[PATCH] D108618: [CGCall] Add NoInline attr if presented for the target

[Djordje Todorovic via Phabricator via cfe-commits]

djtodoro added a comment.

In D108618#2964265 <https://reviews.llvm.org/D108618#2964265>, @rjmccall wrote:

> Why do you want to add `noinline` to a function declaration that lacks a definition?

If this won't be used at all I guess the compiler should throw a warning at least.
One example comes to my mind, and it includes LTO (and cross-compile unit inlining).

  $ cat test-1.c
  extern int __attribute__((noinline)) bar(void);
  
  int foo() {
  int v1 = bar();
  if (v1 > 100)
    return 0;
  v1--;
  return v1;
  }
  
  $ cat $ cat test-2.c
  int __attribute__((always_inline)) bar(void);
  
  int foo2() {
  int v2 = bar();   
  if (v2 > 1000)
    return 0;
  v2++;
  return v2;
  }
  
  $ cat test.c
  #include <stdio.h>
  
  extern int foo();
  extern int foo2();
  
  int bar() {
  int x;
  scanf("%d", &x);
  ++x;
  return x;
  }
  
  
  int main()
  {
  int i = foo();
  int j = foo2();
  return i - j;
  }
  
  $ clang test.c -g -S -flto -emit-llvm
  $ clang test-1.c -g -S -flto -emit-llvm
  $ clang test-2.c -g -S -flto -emit-llvm
  
  $ llvm-link -S -o linked.ll test-1.ll test-2.ll test.ll
  $ opt -S -O1 linked.ll -o optimized.ll

Having these simple compile units, I can expect that compiler is able to inline the `bar()` into `foo2()` but not into `foo()`.


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https://reviews.llvm.org/D108618