[llvm-bugs] [Bug 41456] New: Suboptimal codegen for {x, y} ↦ {x+x, x+y}

[via llvm-bugs]

https://bugs.llvm.org/show_bug.cgi?id=41456

            Bug ID: 41456
           Summary: Suboptimal codegen for {x, y} ↦ {x+x, x+y}
           Product: libraries
           Version: trunk
          Hardware: PC
                OS: Linux
            Status: NEW
          Severity: enhancement
          Priority: P
         Component: Backend: X86
          Assignee: unassignedbugs at nondot.org
          Reporter: hello at dsprenkels.com
                CC: craig.topper at gmail.com, llvm-bugs at lists.llvm.org,
                    llvm-dev at redking.me.uk, spatel+llvm at rotateright.com

https://godbolt.org/z/2GE_vO

-----
The code snippet

```
#include <xmmintrin.h>

__m128i example(const __m128i vec) {
    return (__m128i){2 * vec[0], vec[0] + vec[1]};
}
```

is compiled to code that unpacks and repacks the values to the general purpose
registers. This uses 7 instructions. However, the same could easily be achieved
using

```
example:
    vpbroadcastq xmm1, xmm0
    vpaddq xmm0, xmm0, xmm1
    ret
```.

Other instructions, instead of vpbroadcastq can also be used; like vmovddup,
vpermilpd, etc.

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