[PATCH] D51165: [CodeGen] emit inline asm clobber list warnings for reserved (cont)

[Ties Stuij via Phabricator via llvm-commits]

stuij added a comment.

Unfortunately the original patch was a bit too general, in that on some architectures certain reserved registers on an asm clobber list will make sure that register isn't overridden. There's no one-to-one mapping between clobber behaviour and reserved registers.

An example of that is the PowerPC ctr register:

  volatile int a[50];
  int main(int ctr) {
  
    while(ctr--) {
      asm volatile(
          "li    29, 0"
          :
          :
          : "ctr"
                   );
  
      a[ctr] = 1;
   }
  
    return 1; // + bar(a);
  }

In this example, the use of ctr is avoided altogether, but not when it's not on the clobber list.

To avoid these kinds of false-positives, I've added a new isAsmClobberable method to TargetRegisterInfo that architectures can implement if they want to emit these asm clobber warning messages.


Repository:
  rL LLVM

https://reviews.llvm.org/D51165