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Since https://github.com/ARM-software/acle/pull/276 the ACLE defines attributes to better describe the use of a given SME state. Previously the attributes merely described the possibility of it being 'shared' or 'preserved', whereas the new attributes have more semantics and also describe how the data flows through the program. For ZT0 we already had to add new LLVM IR attributes: * aarch64_new_zt0 * aarch64_in_zt0 * aarch64_out_zt0 * aarch64_inout_zt0 * aarch64_preserves_zt0 We have now done the same for ZA, such that we add: * aarch64_new_za (previously `aarch64_pstate_za_new`) * aarch64_in_za (more specific variation of `aarch64_pstate_za_shared`) * aarch64_out_za (more specific variation of `aarch64_pstate_za_shared`) * aarch64_inout_za (more specific variation of `aarch64_pstate_za_shared`) * aarch64_preserves_za (previously `aarch64_pstate_za_shared, aarch64_pstate_za_preserved`) This explicitly removes 'pstate' from the name, because with SME2 and the new ACLE attributes there is a difference between "sharing ZA" (sharing the ZA matrix register with the caller) and "sharing PSTATE.ZA" (sharing either the ZA or ZT0 register, both part of PSTATE.ZA with the caller).
IRgen optimization opportunities. //===---------------------------------------------------------------------===// The common pattern of -- short x; // or char, etc (x == 10) -- generates an zext/sext of x which can easily be avoided. //===---------------------------------------------------------------------===// Bitfields accesses can be shifted to simplify masking and sign extension. For example, if the bitfield width is 8 and it is appropriately aligned then is is a lot shorter to just load the char directly. //===---------------------------------------------------------------------===// It may be worth avoiding creation of alloca's for formal arguments for the common situation where the argument is never written to or has its address taken. The idea would be to begin generating code by using the argument directly and if its address is taken or it is stored to then generate the alloca and patch up the existing code. In theory, the same optimization could be a win for block local variables as long as the declaration dominates all statements in the block. NOTE: The main case we care about this for is for -O0 -g compile time performance, and in that scenario we will need to emit the alloca anyway currently to emit proper debug info. So this is blocked by being able to emit debug information which refers to an LLVM temporary, not an alloca. //===---------------------------------------------------------------------===// We should try and avoid generating basic blocks which only contain jumps. At -O0, this penalizes us all the way from IRgen (malloc & instruction overhead), all the way down through code generation and assembly time. On 176.gcc:expr.ll, it looks like over 12% of basic blocks are just direct branches! //===---------------------------------------------------------------------===//