llvm dev - Sep 2015 - Upper 32bits from 64bit value

Hi,

I need to fetch lower and higher 32bits from 64bit value. I found
"CreateLShr" function to fetch lower 32bits,
llvm::Value *intermediateValue = LLVMIRBuilder->CreateLShr(x64BitValue, 32);

What function I need to use for fetching upper 32bits from 64bit value.

Thanks in advance,
Deep
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On 24 September 2015 at 22:12, Sandeep Kumar Singh via llvm-dev
<llvm-dev at lists.llvm.org> wrote:
> I need to fetch lower and higher 32bits from 64bit value. I found
> "CreateLShr" function to fetch lower 32bits,
> llvm::Value *intermediateValue = LLVMIRBuilder->CreateLShr(x64BitValue,
32);
That would give you the upper bits, I think.
> What function I need to use for fetching upper 32bits from 64bit value.
There's multiple ways to get the other half: "x & 0xffffffff"
is the
canonical one (LLVM's optimisers will convert the others into that if
they can).

Cheers.

Tim.

Hi Tim,

Thank you for reply.
> llvm::Value *intermediateValue = LLVMIRBuilder->CreateLShr(x64BitValue,
32);
Now I am using below to calculate upper 32bits, I think this is OK,
llvm::Value *intermediateValue = LLVMIRBuilder->CreateAnd(x64BitValue,
0xFFFFFFFF00000000);
intermediateValue = LLVMIRBuilder->CreateLShr(intermediateValue, 32);
    //cast value to 32 bit
    intermediateValue = castValueByOpSize(intermediateValue, 32);


Regards,
Deep

On Fri, Sep 25, 2015 at 7:12 PM, Tim Northover <t.p.northover at
gmail.com>
wrote:
> On 24 September 2015 at 22:12, Sandeep Kumar Singh via llvm-dev
> <llvm-dev at lists.llvm.org> wrote:
> > I need to fetch lower and higher 32bits from 64bit value. I found
> > "CreateLShr" function to fetch lower 32bits,
> > llvm::Value *intermediateValue =
LLVMIRBuilder->CreateLShr(x64BitValue,
> 32);
>
> That would give you the upper bits, I think.
>
> > What function I need to use for fetching upper 32bits from 64bit
value.
>
> There's multiple ways to get the other half: "x &
0xffffffff" is the
> canonical one (LLVM's optimisers will convert the others into that if
> they can).
>
> Cheers.
>
> Tim.
>


-- 

Thanks and Regards,
Sandeep Kumar Singh
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