[LLVMdev] where does %a_addr.0 come from?

[maarten faddegon]

Hi,

I am studying SSA and some time ago I asked on this list how to see the
phi nodes in the llvm ir output. I learned then to use this command:
opt -mem2reg test.ll -S > test_mem2reg.ll

However, if you look at the output (attached to this message) there is
something I do not understand. At the end of the function @f at line 18,
the function returns the variable %a_addr.0. However, this variable is
never defined or set. The variable %a is. Is "_addr.0"  a way to get the
address of a variable? I could not find anything about this in in LLVM
language reference manual.
Where does this variable come from?


thanks,
  Maarten Faddegon
-------------- next part --------------
; ModuleID = 'test.ll'
target datalayout = "e-p:64:64:64-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:64:64-f32:32:32-f64:64:64-v64:64:64-v128:128:128-a0:0:64-s0:64:64-f80:128:128-n8:16:32:64"
target triple = "x86_64-unknown-linux-gnu"

define i32 @f(i32 %a) nounwind {
entry:
  %"alloca point" = bitcast i32 0 to i32          ; <i32> [#uses=0]
  %0 = sub nsw i32 %a, 5                          ; <i32> [#uses=1]
  %1 = icmp sgt i32 %0, 10                        ; <i1> [#uses=1]
  br i1 %1, label %bb, label %bb1

bb:                                               ; preds = %entry
  br label %bb2

bb1:                                              ; preds = %entry
  br label %bb2

bb2:                                              ; preds = %bb1, %bb
  %a_addr.0 = phi i32 [ 1, %bb ], [ 0, %bb1 ]     ; <i32> [#uses=1]
  br label %return

return:                                           ; preds = %bb2
  ret i32 %a_addr.0
}

define i32 @main(i32 %argc, i8** %argv) nounwind {
entry:
  %"alloca point" = bitcast i32 0 to i32          ; <i32> [#uses=0]
  %0 = call i32 @f(i32 %argc) nounwind            ; <i32> [#uses=1]
  br label %return

return:                                           ; preds = %entry
  ret i32 %0
}