[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:7986
+  Align Alignment = cast<ConstantPoolSDNode>(CPIdx)->getAlign();
+  SDValue Load = DAG.getLoad(
+      VT, dl, DAG.getEntryNode(),
----------------
gsocshubham wrote:
> craig.topper wrote:
> > gsocshubham wrote:
> > > 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.
> > A zext load with i8 memVT?
> Zext eith memVt without checking VT type legality for `llvm.cttz.i32(i32 %x, i1 true)` compiled with SPARC gives -
> 
> ```
> f:                                      ! @f
>         .cfi_startproc
> ! %bb.0:                                ! %entry
>         mov     %o0, %o1
>         cmp %o0, 0
>         be      .LBB0_2
>         mov     %g0, %o0
> ! %bb.1:                                ! %entry
>         sub %o0, %o1, %o0
>         and %o1, %o0, %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
>         ld [%o1+%o0], %o0
> 
> ```
> Zext eith memVt without checking VT type legality for `llvm.cttz.i32(i32 %x, i1 true)` compiled with SPARC gives -
> 
> ```
> f:                                      ! @f
>         .cfi_startproc
> ! %bb.0:                                ! %entry
>         mov     %o0, %o1
>         cmp %o0, 0
>         be      .LBB0_2
>         mov     %g0, %o0
> ! %bb.1:                                ! %entry
>         sub %o0, %o1, %o0
>         and %o1, %o0, %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
>         ld [%o1+%o0], %o0
> 
> ```

ZExt with MemVT


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

https://reviews.llvm.org/D128911