[llvm-bugs] [Bug 50074] New: DSE fails to remove/fold stores

[via llvm-bugs]

https://bugs.llvm.org/show_bug.cgi?id=50074

            Bug ID: 50074
           Summary: DSE fails to remove/fold stores
           Product: libraries
           Version: trunk
          Hardware: PC
                OS: Windows NT
            Status: NEW
          Severity: enhancement
          Priority: P
         Component: Scalar Optimizations
          Assignee: unassignedbugs at nondot.org
          Reporter: david.bolvansky at gmail.com
                CC: llvm-bugs at lists.llvm.org

void dse_fold(unsigned char* p, unsigned char* q, int i){
  p[i]=0;
  q[i]=0;
  // ...
  p[i]++;
}


void dse_fold2(unsigned char* p, unsigned char* q, int i){
  p[i]=0;
  q[i]=0;
  // ...
  p[i] = 1;
}

void dse_fold3(unsigned char* p, unsigned char* q, int i){
  p[i]=0;
  q[i]=0;
  // ...
  p[i] += 100;
}


LLVM -O3:
dse_fold(unsigned char*, unsigned char*, int):                       #
@dse_fold(unsigned char*, unsigned char*, int)
        movsxd  rax, edx
        mov     byte ptr [rdi + rax], 0
        mov     byte ptr [rsi + rax], 0
        add     byte ptr [rdi + rax], 1
        ret
dse_fold2(unsigned char*, unsigned char*, int):                      #
@dse_fold2(unsigned char*, unsigned char*, int)
        movsxd  rax, edx
        mov     byte ptr [rsi + rax], 0
        mov     byte ptr [rdi + rax], 1
        ret
dse_fold3(unsigned char*, unsigned char*, int):                      #
@dse_fold3(unsigned char*, unsigned char*, int)
        movsxd  rax, edx
        mov     byte ptr [rdi + rax], 0
        mov     byte ptr [rsi + rax], 0
        add     byte ptr [rdi + rax], 100
        ret

GCC -O3:
dse_fold(unsigned char*, unsigned char*, int):
        movsx   rdx, edx
        mov     BYTE PTR [rsi+rdx], 0
        mov     BYTE PTR [rdi+rdx], 1
        ret
dse_fold2(unsigned char*, unsigned char*, int):
        movsx   rdx, edx
        mov     BYTE PTR [rsi+rdx], 0
        mov     BYTE PTR [rdi+rdx], 1
        ret
dse_fold3(unsigned char*, unsigned char*, int):
        movsx   rdx, edx
        mov     BYTE PTR [rsi+rdx], 0
        mov     BYTE PTR [rdi+rdx], 100
        ret

https://godbolt.org/z/7bbrs6P5M

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