[Bug tree-optimization/19939] New: -finline-functions inhibits tail recursion accumulation optimization

[falk at debian dot org]

falk@juist:/tmp% cat test.c
unsigned long ipow(unsigned long a, unsigned long b) {
    if (b == 0)
        return 1;
    else
        return a * ipow(a, b - 1);
}

falk@juist:/tmp% gcc -c -O2 test.c && objdump -d test.o              

test.o:     file format elf64-alpha

Disassembly of section .text:

0000000000000000 <ipow>:
   0:   01 00 1f 20     lda     v0,1
   4:   05 00 20 e6     beq     a1,1c <ipow+0x1c>
   8:   1f 04 ff 47     nop
   c:   00 00 fe 2f     unop
  10:   ff ff 31 22     lda     a1,-1(a1)
  14:   00 04 10 4c     mulq    v0,a0,v0
  18:   fd ff 3f f6     bne     a1,10 <ipow+0x10>
  1c:   01 80 fa 6b     ret

The recursion was nicely transformed to a branch.

falk@juist:/tmp% gcc -c -O2 test.c -finline-functions && objdump -d test.o

test.o:     file format elf64-alpha

Disassembly of section .text:

0000000000000000 <ipow>:
   0:   00 00 bb 27     ldah    gp,0(t12)
   4:   00 00 bd 23     lda     gp,0(gp)
   8:   f0 ff de 23     lda     sp,-16(sp)
   c:   01 00 1f 20     lda     v0,1
  10:   08 00 3e b5     stq     s0,8(sp)
  14:   00 00 5e b7     stq     ra,0(sp)
  18:   09 04 f0 47     mov     a0,s0
  1c:   1c 00 20 e6     beq     a1,90 <ipow+0x90>
  20:   a1 35 20 42     cmpeq   a1,0x1,t0
  24:   19 00 20 f4     bne     t0,8c <ipow+0x8c>
  28:   a1 55 20 42     cmpeq   a1,0x2,t0
  2c:   01 00 5f 20     lda     t1,1
  30:   15 00 20 f4     bne     t0,88 <ipow+0x88>
  34:   a1 75 20 42     cmpeq   a1,0x3,t0
  38:   12 00 20 f4     bne     t0,84 <ipow+0x84>
  3c:   a1 95 20 42     cmpeq   a1,0x4,t0
  40:   0f 00 20 f4     bne     t0,80 <ipow+0x80>
  44:   a1 b5 20 42     cmpeq   a1,0x5,t0
  48:   0c 00 20 f4     bne     t0,7c <ipow+0x7c>
  4c:   a1 d5 20 42     cmpeq   a1,0x6,t0
  50:   09 00 20 f4     bne     t0,78 <ipow+0x78>
  54:   a1 f5 20 42     cmpeq   a1,0x7,t0
  58:   06 00 20 f4     bne     t0,74 <ipow+0x74>
  5c:   a1 15 21 42     cmpeq   a1,0x8,t0
  60:   03 00 20 f4     bne     t0,70 <ipow+0x70>
  64:   f7 ff 31 22     lda     a1,-9(a1)
  68:   00 00 40 d3     bsr     ra,6c <ipow+0x6c>
  6c:   02 04 20 4d     mulq    s0,v0,t1
  70:   02 04 49 4c     mulq    t1,s0,t1
  74:   02 04 49 4c     mulq    t1,s0,t1
  78:   02 04 49 4c     mulq    t1,s0,t1
  7c:   02 04 49 4c     mulq    t1,s0,t1
  80:   02 04 49 4c     mulq    t1,s0,t1
  84:   02 04 49 4c     mulq    t1,s0,t1
  88:   00 04 49 4c     mulq    t1,s0,v0
  8c:   00 04 09 4c     mulq    v0,s0,v0
  90:   00 00 5e a7     ldq     ra,0(sp)
  94:   08 00 3e a5     ldq     s0,8(sp)
  98:   10 00 de 23     lda     sp,16(sp)
  9c:   01 80 fa 6b     ret

But here the recursion is back. It looks like the function was inlined into
itself too early.

-- 
           Summary: -finline-functions inhibits tail recursion accumulation
                    optimization
           Product: gcc
           Version: 4.0.0
            Status: UNCONFIRMED
          Keywords: missed-optimization
          Severity: normal
          Priority: P2
         Component: tree-optimization
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: falk at debian dot org
                CC: gcc-bugs at gcc dot gnu dot org
 GCC build triplet: alphaev68-unknown-linux-gnu
  GCC host triplet: alphaev68-unknown-linux-gnu
GCC target triplet: alphaev68-unknown-linux-gnu


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=19939