[LLVMdev] Why clang inlines with -O3 flag and opt doesn't?

[Yuri]

When I compile my C fibonacci example fib.c with 'clang -O3 -c -emit-llvm -o fib-clang.bc fib.c&&  llvm-dis fib-clang.bc' I get fib-clang.ll that has some degree of inlining in it.

But when I get an equivalent to fib.c file fib.ll and run it through opt with the command 'llvm-as fib.ll&&  opt -O3 fib.bc -o fib-opt.bc&&  llvm-dis fib-opt.bc' resulting fib-opt.ll doesn't have any degree of inlining despite the flag -O3.

Why clang with the flag -O3 inlines code and opt with the same -O3 doesn't?
How can I make opt inline my .ll code the same way?

Yuri

--- fiobonacci fib.c example ---
#include<stdlib.h>
#include<stdio.h>

int fib(int AnArg) {
  if (AnArg<= 2) return (1);
  return (fib(AnArg-1)+fib(AnArg-2));
}

int main(int argc, char* argv[]) {
  int n = atoi(argv[1]);
  printf("fib(%i)=%i\n", n, fib(n));
}


--- my handcrafted fib.ll ---
define i32 @fib(i32) nounwind readnone {
fib.top:
   %xcmp1 = icmp ugt i32 %0, 1
   br i1 %xcmp1, label %maj, label %spec

maj:
   %m1 = add i32 %0, -1
   %1 = tail call i32 @fib(i32 %m1)
   %m2 = add i32 %0, -2
   %2 = tail call i32 @fib(i32 %m2)
   %res = add i32 %2, %1
   ret i32 %res

spec:
   %xcmp = icmp eq i32 %0, 1
   %mres = zext i1 %xcmp to i32
   ret i32 %mres
}

@.str = private constant [12 x i8] c"fib(%i)=%i\0A\00" ;<[12 x i8]*>  [#uses=1]

define i32 @main(i32 %argc, i8** nocapture %argv) nounwind {
entry:
   %arrayidx = getelementptr inbounds i8** %argv, i64 1 ;<i8**>  [#uses=1]
   %tmp1 = load i8** %arrayidx, align 8            ;<i8*>  [#uses=1]
   %call = tail call i32 @atoi(i8* %tmp1) nounwind ;<i32>  [#uses=2]
   %call4 = tail call i32 @fib(i32 %call)          ;<i32>  [#uses=1]
   %call5 = tail call i32 (i8*, ...)* @printf(i8* getelementptr inbounds ([12 x i8]* @.str, i64 0, i64 0), i32 %call, i32 %call4) nounwind ;<i32>  [#uses=0]
   ret i32 0
}

declare i32 @atoi(i8* nocapture) nounwind readonly

declare i32 @printf(i8* nocapture, ...) nounwind