[llvm-bugs] [Bug 34724] New: Compiler no longer optimizing some horizontal add/sub patterns after r310260

[via llvm-bugs]

https://bugs.llvm.org/show_bug.cgi?id=34724

            Bug ID: 34724
           Summary: Compiler no longer optimizing some horizontal add/sub
                    patterns after r310260
           Product: new-bugs
           Version: trunk
          Hardware: PC
                OS: Linux
            Status: NEW
          Severity: normal
          Priority: P
         Component: new bugs
          Assignee: unassignedbugs at nondot.org
          Reporter: douglas_yung at playstation.sony.com
                CC: llvm-bugs at lists.llvm.org

Prior to r310260, the compiler was optimizing some add/sub + shuffle patterns
to horizontal add/sub instructions, but no longer seems to do so.

Consider this example:

__attribute__((noinline))
__m128 add_ps_001(__m128 a, __m128 b) {
  __m128 r = (__m128){ a[0] + a[1], a[2] + a[3], b[0] + b[1], b[2] + b[3] };
  return __builtin_shufflevector(r, a, -1, 1, 2, 3);
}

When compiled with the options "-S -O2 -march=bdver2" using a compiler prior to
r310260, the compiler would generate the following assembly:

vmovaps (%rcx), %xmm0
vhaddps (%rdx), %xmm0, %xmm0
retq

After r310260, the compiler is now generating the following code for the same
function:

vmovaps (%rdx), %xmm0
vmovddup        8(%rcx), %xmm1  # xmm1 = mem[0,0]
vinsertps       $28, %xmm0, %xmm1, %xmm2 # xmm2 = xmm1[0],xmm0[0],zero,zero
vinsertps       $76, %xmm1, %xmm0, %xmm1 # xmm1 = xmm1[1],xmm0[1],zero,zero
vaddps  %xmm1, %xmm2, %xmm1
vpermilpd       $1, %xmm0, %xmm2 # xmm2 = xmm0[1,0]
vpermilps       $231, %xmm0, %xmm0 # xmm0 = xmm0[3,1,2,3]
vaddss  %xmm0, %xmm2, %xmm0
vpermilps       $208, %xmm1, %xmm1 # xmm1 = xmm1[0,0,1,3]
vinsertps       $48, %xmm0, %xmm1, %xmm0 # xmm0 = xmm1[0,1,2],xmm0[0]
retq

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