[llvm-dev] Register classes and FP64 on target with no FP64 support

Martin J. O'Riordan via llvm-dev llvm-dev at lists.llvm.org
Thu Sep 29 03:39:06 PDT 2016

Hi LLVM-Dev,


I am trying to implement support for emulated FP64 on our target.  Many
operations work fine, invoking the appropriate helper function in
'compiler-rt'.  But we don't have a specific register class for FP64 and
LLVM usually selects a pair of 32-bit integers, which is fine.  The problem
is that it doesn't "always" select a pair of 32-bit integers, and then I get
an assertion in 'TargetRegisterInfo::getMinimalPhysRegClass' that says
"Couldn't find the register class".


The funny thing is that something like 'a = b * c;' works perfectly, but the
much simple 'a = b;' causes this assertion.


We have not used 'setOperationAction' for any of the FP64 operations, nor
have we created a special register class for them either, in the expectation
that it would just reduce to the underlying integers and 'compiler-rt'


I'm a bit stumped, so does anyone have any advice about how I should
describe our target so that it supports emulated FP64 using either a pair of
32-bit integers or a single 64-bit register as the underlying implementation




            MartinO - Movidius


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