[PATCH] D152963: [RISCV] Don't assume tail undefined if there's no policy op

[Luke Lau via Phabricator via llvm-commits]

luke added inline comments.


================
Comment at: llvm/test/CodeGen/RISCV/rvv/rvv-peephole-vmerge-vops.ll:475
 ; CHECK:       # %bb.0:
-; CHECK-NEXT:    vsetvli zero, a0, e32, m1, ta, ma
+; CHECK-NEXT:    vsetvli zero, a0, e32, m1, tu, ma
 ; CHECK-NEXT:    vadd.vv v8, v9, v10
----------------
luke wrote:
> craig.topper wrote:
> > Was something other than compares affected that changed this test?
> Yeah, this changes the interaction with the vmerge fold combine. The combine turns this DAG:
> 
> ```
> t27: nxv2i32 = PseudoVADD_VV_M1_MASK IMPLICIT_DEF:nxv2i32, t4, t6, Register:nxv2i1 $v0, t8, TargetConstant:i64<5>, TargetConstant:i64<1>, t35:1
>   t4: nxv2i32,ch = CopyFromReg t0, Register:nxv2i32 %1
>     t0: ch,glue = EntryToken
>   t6: nxv2i32,ch = CopyFromReg t0, Register:nxv2i32 %2
>   t8: i64,ch = CopyFromReg t0, Register:i64 %3
>   t35: ch,glue = CopyToReg t0, Register:nxv2i1 $v0, t30
>     t30: nxv2i1 = PseudoVMSET_M_B2 TargetConstant:i64<-1>, TargetConstant:i64<0>
> ```
> 
> Into this:
> 
> ```
> t39: nxv2i32 = PseudoVADD_VV_M1_MASK t2, t4, t6, Register:nxv2i1 $v0, t8, TargetConstant:i64<5>, TargetConstant:i64<0>, t33:1
>   t2: nxv2i32,ch = CopyFromReg t0, Register:nxv2i32 %0
>     t0: ch,glue = EntryToken
>   t4: nxv2i32,ch = CopyFromReg t0, Register:nxv2i32 %1
>   t6: nxv2i32,ch = CopyFromReg t0, Register:nxv2i32 %2
>   t8: i64,ch = CopyFromReg t0, Register:i64 %3
>   t33: ch,glue = CopyToReg t0, Register:nxv2i1 $v0, t30
>     t30: nxv2i1 = PseudoVMSET_M_B2 TargetConstant:i64<-1>, TargetConstant:i64<0>
> ```
> 
> I.e. the merge operand in PseudoVADD_VV_M1_MASK is now set to something that isn't implicit_def.
> But previously doPeepholeMaskedRVV would have converted this into a tail undefined `PseudoVADD_VV_M1` anyway, even though we need to preserve the merge operand.  The tail undefined then got translated into a ta policy.
*turns this node:


Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D152963/new/

https://reviews.llvm.org/D152963