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How can I find the virtual register number associated with variable x in this scenario? I can identify the annotated variable using a function pass and want to find virtual register number next.
Is a machine function pass the way to proceed? 

#include <stdio.h>

int main (){
int x __attribute__((annotate("my_var")))= 0;
int a,b;
x = x + 1;
a = 5;
b = 6;
x = x + a;

return x;
}

Generated IR

; ModuleID = 'test.c'
source_filename = "test.c"
target datalayout = "e-m:e-i8:8:32-i16:16:32-i64:64-i128:128-n32:64-S128"
target triple = "aarch64"

@.str = private unnamed_addr constant [7 x i8] c"my_var\00", section "llvm.metadata"
@.str.1 = private unnamed_addr constant [7 x i8] c"test.c\00", section "llvm.metadata"

; Function Attrs: noinline nounwind optnone
define i32 @main() #0 {
  %1 = alloca i32, align 4
  %2 = alloca i32, align 4
  %3 = alloca i32, align 4
  %4 = alloca i32, align 4
  store i32 0, i32* %1, align 4
  %5 = bitcast i32* %2 to i8*
  call void @llvm.var.annotation(i8* %5, i8* getelementptr inbounds ([7 x i8], [7 x i8]* @.s$
  store i32 0, i32* %2, align 4
  %6 = load i32, i32* %2, align 4
  %7 = add nsw i32 %6, 1
  store i32 %7, i32* %2, align 4
  store i32 5, i32* %3, align 4
  store i32 6, i32* %4, align 4
  %8 = load i32, i32* %2, align 4
  %9 = load i32, i32* %3, align 4
  %10 = add nsw i32 %8, %9
  store i32 %10, i32* %2, align 4
  %11 = load i32, i32* %2, align 4
  ret i32 %11
}

; Function Attrs: nounwind
declare void @llvm.var.annotation(i8*, i8*, i8*, i32) #1

attributes #0 = { noinline nounwind optnone "correctly-rounded-divide-sqrt-fp-math"="false" $
attributes #1 = { nounwind }

!llvm.module.flags = !{!0}
!llvm.ident = !{!1}
!0 = !{i32 1, !"wchar_size", i32 4}
Improve this question
2
  • First of all, I'd suggest compiling your program with debug information. Commented Sep 26, 2017 at 8:56
  • This answer may be helpful: stackoverflow.com/a/21411476 The question asks about the inverse mapping, but I guess you can apply the information as well. Commented Sep 26, 2017 at 9:01
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