[PowerPC] Improve code gen for vector add

[lei]

Summary

Improve codegen for vectors modulo additions.

[lei]

Patch by Nemanja

[stefanp]

I think that this patch is fine but I think there may be something missing in terms of vaddudm . Currently a test case like this one:

define dso_local <2 x i64> @x2d(<2 x i64> noundef %x) {
entry:
  %add = shl <2 x i64> %x, <i64 1, i64 1>
  ret <2 x i64> %add
}

Produces some fairly inefficient code:

x2d:                                    # @x2d
.Lfunc_begin3:
        .cfi_startproc
.Lfunc_gep3:
        addis 2, 12, .TOC.-.Lfunc_gep3@ha
        addi 2, 2, .TOC.-.Lfunc_gep3@l
.Lfunc_lep3:
        .localentry     x2d, .Lfunc_lep3-.Lfunc_gep3
# %bb.0:                                # %entry
        addis 3, 2, .LCPI3_0@toc@ha
        addi 3, 3, .LCPI3_0@toc@l
        lxv 35, 0(3)
        vsld 2, 2, 3
        blr

We even do a TOC access.

Unfortunately, this isn't just a case of adding:

def : Pat<(v2i64 (shl v2i64:$vA, (v2i64 (immEQOneV)))),
          (v2i64 (VADDUDM $vA, $vA))>;

like the others but I think it may be worth doing.

At this point maybe just add the test case and we can deal with the issue at a later date.

[nemanjai]

In D154447#4472054, @stefanp wrote:

Unfortunately, this isn't just a case of adding:

def : Pat<(v2i64 (shl v2i64:$vA, (v2i64 (immEQOneV)))),
          (v2i64 (VADDUDM $vA, $vA))>;

like the others but I think it may be worth doing.

Yeah, this is because we don't have a way of materializing the <1, 1> vector so we end up with a constant pool load. We can provide custom legalization:
setOperationAction(ISD::SHL, MVT::v2i64, Custom); for Power8 and up where we would just leave the node alone if it's a shift by 1.

At this point maybe just add the test case and we can deal with the issue at a later date.

I agree this can be done in a follow-up patch.

[lei]

add new tc and update to test for pwr8 since we are more interested
in the new tc behaviour for pwr8 and orig tc is same for pwr8 vs pwr7.

[nemanjai]

LGTM.

llvm/lib/Target/PowerPC/PPCInstrAltivec.td

def : Pat<(v16i8 (sra (sub v16i8:$vA, (v16i8 (bitconvert(vnot v4i32:$vB)))),
           (v16i8 (immEQOneV)))), (v16i8 (VAVGSB $vA, $vB))>;
 def : Pat<(v4i32 (srl (sub v4i32:$vA, (vnot v4i32:$vB)),
           (v4i32 (immEQOneV)))), (v4i32 (VAVGUW $vA, $vB))>;
 def : Pat<(v8i16 (srl (sub v8i16:$vA, (v8i16 (bitconvert(vnot v4i32:$vB)))),
           (v8i16 (immEQOneV)))), (v8i16 (VAVGUH $vA, $vB))>;
 def : Pat<(v16i8 (srl (sub v16i8:$vA, (v16i8 (bitconvert(vnot v4i32:$vB)))),
           (v16i8 (immEQOneV)))), (v16i8 (VAVGUB $vA, $vB))>;
 
+def : Pat<(v16i8 (shl v16i8:$vA, (v16i8 (immEQOneV)))),
+          (v16i8 (VADDUBM $vA, $vA))>;
+def : Pat<(v8i16 (shl v8i16:$vA, (v8i16 (immEQOneV)))),
+          (v8i16 (VADDUHM $vA, $vA))>;
+def : Pat<(v4i32 (shl v4i32:$vA, (v4i32 (immEQOneV)))),
+          (v4i32 (VADDUWM $vA, $vA))>;
+
 } // end HasAltivec
 
 // [PO VRT VRA VRB 1 PS XO], "_o" means CR6 is set.
 class VX_VT5_VA5_VB5_PS1_XO9_o<bits<9> xo, string opc, list<dag> pattern>
   : VX_RD5_RSp5_PS1_XO9<xo,
                    (outs vrrc:$VD), (ins vrrc:$VA, vrrc:$VB, u1imm:$PS),
                    !strconcat(opc, " $VD, $VA, $VB, $PS"), IIC_VecFP, pattern> {
   let Defs = [CR6];

llvm/test/CodeGen/PowerPC/optimize-vector.ll

 ; NOTE: Assertions have been autogenerated by utils/update_llc_test_checks.py UTC_ARGS: --version 2
 ; RUN: llc -verify-machineinstrs -mtriple=powerpc64le-unknown-linux-gnu \
 ; RUN:   -mcpu=pwr7 -ppc-asm-full-reg-names -ppc-vsr-nums-as-vr < %s | \
 ; RUN:   FileCheck %s
 
 define dso_local <16 x i8> @x2(<16 x i8> noundef %x) {
 ; CHECK-LABEL: x2:
 ; CHECK:       # %bb.0: # %entry
-; CHECK-NEXT:    vspltisb v3, 1
-; CHECK-NEXT:    vslb v2, v2, v3
+; CHECK-NEXT:    vaddubm v2, v2, v2
 ; CHECK-NEXT:    blr
 entry:
   %add = shl <16 x i8> %x, <i8 1, i8 1, i8 1, i8 1, i8 1, i8 1, i8 1, i8 1, i8 1, i8 1, i8 1, i8 1, i8 1, i8 1, i8 1, i8 1>
   ret <16 x i8> %add
 }
 
 define dso_local <8 x i16> @x2h(<8 x i16> noundef %x) {
 ; CHECK-LABEL: x2h:
 ; CHECK:       # %bb.0: # %entry
-; CHECK-NEXT:    vspltish v3, 1
-; CHECK-NEXT:    vslh v2, v2, v3
+; CHECK-NEXT:    vadduhm v2, v2, v2
 ; CHECK-NEXT:    blr
 entry:
   %add = shl <8 x i16> %x, <i16 1, i16 1, i16 1, i16 1, i16 1, i16 1, i16 1, i16 1>
   ret <8 x i16> %add
 }
 
 define dso_local <4 x i32> @x2w(<4 x i32> noundef %x) {
 ; CHECK-LABEL: x2w:
 ; CHECK:       # %bb.0: # %entry
-; CHECK-NEXT:    vspltisw v3, 1
-; CHECK-NEXT:    vslw v2, v2, v3
+; CHECK-NEXT:    vadduwm v2, v2, v2
 ; CHECK-NEXT:    blr
 entry:
   %add = shl <4 x i32> %x, <i32 1, i32 1, i32 1, i32 1>
   ret <4 x i32> %add
 }