[Bug target/68752] PowerPC: vector reciprocal square root estimate missed optimisations

["cel at us dot ibm.com" <gcc-bugzilla at gcc dot gnu dot org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=68752

--- Comment #3 from Carl Love <cel at us dot ibm.com> ---
I investigated the issue using GCC 6.1. The t1() function from file
recip-vec-sqrtf.c file is as follows:

void t1(void)
{
int i;

for (i = 0; i < 4; i++)
  r[i] = a[i] / sqrtf (b[i]);
}

The assembly code being generated for the loop using the options specified in
the bug plus -S to generate the assembly code results in the following

 -O2 -ffast-math -ftree-vectorize -mcpu=power7 -mrecip -fno-common  -S 

.file "recip-vec-sqrtf.c"
.section ".toc","aw"
.section ".text"
.machine power7
.align 2
.p2align 4,,15
.globl t1
.section ".opd","aw"
.align 3
t1:
.quad .L.t1,.TOC.@tocbase
.previous
.type t1, @function
.L.t1:
addis 9,2,.LANCHOR0@toc@ha
addis 10,2,.LC0@toc@ha
addi 9,9,.LANCHOR0@toc@l
addi 10,10,.LC0@toc@l
lxvd2x 12,0,9
lxvd2x 11,0,10
li 10,32
lxvd2x 10,9,10
li 10,16
xvrsqrtesp 0,12
xvmsubasp 12,12,11
xvmulsp 9,0,0
xvnmsubasp 11,12,9
xvmulsp 0,0,11
xvmulsp 0,0,10
stxvd2x 0,9,10
blr

The expected vector instructions are there.  It does not appear that any scalar
instructions are being generated for the computation as implied in the
bugzilla.

The other loops for the test cases in attachment 36938 are similar in that they
appear to only be generating the expected vector instructions.  The bugzilla
was filed before GCC 6 was released.  It appears the issue has since been
fixed.