[PATCH] D54358: [AMDGPU] Disable DAG combine at -O0

[Stanislav Mekhanoshin via Phabricator via llvm-commits]

rampitec marked an inline comment as done.
rampitec added inline comments.


================
Comment at: lib/Target/AMDGPU/SIISelLowering.cpp:8704-8721
   case ISD::SCALAR_TO_VECTOR: {
     SelectionDAG &DAG = DCI.DAG;
     EVT VT = N->getValueType(0);
 
     // v2i16 (scalar_to_vector i16:x) -> v2i16 (bitcast (any_extend i16:x))
     if (VT == MVT::v2i16 || VT == MVT::v2f16) {
       SDLoc SL(N);
----------------
scott.linder wrote:
> The only regression I see is for something of the form:
> 
> ```
> target triple = "amdgcn-amd-amdhsa"
> 
> ; Function Attrs: noinline optnone
> define void @spam() #0 {
>   %tmp = load <3 x i16>, <3 x i16> addrspace(5)* undef, align 8
>   %tmp1 = insertelement <3 x i16> %tmp, i16 0, i64 0
>   store <3 x i16> %tmp1, <3 x i16> addrspace(5)* undef, align 8
>   ret void
> }
> 
> attributes #0 = { noinline optnone "target-cpu"="fiji" }
> ```
> 
> For which we produce:
> 
> ```
> Optimized legalized selection DAG: %bb.0 'spam:'
> SelectionDAG has 19 nodes:
>   t0: ch = EntryToken
>           t43: v2i16 = scalar_to_vector Constant:i16<0>
>         t57: i32 = bitcast t43
>       t68: ch = store<(store 2 into `<3 x i16> addrspace(5)* undef`, align 8, addrspace 5), trunc to i16> t40:1, t57, undef:i32, undef:i32
>               t41: v2i32 = BUILD_VECTOR t40, t40
>             t63: i64 = bitcast t41
>           t36: i64 = srl t63, Constant:i32<32>
>         t37: i16 = truncate t36
>       t21: ch = store<(store 2 into `<3 x i16> addrspace(5)* undef` + 4, align 4, addrspace 5)> t40:1, t37, undef:i32, undef:i32
>     t22: ch = TokenFactor t68, t21
>     t9: i64,ch = CopyFromReg t0, Register:i64 %0
>   t11: ch,glue = CopyToReg t22, Register:i64 $sgpr30_sgpr31, t9
>   t40: i32,ch = load<(load 4 from `<3 x i16> addrspace(5)* undef`, align 8, addrspace 5)> t0, undef:i32, undef:i32
>   t12: ch = RET_FLAG t11, Register:i64 $sgpr30_sgpr31, t11:1
> ```
> 
> And then fail to select `t43: v2i16 = scalar_to_vector Constant:i16<0>`
The fix for it here: D54718.


https://reviews.llvm.org/D54358