[llvm-dev] BUILD_VECTOR disambiguation

[Craig Topper via llvm-dev]

Mixed types aren't allowed. They are checked for in VerifySDNode in
SelectionDAG.cpp and will fail an asserts build.

~Craig


On Tue, Jul 7, 2020 at 8:25 AM Krzysztof Parzyszek via llvm-dev <
llvm-dev at lists.llvm.org> wrote:

> The problem can happen when you want to build a vector of i8, but i8
> itself is not legal on your target.  All operands to BUILD_VECTOR will be
> legalized to the next legal integer type, so you can end up with a
> BUILD_VECTOR of vNi8 where all operands are i32, for example.
>
> Actual mixed types are less likely to happen, but if you are doing your
> own target-specific lowering, you can end up with mixed types, simply
> because your code doesn't have to make them all the same.
>
> --
> Krzysztof Parzyszek  kparzysz at quicinc.com   AI tools development
>
> > -----Original Message-----
> > From: Cameron McInally <cameron.mcinally at nyu.edu>
> > Sent: Tuesday, July 7, 2020 10:10 AM
> > To: Krzysztof Parzyszek <kparzysz at quicinc.com>
> > Cc: llvm-dev at lists.llvm.org
> > Subject: [EXT] Re: [llvm-dev] BUILD_VECTOR disambiguation
> >
> > Thanks for the clarification. The `except` seemed dangling to me, but
> it's
> > early here.
> >
> > Just curious... how do we end up with a mixed type BUILD_VECTOR?
> > That's counterintuitive.
> >
> > On Tue, Jul 7, 2020 at 10:58 AM Krzysztof Parzyszek via llvm-dev <llvm-
> > dev at lists.llvm.org> wrote:
> > >
> > > Mixed integer types are ok, but the values will get truncated to the
> > element type of the output value.  It's pretty much what the comment
> says.
> > >
> > > --
> > > Krzysztof Parzyszek  kparzysz at quicinc.com   AI tools development
> > >
> > > > -----Original Message-----
> > > > From: llvm-dev <llvm-dev-bounces at lists.llvm.org> On Behalf Of
> > > > Cameron McInally via llvm-dev
> > > > Sent: Tuesday, July 7, 2020 9:53 AM
> > > > To: LLVM Developers Mailing List <llvm-dev at lists.llvm.org>
> > > > Subject: [EXT] [llvm-dev] BUILD_VECTOR disambiguation
> > > >
> > > > Hey devs,
> > > >
> > > > From ISDOpcodes.h...
> > > >
> > > > /// BUILD_VECTOR(ELT0, ELT1, ELT2, ELT3,...) - Return a fixed-width
> > > > vector /// with the specified, possibly variable, elements. The
> > > > number of elements /// is required to be a power of two. The types
> > > > of the operands must all be /// the same and must match the vector
> > > > element type, except that integer types /// are allowed to be larger
> > > > than the element type, in which case the operands /// are implicitly
> > truncated.
> > > > BUILD_VECTOR,
> > > >
> > > > Must the operand types always be the same? Or could we see a
> > > > BUILD_VECTOR with mixed integer types? E.g.:
> > > >
> > > > BUILD_VECTOR(i32, i32, i64, i32)
> > > >
> > > > Thanks,
> > > > Cam
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