[InstCombine] Remove an unnecessary/broken gep combine

[nagisa]

Summary

In preparation for D98120: [InstCombine] Remove a provenance changing gep transformation.

[nagisa]

Remove the other combine too, its broken as well…

llvm/lib/Transforms/InstCombine/InstructionCombining.cpp

if (GEP.getOperand(1)->getType()->getScalarSizeInBits() ==
           Matched = true;
       } else if (match(GEP.getOperand(1),
                        m_SDiv(m_Value(V), m_ConstantInt(C)))) {
         if (TyAllocSize == C)
           Matched = true;
       }
 
       if (Matched) {
-        // Canonicalize (gep i8* X, -(ptrtoint Y))
-        // to (inttoptr (sub (ptrtoint X), (ptrtoint Y)))
-        // The GEP pattern is emitted by the SCEV expander for certain kinds of
-        // pointer arithmetic.
-        if (match(V, m_Neg(m_PtrToInt(m_Value())))) {
-          Operator *Index = cast<Operator>(V);
-          Value *PtrToInt = Builder.CreatePtrToInt(PtrOp, Index->getType());
-          Value *NewSub = Builder.CreateSub(PtrToInt, Index->getOperand(1));
-          return CastInst::Create(Instruction::IntToPtr, NewSub, GEPType);
-        }
         // Canonicalize (gep i8* X, (ptrtoint Y)-(ptrtoint X))
         // to (bitcast Y)
         Value *Y;
         if (match(V, m_Sub(m_PtrToInt(m_Value(Y)),
                            m_PtrToInt(m_Specific(GEP.getOperand(0))))))
           return CastInst::CreatePointerBitCastOrAddrSpaceCast(Y, GEPType);
       }
     }

llvm/test/Transforms/InstCombine/getelementptr.ll

;
   %ret = ptrtoint i8 addrspace(1)* %gep2 to i16
   ret i16 %ret
 
 }
 
 define i8* @test42(i8* %c1, i8* %c2) {
 ; CHECK-LABEL: @test42(
 ; CHECK-NEXT:    [[PTRTOINT:%.*]] = ptrtoint i8* [[C1:%.*]] to i64
-; CHECK-NEXT:    [[TMP1:%.*]] = ptrtoint i8* [[C2:%.*]] to i64
-; CHECK-NEXT:    [[TMP2:%.*]] = sub i64 [[TMP1]], [[PTRTOINT]]
-; CHECK-NEXT:    [[GEP:%.*]] = inttoptr i64 [[TMP2]] to i8*
+; CHECK-NEXT:    [[SUB:%.*]] = sub i64 0, [[PTRTOINT]]
+; CHECK-NEXT:    [[GEP:%.*]] = getelementptr inbounds i8, i8* [[C2:%.*]], i64 [[SUB]]
 ; CHECK-NEXT:    ret i8* [[GEP]]
 ;
   %ptrtoint = ptrtoint i8* %c1 to i64
   %sub = sub i64 0, %ptrtoint
   %gep = getelementptr inbounds i8, i8* %c2, i64 %sub
   ret i8* %gep
 
 }
 
 define i16* @test43(i16* %c1, i16* %c2) {
 ; CHECK-LABEL: @test43(
 ; CHECK-NEXT:    [[PTRTOINT:%.*]] = ptrtoint i16* [[C1:%.*]] to i64
-; CHECK-NEXT:    [[TMP1:%.*]] = ptrtoint i16* [[C2:%.*]] to i64
-; CHECK-NEXT:    [[TMP2:%.*]] = sub i64 [[TMP1]], [[PTRTOINT]]
-; CHECK-NEXT:    [[GEP:%.*]] = inttoptr i64 [[TMP2]] to i16*
+; CHECK-NEXT:    [[SUB:%.*]] = sub i64 0, [[PTRTOINT]]
+; CHECK-NEXT:    [[SHR:%.*]] = ashr i64 [[SUB]], 1
+; CHECK-NEXT:    [[GEP:%.*]] = getelementptr inbounds i16, i16* [[C2:%.*]], i64 [[SHR]]
 ; CHECK-NEXT:    ret i16* [[GEP]]
 ;
   %ptrtoint = ptrtoint i16* %c1 to i64
   %sub = sub i64 0, %ptrtoint
   %shr = ashr i64 %sub, 1
   %gep = getelementptr inbounds i16, i16* %c2, i64 %shr
   ret i16* %gep
 
 }
 
 define %struct.C* @test44(%struct.C* %c1, %struct.C* %c2) {
 ; CHECK-LABEL: @test44(
 ; CHECK-NEXT:    [[PTRTOINT:%.*]] = ptrtoint %struct.C* [[C1:%.*]] to i64
-; CHECK-NEXT:    [[TMP1:%.*]] = ptrtoint %struct.C* [[C2:%.*]] to i64
-; CHECK-NEXT:    [[TMP2:%.*]] = sub i64 [[TMP1]], [[PTRTOINT]]
-; CHECK-NEXT:    [[GEP:%.*]] = inttoptr i64 [[TMP2]] to %struct.C*
+; CHECK-NEXT:    [[SUB:%.*]] = sub i64 0, [[PTRTOINT]]
+; CHECK-NEXT:    [[SHR:%.*]] = sdiv i64 [[SUB]], 7
+; CHECK-NEXT:    [[GEP:%.*]] = getelementptr inbounds [[STRUCT_C:%.*]], %struct.C* [[C2:%.*]], i64 [[SHR]]
 ; CHECK-NEXT:    ret %struct.C* [[GEP]]
 ;
   %ptrtoint = ptrtoint %struct.C* %c1 to i64
   %sub = sub i64 0, %ptrtoint
   %shr = sdiv i64 %sub, 7
   %gep = getelementptr inbounds %struct.C, %struct.C* %c2, i64 %shr
   ret %struct.C* %gep