[PATCH] D23441: [ppc64] Don't apply sibling call optimization if callee has any byval arg

[Chuang-Yu Cheng via llvm-commits]

cycheng added a comment.

Note that gcc is able to do SCO when caller uses more stack space than callee. Please look at this example:

  #define noinline __attribute__((noinline))
  
  struct test {
    long int a;
    char ary[56];
  };
  struct test gTest;
  
  noinline int callee(struct test v, struct test *b) { 
    b->a = v.a; 
    return 0; 
  }
  
  void caller1(struct test a, struct test c, struct test *b) { callee(gTest, b); }
  void caller2(struct test *b) { callee(gTest, b); }

Generated by gcc:

  caller1:                                caller2:
  0:  addis 2,12,.TOC.-0b at ha              0:  addis 2,12,.TOC.-0b at ha
      addi 2,2,.TOC.-0b at l                     addi 2,2,.TOC.-0b at l
      .localentry	caller1,.-caller1           .localentry	caller2,.-caller2
      std 3,32(1)                             mflr 0
      ld 3,160(1)                             addis 10,2,.LC1 at toc@ha		# gpr load fusion, type long
      addis 11,2,.LC0 at toc@ha                  ld 10,.LC1 at toc@l(10)
      ld 11,.LC0 at toc@l(11)                    std 0,16(1)
      std 31,-8(1)                            stdu 1,-112(1)
      std 4,40(1)                             std 3,96(1)
      std 5,48(1)                             ld 4,8(10)
      std 6,56(1)                             ld 3,0(10)
      std 3,96(1)                             ld 5,16(10)
      std 7,64(1)                             ld 6,24(10)
      std 8,72(1)                             ld 7,32(10)
      std 9,80(1)                             ld 8,40(10)
      std 10,88(1)                            ld 9,48(10)
      ld 31,-8(1)                             ld 10,56(10)
      ld 3,0(11)                              bl callee
      ld 4,8(11)                              addi 1,1,112
      ld 5,16(11)                             ld 0,16(1)
      ld 6,24(11)                             mtlr 0
      ld 7,32(11)                             blr
      ld 8,40(11)
      ld 9,48(11)
      ld 10,56(11)
      b callee

We can see that caller1 can sibcall to callee, but caller2 can't do that.


https://reviews.llvm.org/D23441