[LLVMdev] Extraction of Arguments Passed to a Function

Prabhat Kumar Saraswat prabhat.saraswat at gmail.com
Fri Jan 4 05:10:20 PST 2008

 I am trying to extract the name of the variables passed as an Argument to a
Function. I am using a runOnFunction Pass.
For example  in the following IR respresentation,

define void @foo(i32 %limit) {

I should be able to walk the IR and get '%limit' as the external variable
passed to the function.

Another question, Is it possible to create a basic symbol table ( internal
variables in a function, global variables outside of a fucntion ) only from
the entry: basic block.
According to my observation, it seems that the temporary variables created
for different basic block are independent from each other, for example in
the following IR the temp variables used in the basic block bb: i.e. %tmp,
%tmp1, %tmp2 are only dependent on the variables defined in the entry: basic
block, and same holds for basic block bb5: i.e. variables %tmp6, %tmp7,
%tmp8 etc are only dependent on the variables in the entry block
(%limit_addr, %i.. etc) and the temp variables defined in the same basic

Is this true ?, as far as i have seen, by generating the bitcode for various
test codes, and it holds true for all. So, now the proposition is, that one
can create the symbol table of the internal variables and the variables
passed to the function as an agrument by only using the information in entry
block and argument list information.

The IR....
define void @foo(i32 %limit) {
    %limit_addr = alloca i32        ; <i32*> [#uses=2]
    %i = alloca i32, align 4        ; <i32*> [#uses=6]
    %"alloca point" = bitcast i32 0 to i32        ; <i32> [#uses=0]
    store i32 %limit, i32* %limit_addr
    store i32 0, i32* %i, align 4
    store i32 0, i32* %i, align 4
    br label %bb5

bb:        ; preds = %bb5
    %tmp = getelementptr [24 x i8]* @.str, i32 0, i32 0        ; <i8*>
    %tmp1 = load i32* %i, align 4        ; <i32> [#uses=1]
    %tmp2 = call i32 (i8* noalias , ...)* @printf( i8* %tmp noalias , i32
%tmp1 )        ; <i32> [#uses=0]
    %tmp3 = load i32* %i, align 4        ; <i32> [#uses=1]
    %tmp4 = add i32 %tmp3, 1        ; <i32> [#uses=1]
    store i32 %tmp4, i32* %i, align 4
    br label %bb5

bb5:        ; preds = %bb, %entry
    %tmp6 = load i32* @glob_var, align 4        ; <i32> [#uses=1]
    %tmp7 = load i32* %limit_addr, align 4        ; <i32> [#uses=1]
    %tmp8 = add i32 %tmp7, %tmp6        ; <i32> [#uses=1]
    %tmp9 = load i32* %i, align 4        ; <i32> [#uses=1]
    %tmp10 = icmp sge i32 %tmp8, %tmp9        ; <i1> [#uses=1]
    %tmp1011 = zext i1 %tmp10 to i8        ; <i8> [#uses=1]
    %toBool = icmp ne i8 %tmp1011, 0        ; <i1> [#uses=1]
    br i1 %toBool, label %bb, label %bb12

bb12:        ; preds = %bb5
    br label %return

return:        ; preds = %bb12
    ret void

Thanks and Regards
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