[Bug middle-end/105136] New: [11/12] Missed optimization regression with 32-bit adds and shifts

[andre.schackier at gmail dot com via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105136

            Bug ID: 105136
           Summary: [11/12] Missed optimization regression with 32-bit
                    adds and shifts
           Product: gcc
           Version: 12.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: middle-end
          Assignee: unassigned at gcc dot gnu.org
          Reporter: andre.schackier at gmail dot com
  Target Milestone: ---

Given the following source code [godbolt](https://godbolt.org/z/daTxMYWKo)

#include <stdint.h>
int32_t foo(int64_t a, int32_t b, int cond) {
    if (cond) {
        a += ((int64_t)b) << 32;
    }
    return a >> 32;
}

int32_t bar(int64_t a, int32_t b, int cond) {
    int32_t r = a >> 32;
    if (cond) {
        r += b;
    }
    return r;
}

and compiling with "-O3" we get the following assembly:

foo:
        sal     rsi, 32
        mov     rax, rdi
        add     rax, rsi
        test    edx, edx
        cmove   rax, rdi
        shr     rax, 32
        ret
bar:
        sar     rdi, 32
        add     esi, edi
        test    edx, edx
        mov     eax, esi
        cmove   eax, edi
        ret

With gcc-10.3 we get for bar:
bar:
        sar     rdi, 32
        test    edx, edx
        lea     eax, [rsi+rdi]
        cmove   eax, edi
        ret

Also note that neither versions recognize that foo does the same as bar.

Credits: This was entirely found by Trevor Spiteri reported at the llvm-project
here: https://github.com/llvm/llvm-project/issues/54718