[llvm-bugs] [Bug 26115] New: [Inliner] Callee with single call instruction not being inlined

[via llvm-bugs]

https://llvm.org/bugs/show_bug.cgi?id=26115

            Bug ID: 26115
           Summary: [Inliner] Callee with single call instruction not
                    being inlined
           Product: libraries
           Version: trunk
          Hardware: PC
                OS: Windows NT
            Status: NEW
          Severity: normal
          Priority: P
         Component: Interprocedural Optimizations
          Assignee: unassignedbugs at nondot.org
          Reporter: mcrosier at codeaurora.org
                CC: llvm-bugs at lists.llvm.org
    Classification: Unclassified

Test case ([test-suite] SingleSource/UnitTests/2003-10-29-ScalarReplBug.c):

#include <stdio.h>

typedef struct {
  char name [80];
  int val;
  unsigned uval;
} data;

static int callback(void *d);
static void iter(int (*)(void*), void *);

static int callback(void *d)
{
  data *iter_data = (data *)d;

  printf("%u\n", iter_data->uval);
  return iter_data->uval == 0;
}

static void iter(int (*cb)(void*), void *d)
{
  cb(d);
}

int main()
{
  data d;

  d.uval = 0;
  iter(callback, &d);
  return 0;
}


On AArch64 we currently generate the following assembly:
--------------------------------------------------
    .text
    .file    "2003-10-29-ScalarReplBug.c"
    .globl    main
    .align    2
    .type    main, at function
main:                                   // @main
// BB#0:                                // %entry
    stp    x29, x30, [sp, #-16]!
    mov     x29, sp
    sub    sp, sp, #96             // =96
    add    x0, sp, #8              // =8
    str    wzr, [sp, #92]
    bl    iter
    mov     w0, wzr
    mov     sp, x29
    ldp    x29, x30, [sp], #16
    ret
.Lfunc_end0:
    .size    main, .Lfunc_end0-main

    .align    2
    .type    iter, at function
iter:                                   // @iter
// BB#0:                                // %entry
    b    callback
.Lfunc_end1:
    .size    iter, .Lfunc_end1-iter

    .align    2
    .type    callback, at function
callback:                               // @callback
// BB#0:                                // %entry
    stp    x20, x19, [sp, #-32]!
    stp    x29, x30, [sp, #16]
    mov     x19, x0
    ldr    w1, [x19, #84]
    adrp    x0, .L.str
    add    x0, x0, :lo12:.L.str
    add    x29, sp, #16            // =16
    bl    printf
    ldr    w8, [x19, #84]
    ldp    x29, x30, [sp, #16]
    cmp        w8, #0          // =0
    cset     w0, eq
    ldp    x20, x19, [sp], #32
    ret
.Lfunc_end2:
    .size    callback, .Lfunc_end2-callback

    .type    .L.str, at object          // @.str
    .section    .rodata.str1.1,"aMS", at progbits,1
.L.str:
    .asciz    "%u\n"
    .size    .L.str, 4


    .ident    "clang version 3.8.0 (trunk 257341) (llvm/trunk 257344)"
    .section    ".note.GNU-stack","", at progbits

--------------------------------------------------

Considering the body of iter is a single call to 'callback' I imagine it would
make sense to inline the call to iter.

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