[llvm-dev] getMinimalPhysRegClass : Couldn't find the register class

[Krzysztof Parzyszek via llvm-dev]

Could you post the output from -debug-only=isel?

The transformed IR works for me.

-Krzysztof

On 11/9/2016 12:58 PM, Peeter Joot via llvm-dev wrote:
> I've implemented a function pass, and some associated hacks to llvm and
> clang, and am hitting an error in a DAG pass when my transformed IR is
> processed.  That transformed bytecode attempts to insert a call around a
> load of a 'long double'.  The error is:
>
>     3.      Running pass 'Function Pass Manager' on module 'big.c'.
>
>     4.      Running pass 'X86 DAG->DAG Instruction Selection' on
> function '@ld'
>
> The assert is after a failure to lookup a BestRC pointer in this function:
>
>
>
>     (gdb) b 141 if (BestRC == 0)
>
>     Breakpoint 3 at 0x7ffff6755436: file
> /home/pjoot/llvm/lib/CodeGen/TargetRegisterInfo.cpp, line 141.
>
>     (gdb) c
>
>     Continuing.
>
>     Breakpoint 3, llvm::TargetRegisterInfo::getMinimalPhysRegClass
> (this=0x5cc4f8, reg=44, VT=...) at
> /home/pjoot/llvm/lib/CodeGen/TargetRegisterInfo.cpp:141
>
>     141       assert(BestRC && "Couldn't find the register class");
>
>     (gdb) p reg
>
>     $4 = 44
>
>     (gdb) p c
>
>     $5 = (const llvm::TargetRegisterClass *) 0x0
>
>     (gdb) p VT
>
>     $6 = {SimpleTy = llvm::MVT::SimpleValueType::i32}
>
>
> The bytecode that my pass is producing is:
>
>     ; Function Attrs: nounwind uwtable
>
>     define x86_fp80 @ld(x86_fp80* nocapture readonly %d)
> local_unnamed_addr #0 {
>
>     entry:
>
>       %0 = load x86_fp80, x86_fp80* %d, align 16, !tbaa !1
>
>       %swap16 = tail call x86_fp80 @__lz_bswapld(x86_fp80 %0) #1
>
>       ret x86_fp80 %swap16
>
>     }
>
> where the untransformed bytecode was:
>
>     define x86_fp80 @ld(x86_fp80* nocapture readonly %d)
> local_unnamed_addr #0 {
>
>     entry:
>
>       %0 = load x86_fp80, x86_fp80* %d, align 16, !tbaa !1
>
>       ret x86_fp80 %0
>
>     }
>
> What about this transformed bytecode does the later DAG->DAG pass
> dislike?  What is the valid range of registers in this function (i.e. is
> the reg=45 value that I see in this function valid)?
>
> --
> Peeter
>
>
>
>
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