[LLVMdev] Load/Store issues: tablegen/customization?

Daniel M Gessel gessel at apple.com
Mon Nov 10 13:20:03 PST 2008

I've been running into two issues with load/store handling:

(1) is that tablegen doesn't seem to handle the two predicates that  
get attached to my instructions. The first is the predicate in  
TargetSelectionDAG.td, identifying a load node as, say, extloadi8. The  
second is my identification of the load as having a particular address  
space (need different instructions for different address spaces).

In the tablegen generated code, only one predicate is tested. Anybody  
seen anything similar to this (i.e. is this a known issue)? Do people  
have experience with multiple predicates working just fine?

I've been directly matching "ld" and been testing in a world that only  
does 32 bit aligned loads and things have "just worked", but I've got  
my sights set higher now (load of bytes, store of 4 x byte vectors,  

(2) The HW I'm targeting does not have byte/short load/store; the  
finest granularity is aligned 32 bit load/store (like the original  
Alpha architecture). In addition, I want to optimize certain vector  
operations (128 bit load/store) and some are getting converted from 32  
bit to multiple 8 bit operations (e.g. store a 4 element vector of  
chars becomes 4 one byte stores), but I don't want to provide full  
vector register support (at this time).

Any hints on a good approach to dealing with the 32 bit aligned load/ 
store limitations and mixing and matching "native" load/store support  
of vector types with LLVM generated expansions of vector operations?



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