[llvm-bugs] [Bug 51566] New: Missing transformation rotate(x) == 0 to x == 0

[via llvm-bugs]

https://bugs.llvm.org/show_bug.cgi?id=51566

            Bug ID: 51566
           Summary: Missing transformation rotate(x) == 0 to x == 0
           Product: libraries
           Version: trunk
          Hardware: PC
                OS: Linux
            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

bool test1(unsigned long long x)
{
  unsigned long long r = (x << 32) | (x >> 32);
  return r != 0;

}

bool test2(unsigned long long x)
{
  unsigned long long r = (x << 32) | (x >> 32);
  return r == ~0ULL;
}

Trunk -O3:
test1(unsigned long long):                              # @test1(unsigned long
long)
        rol     rdi, 32
        test    rdi, rdi
        setne   al
        ret
test2(unsigned long long):                              # @test2(unsigned long
long)
        rol     rdi, 32
        cmp     rdi, -1
        sete    al
        ret
test3(unsigned long long):                              # @test3(unsigned long
long)
        rol     rdi, 32
        test    rdi, rdi
        setne   al
        ret


Current codegen:
https://godbolt.org/z/q78xxhWe4


----------------------------------------
define i1 @src(i64 %0) {
%1:
  %2 = fshr i64 %0, i64 %0, i64 32
  %3 = icmp ne i64 %2, 0
  ret i1 %3
}
=>
define i1 @tgt(i64 %0) {
%1:
  %2 = icmp ne i64 %0, 0
  ret i1 %2
}
Transformation seems to be correct!



----------------------------------------
define i1 @src(i64 %0) {
%1:
  %2 = fshr i64 %0, i64 %0, i64 32
  %3 = icmp ne i64 %2, -1
  ret i1 %3
}
=>
define i1 @tgt(i64 %0) {
%1:
  %2 = icmp ne i64 %0, -1
  ret i1 %2
}
Transformation seems to be correct!

Alive:
https://alive2.llvm.org/ce/z/kmrBvv

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