[LLVMdev] SSA?

[dan mihai]

Hello,

I am a bit confused about the nature of LLVM's SSA and IR in general.
Questions:

1) Is it possible to get LLVM to generate code as in /*2*/ (bellow)?

2) if not, how can I tell if an operand has been previously defined?


Here is why:
I thought (wrongly) that all operands of an instruction must have been 
previously defined or some constants.
I see that the 'bitcast' instruction is certainly standalone in certain cases, such as
    %[65]"alloca point" = bitcast i32 [34]0 to i32; <i32> [#uses=0]

However the following instruction has a 'bitcast' inserted as an operand, 
rather then the result of a previous bitcast:
/*1*/
    (void)store i32 (...)* bitcast (i32 ()* @pf to i32 (...)*), i32 (...)** @[2]pf0, align 8

In this case, the bitcast is a constant, but it does DEFINE a new value 
and that value is the operand. I would have thought that the above code 
should have been "pure IR/SSA":
/*2*/
    %TMP = bitcast (i32 ()* @pf to i32 (...)*)

    (void)store i32 (...)* %TMP, i32 (...)** @[2]pf0, align 8

or something like that...

Thank you,
Dan

 		 	   		  
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