[PATCH] D15232: [InstCombine] Aggressively fold compares that can be discovered to be constant

[hfinkel@anl.gov via llvm-commits]

hfinkel added a comment.

Can you provide a better example, because InstCombine seems to get the one you mentioned already (I just tried with a build using r254106):

  $ cat /tmp/f.cpp 
  bool check(bool i) {
    int f = i ? 42 : 64;
    f += 1;
    return f > 78;
  }

which eventually gets down to:

  define zeroext i1 @_Z5checkb(i1 zeroext %i) #0 {
  entry:
    %frombool = zext i1 %i to i8
    %tobool = trunc i8 %frombool to i1
    %cond = select i1 %tobool, i32 42, i32 64
    %add = add nsw i32 %cond, 1
    %cmp = icmp sgt i32 %add, 78
    ret i1 %cmp
  }

and then (after instcombine):

  ; Function Attrs: nounwind
  define zeroext i1 @_Z5checkb(i1 zeroext %i) #0 {
  entry:
    ret i1 false
  }

Beyond this, if we need further functionality in instcombine, did you consider using LVI directly?


http://reviews.llvm.org/D15232