeroinitializer, align 4
>   
>   ; CHECK: Function: t1
>   ; CHECK: NoAlias: i32* %gep1, i32* %gep2
> @@ -258,8 +259,19 @@ join:
>     ret void
>   }
>   
> -declare void @llvm.assume(i1)
>   
> +; CHECK-LABEL: Function: select_in_gep
> +; CHECK: NoAlias: i32* %arrayidx, i32* getelementptr inbounds ([10 x i32], ptr @G, i64 0, i64 3)
> +define i32 @select_in_gep(i1 %c)  {
> +entry:
> +  %select_ = select i1 %c, i64 2, i64 1
> +  %arrayidx = getelementptr inbounds [10 x i32], ptr @G, i64 0, i64 %select_
> +  store i32 42, ptr %arrayidx, align 4
> +  %load_ = load i32, ptr getelementptr inbounds ([10 x i32], ptr @G, i64 0, i64 3), align 4
> +  ret i32 %load_
> +}
> +
> +declare void @llvm.assume(i1)
>   
>   !0 = !{ i32 0, i32 2 }
>   !1 = !{ i32 0, i32 1 }
>
> diff  --git a/llvm/test/Transforms/InstCombine/binop-select.ll b/llvm/test/Transforms/InstCombine/binop-select.ll
> index a59e19897f061d1..6cd4132eadd77b9 100644
> --- a/llvm/test/Transforms/InstCombine/binop-select.ll
> +++ b/llvm/test/Transforms/InstCombine/binop-select.ll
> @@ -324,12 +324,12 @@ define i32 @sub_sel_op1_use(i1 %b) {
>   ; CHECK-LABEL: @sub_sel_op1_use(
>   ; CHECK-NEXT:    [[S:%.*]] = select i1 [[B:%.*]], i32 42, i32 41
>   ; CHECK-NEXT:    call void @use(i32 [[S]])
> -; CHECK-NEXT:    [[R:%.*]] = sub nsw i32 42, [[S]]
> +; CHECK-NEXT:    [[R:%.*]] = sub nuw nsw i32 42, [[S]]
>   ; CHECK-NEXT:    ret i32 [[R]]
>   ;
>     %s = select i1 %b, i32 42, i32 41
>     call void @use(i32 %s)
> -  %r = sub nsw i32 42, %s
> +  %r = sub nuw nsw i32 42, %s
>     ret i32 %r
>   }
>   
>
>
>          
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