I have the following llvm ir and having spent the best part of the day trying to debug it I cannot seem to get a handle on it. The program simply freezes (with) segfault at the loop when run on my windows machine.
; standard declaration etc
%gen__list__0 = type { i8*, i64, i64 }
%const_array_offset = type { i64, i64 }
; other declaration etc
@gbl_constant_59 = common constant [20 x i8] c"aaaaaaaaaaaaaaaaaaaa", align
; more function declarations etc
define internal %gen__list__0 @gen__fun__elevate12(%const_array_offset*) {
entry:
%1 = alloca %gen__list__0
%2 = getelementptr %const_array_offset, %const_array_offset* %0, i32 0, i32 0
%3 = load i64, i64* %2
%4 = getelementptr %const_array_offset, %const_array_offset* %0, i32 0, i32 1
%5 = load i64, i64* %4
%6 = sub i64 %5, %3
%7 = mul i64 %6, i64 2
%8 = getelementptr %gen__list__0, %gen__list__0* %1, i32 0, i32 0
%9 = getelementptr %gen__list__0, %gen__list__0* %1, i32 0, i32 1
%10 = getelementptr %gen__list__0, %gen__list__0* %1, i32 0, i32 2
store i64 %6, i64* %9
store i64 %7, i64* %10
%11 = mul i64 ptrtoint (i8* getelementptr (i8, i8* null, i32 1) to i64), %7
%12 = call i8* @malloc(i64 %11)
store i8* %12, i8** %8
%13 = getelementptr %gen__list__0, %gen__list__0* %1, i32 0, i32 0
%14 = load i8*, i8** %13
%15 = getelementptr i8, i8* %14, i64 %6
%16 = getelementptr [20 x i8], [20 x i8]* @gbl_constant_59, i32 0, i64 %3
%17 = alloca i8*
store i8* %16, i8** %17
%18 = alloca i8*
store i8* %14, i8** %18
br label %bb2
bb2: ; preds = %bb3, %entry
%19 = load i8*, i8** %18
%20 = icmp ne i8* %19, %15
br i1 %20, label %bb3, label %bb4
bb3: ; preds = %bb2
%21 = load i8*, i8** %17
%22 = getelementptr i8, i8* %21, i32 1
store i8* %22, i8** %17
%23 = load i8*, i8** %18
%24 = getelementptr i8, i8* %23, i32 1
store i8* %24, i8** %18
br label %bb2
bb4: ; preds = %bb2
%25 = load %gen__list__0, %gen__list__0* %1
ret %gen__list__0 %25
}
All help appreciated to straighten this out/where it/I may be going wrong.
The loop simply implements
c++ style psuedo code for the sort of loop this implements
for(iterator it = begin; it != end; ++it) {
//code in loop - atm blank
}
The problem was found by putting the code through llc. Apparently constants marked with common linkage can only have a zero initializer. To have a global constant without a zero initializer, as in the case of @gbl_constant_59 here, you need to declare the constant internal or external.