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

[George Burgess IV via llvm-commits]

(+davide -- fyi)

Relanded in r330667

On Mon, May 1, 2017 at 5:08 PM, George Burgess IV <
george.burgess.iv at gmail.com> wrote:

> 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/Transfor
>> ms/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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>
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