[PATCH] D128911: Emit table lookup from TargetLowering::expandCTTZ()

[Shubham Narlawar via Phabricator via llvm-commits]

gsocshubham added inline comments.


================
Comment at: llvm/lib/CodeGen/SelectionDAG/TargetLowering.cpp:7984
+      CA, getPointerTy(TD),
+      TD.getPrefTypeAlign(VT.getTypeForEVT(*DAG.getContext())));
+  Align Alignment = cast<ConstantPoolSDNode>(CPIdx)->getAlign();
----------------
craig.topper wrote:
> Replace VT.getTypeForEVT(*DAG.getContext()) with `CA->getType()`
If I change alignment as above, then for `call i32 @llvm.cttz.i32(i32 %x, i1 true)` compiled with SPARC -

I get -

```
f:                                      ! @f
        .cfi_startproc
! %bb.0:                                ! %entry
        mov     %g0, %o1
        sub %o1, %o0, %o1
        and %o0, %o1, %o0
        sethi 122669, %o1
        or %o1, 305, %o1
        smul %o0, %o1, %o0
        srl %o0, 27, %o0
        sethi %hi(.LCPI0_0), %o1
        add %o1, %lo(.LCPI0_0), %o1
        add %o1, %o0, %o2
        ldub [%o2+2], %o3
        ldub [%o2+3], %o4
        ldub [%o1+%o0], %o0
        ldub [%o2+1], %o1
        sll %o3, 8, %o2
        or %o2, %o4, %o2
        sll %o0, 8, %o0
        or %o0, %o1, %o0
        sll %o0, 16, %o0
        retl
        or %o0, %o2, %o0
```

instead of -

```
        mov     %g0, %o1
        sub %o1, %o0, %o1
        and %o0, %o1, %o0
        sethi 122669, %o1
        or %o1, 305, %o1
        smul %o0, %o1, %o0
        srl %o0, 27, %o0
        sethi %hi(.LCPI0_0), %o1
        add %o1, %lo(.LCPI0_0), %o1
        retl
        ld [%o1+%o0], %o0

```


================
Comment at: llvm/lib/CodeGen/SelectionDAG/TargetLowering.cpp:7986
+  Align Alignment = cast<ConstantPoolSDNode>(CPIdx)->getAlign();
+  SDValue Load = DAG.getLoad(
+      VT, dl, DAG.getEntryNode(),
----------------
craig.topper wrote:
> What happens if you always create a zextload even if the type isn't legal?
There is no change in generated code nor in LIT test failures as it was originally submitted earlier.


CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D128911/new/

https://reviews.llvm.org/D128911