[Bug target/64580] very high rs6000_stack_info() usage during LTO Firefox build on ppc64

[trippels at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=64580

--- Comment #6 from Markus Trippelsdorf <trippels at gcc dot gnu.org> ---
Annotating rs6000_stack_info() in perf shows:

       │        /* First, find out if we use _any_ altivec registers.  */
       │        for (i = FIRST_ALTIVEC_REGNO; i <= LAST_ALTIVEC_REGNO; ++i)
       │          if (df_regs_ever_live_p (i))
  0.00 │        mr     r3,r31
       │        bl     10293df0 <.df_regs_ever_live_p(unsigned int)>
  0.00 │        nop
       │        cmpdi  cr7,r3,0
       │        beq    cr7,10a7c3f4 <.rs6000_stack_info()+0xc14>
       │            mask |= ALTIVEC_REG_BIT (i);
       │        addi   r9,r31,-77
       │        srw    r9,r22,r9
       │        or     r9,r9,r24
       │        clrldi r24,r9,32
       │        if (DEFAULT_ABI == ABI_DARWIN && crtl->calls_eh_return
       │            && ! TARGET_ALTIVEC)
       │          mask |= 0xFFF;
       │
       │        /* First, find out if we use _any_ altivec registers.  */
       │        for (i = FIRST_ALTIVEC_REGNO; i <= LAST_ALTIVEC_REGNO; ++i)
  0.00 │        addi   r31,r31,1
       │        cmplwi cr7,r31,109
       │        clrldi r31,r31,32
       │        bne    cr7,10a7c3d0 <.rs6000_stack_info()+0xbf0>
       │          if (df_regs_ever_live_p (i))
       │            mask |= ALTIVEC_REG_BIT (i);
       │
       │        if (mask == 0)
  0.00 │        cmpdi  cr7,r24,0
       │        beq    cr7,10a7c5c0 <.rs6000_stack_info()+0xde0>
       │        /* Next, remove the argument registers from the set.  These
must
       │           be in the VRSAVE mask set by the caller, so we don't need to
add
       │           them in again.  More importantly, the mask we compute here
is
       │           used to generate CLOBBERs in the set_vrsave insn, and we do
not
       │           wish the argument registers to die.  */
       │        for (i = crtl->args.info.vregno - 1; i >= ALTIVEC_ARG_MIN_REG;
--i)
       │        lwa    r10,144(r29)
       │        addi   r9,r10,-1
       │        cmplwi cr7,r9,78
       │        ble    cr7,10a7c458 <.rs6000_stack_info()+0xc78>
       │        addi   r10,r10,-78
       │          mask &= ~ALTIVEC_REG_BIT (i);
       │        lis    r8,-32768
       │        clrldi r10,r10,32
       │        addi   r9,r10,-2
       │        clrldi r9,r9,32
       │        addi   r9,r9,1
       │        mtctr  r9
       │        nop
       │        nop
 99.57 │        srw    r9,r8,r10
       │        addi   r10,r10,-1
       │        andc   r9,r24,r9
  0.41 │        clrldi r10,r10,32
       │        clrldi r24,r9,32
       │        /* Next, remove the argument registers from the set.  These
must
       │           be in the VRSAVE mask set by the caller, so we don't need to
add
       │           them in again.  More importantly, the mask we compute here
is
       │           used to generate CLOBBERs in the set_vrsave insn, and we do
not
       │           wish the argument registers to die.  */
       │        for (i = crtl->args.info.vregno - 1; i >= ALTIVEC_ARG_MIN_REG;
--i)
       │        bdnz   10a7c440 <.rs6000_stack_info()+0xc60>
       │          mask &= ~ALTIVEC_REG_BIT (i);
       │
       │        /* Similarly, remove the return value from the set.  */
       │        {
       │          bool yes = false;
       │        li     r9,0
       │        mr     r4,r1
       │          diddle_return_value (is_altivec_return_reg, &yes);
       │        addis  r3,r2,-4
       │        for (i = crtl->args.info.vregno - 1; i >= ALTIVEC_ARG_MIN_REG;
--i)
       │          mask &= ~ALTIVEC_REG_BIT (i);