[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
----------------
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.


Repository:
  rG LLVM Github Monorepo

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

https://reviews.llvm.org/D152963