[llvm] r301880 - [InstSimplify] Handle selects of GEPs with 0 offset

[George Burgess IV via llvm-commits]

reverted by r301885

On Mon, May 1, 2017 at 4:12 PM, George Burgess IV via llvm-commits <
llvm-commits at lists.llvm.org> wrote:

> Author: gbiv
> Date: Mon May  1 18:12:08 2017
> New Revision: 301880
>
> URL: http://llvm.org/viewvc/llvm-project?rev=301880&view=rev
> Log:
> [InstSimplify] Handle selects of GEPs with 0 offset
>
> In particular (since it wouldn't fit nicely in the summary):
> (select (icmp eq V 0) P (getelementptr P V)) -> (getelementptr P V)
>
> Differential Revision: https://reviews.llvm.org/D31435
>
> Modified:
>     llvm/trunk/lib/Analysis/InstructionSimplify.cpp
>     llvm/trunk/test/Transforms/InstSimplify/select.ll
>
> Modified: llvm/trunk/lib/Analysis/InstructionSimplify.cpp
> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/
> Analysis/InstructionSimplify.cpp?rev=301880&r1=301879&r2=301880&view=diff
> ============================================================
> ==================
> --- llvm/trunk/lib/Analysis/InstructionSimplify.cpp (original)
> +++ llvm/trunk/lib/Analysis/InstructionSimplify.cpp Mon May  1 18:12:08
> 2017
> @@ -62,6 +62,8 @@ static Value *SimplifyOrInst(Value *, Va
>  static Value *SimplifyXorInst(Value *, Value *, const SimplifyQuery &,
> unsigned);
>  static Value *SimplifyCastInst(unsigned, Value *, Type *,
>                                 const SimplifyQuery &, unsigned);
> +static Value *SimplifyGEPInst(Type *, ArrayRef<Value *>, const
> SimplifyQuery &,
> +                              unsigned);
>
>  /// For a boolean type or a vector of boolean type, return false or a
> vector
>  /// with every element false.
> @@ -3491,6 +3493,17 @@ static const Value *SimplifyWithOpReplac
>      }
>    }
>
> +  // Same for GEPs.
> +  if (auto *GEP = dyn_cast<GetElementPtrInst>(I)) {
> +    if (MaxRecurse) {
> +      SmallVector<Value *, 8> NewOps(GEP->getNumOperands());
> +      transform(GEP->operands(), NewOps.begin(),
> +                [&](Value *V) { return V == Op ? RepOp : V; });
> +      return SimplifyGEPInst(GEP->getSourceElementType(), NewOps, Q,
> +                             MaxRecurse - 1);
> +    }
> +  }
> +
>    // TODO: We could hand off more cases to instsimplify here.
>
>    // If all operands are constant after substituting Op for RepOp then we
> can
>
> Modified: llvm/trunk/test/Transforms/InstSimplify/select.ll
> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/
> Transforms/InstSimplify/select.ll?rev=301880&r1=301879&r2=301880&view=diff
> ============================================================
> ==================
> --- llvm/trunk/test/Transforms/InstSimplify/select.ll (original)
> +++ llvm/trunk/test/Transforms/InstSimplify/select.ll Mon May  1 18:12:08
> 2017
> @@ -431,3 +431,22 @@ define i8 @do_not_assume_sel_cond(i1 %co
>    ret i8 %sel
>  }
>
> +define i32* @select_icmp_eq_0_gep_operand(i32* %base, i64 %n) {
> +; CHECK-LABEL: @select_icmp_eq_0_gep_operand(
> +; CHECK-NEXT: [[GEP:%.*]] = getelementptr
> +; CHECK-NEXT: ret i32* [[GEP]]
> +  %cond = icmp eq i64 %n, 0
> +  %gep = getelementptr i32, i32* %base, i64 %n
> +  %r = select i1 %cond, i32* %base, i32* %gep
> +  ret i32* %r
> +}
> +
> +define i32* @select_icmp_ne_0_gep_operand(i32* %base, i64 %n) {
> +; CHECK-LABEL: @select_icmp_ne_0_gep_operand(
> +; CHECK-NEXT: [[GEP:%.*]] = getelementptr
> +; CHECK-NEXT: ret i32* [[GEP]]
> +  %cond = icmp ne i64 %n, 0
> +  %gep = getelementptr i32, i32* %base, i64 %n
> +  %r = select i1 %cond, i32* %gep, i32* %base
> +  ret i32* %r
> +}
>
>
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