[llvm-bugs] [Bug 31510] New: LLVM is unable to fold a call to pow() with complex arguments

[via llvm-bugs]

https://llvm.org/bugs/show_bug.cgi?id=31510

            Bug ID: 31510
           Summary: LLVM is unable to fold a call to pow() with complex
                    arguments
           Product: libraries
           Version: trunk
          Hardware: PC
                OS: All
            Status: NEW
          Severity: normal
          Priority: P
         Component: Scalar Optimizations
          Assignee: unassignedbugs at nondot.org
          Reporter: davide at freebsd.org
                CC: llvm-bugs at lists.llvm.org, llvm-dev at redking.me.uk,
                    simon.f.whittaker at gmail.com,
                    spatel+llvm at rotateright.com
    Classification: Unclassified

Testcase:

#include <complex>

std::complex<double> foo()
{
    using namespace std::complex_literals; 
    std::complex<double> z2 = std::pow(1i, 2);
     return z2;
}

with (-O3 -std=c++14)

Clang 3.9 output:

.LCPI0_0:
        .quad   4607182418800017408     # double 1
foo():                                # @foo()
        pushq   %rbx
        subq    $16, %rsp
        movl    $2, %ebx
        movsd   .LCPI0_0(%rip), %xmm0   # xmm0 = mem[0],zero
        xorpd   %xmm1, %xmm1
        movapd  %xmm0, %xmm5
        xorpd   %xmm4, %xmm4
        jmp     .LBB0_1
.LBB0_9:                                #   in Loop: Header=BB0_1 Depth=1
        movapd  %xmm7, %xmm0
        movapd  %xmm6, %xmm1
        movapd  %xmm4, %xmm2
        movapd  %xmm5, %xmm3
        movsd   %xmm4, 8(%rsp)          # 8-byte Spill
        movsd   %xmm5, (%rsp)           # 8-byte Spill
        callq   __muldc3
        movsd   (%rsp), %xmm5           # 8-byte Reload
        movsd   8(%rsp), %xmm4          # 8-byte Reload
.LBB0_1:                                # =>This Loop Header: Depth=1
        movapd  %xmm0, %xmm7
        movapd  %xmm1, %xmm6
        jmp     .LBB0_2
.LBB0_5:                                #   in Loop: Header=BB0_2 Depth=2
        movapd  %xmm0, %xmm2
        movapd  %xmm1, %xmm3
        movsd   %xmm6, 8(%rsp)          # 8-byte Spill
        movsd   %xmm7, (%rsp)           # 8-byte Spill
        callq   __muldc3
        movsd   (%rsp), %xmm7           # 8-byte Reload
        movsd   8(%rsp), %xmm6          # 8-byte Reload
        movapd  %xmm0, %xmm4
        movapd  %xmm1, %xmm5
        jmp     .LBB0_6
.LBB0_2:                                #   Parent Loop BB0_1 Depth=1
        movapd  %xmm4, %xmm0
        movapd  %xmm5, %xmm1
        shrl    %ebx
        je      .LBB0_10
        movapd  %xmm0, %xmm4
        mulsd   %xmm4, %xmm4
        movapd  %xmm1, %xmm2
        mulsd   %xmm2, %xmm2
        movapd  %xmm1, %xmm5
        mulsd   %xmm0, %xmm5
        subsd   %xmm2, %xmm4
        addsd   %xmm5, %xmm5
        ucomisd %xmm4, %xmm4
        jnp     .LBB0_6
        ucomisd %xmm5, %xmm5
        jp      .LBB0_5
.LBB0_6:                                #   in Loop: Header=BB0_2 Depth=2
        testb   $1, %bl
        je      .LBB0_2
        movapd  %xmm7, %xmm0
        mulsd   %xmm4, %xmm0
        movapd  %xmm6, %xmm2
        mulsd   %xmm5, %xmm2
        movapd  %xmm7, %xmm3
        mulsd   %xmm5, %xmm3
        movapd  %xmm6, %xmm1
        mulsd   %xmm4, %xmm1
        subsd   %xmm2, %xmm0
        addsd   %xmm3, %xmm1
        ucomisd %xmm0, %xmm0
        jnp     .LBB0_1
        ucomisd %xmm1, %xmm1
        jnp     .LBB0_1
        jmp     .LBB0_9
.LBB0_10:
        movapd  %xmm7, %xmm0
        movapd  %xmm6, %xmm1
        addq    $16, %rsp
        popq    %rbx
        retq


gcc7 output:

foo():
        subq    $8, %rsp
        pxor    %xmm2, %xmm2
        movsd   .LC0(%rip), %xmm3
        movapd  %xmm2, %xmm0
        movapd  %xmm3, %xmm1
        call    __muldc3
        pxor    %xmm3, %xmm3
        movsd   .LC0(%rip), %xmm2
        call    __muldc3
        addq    $8, %rsp
        ret
.LC0:
        .long   0
        .long   1072693248


Compiler explorer link if you want to play at home:
https://godbolt.org/g/GGfaei

I think this is not limited only to pow() but it's a place to start (if anybody
is interested)

-- 
You are receiving this mail because:
You are on the CC list for the bug.
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.llvm.org/pipermail/llvm-bugs/attachments/20170102/2a7edf9e/attachment-0001.html>