README.txt

define i32 @foo(i32 %a) nounwind readnone ssp {
entry:
  %and = and i32 %a, -16
  %div = sdiv i32 %and, 16
  ret i32 %div
}

but this code (X & -A)/A is X >> log2(A) when A is a power of 2, so this case
should be instcombined into just "a >> 4".

We do get this at the codegen level, so something knows about it, but 
instcombine should catch it earlier:

_foo:                                   ## @foo
## BB#0:                                ## %entry
	movl	%edi, %eax
	sarl	$4, %eax
	ret

//===---------------------------------------------------------------------===//

This code (from GCC PR28685):

int test(int a, int b) {
  int lt = a < b;
  int eq = a == b;
  if (lt)
    return 1;
  return eq;
}

Is compiled to:

define i32 @test(i32 %a, i32 %b) nounwind readnone ssp {
entry:
  %cmp = icmp slt i32 %a, %b
  br i1 %cmp, label %return, label %if.end

if.end:                                           ; preds = %entry
  %cmp5 = icmp eq i32 %a, %b
  %conv6 = zext i1 %cmp5 to i32
  ret i32 %conv6

return:                                           ; preds = %entry
  ret i32 1
}

it could be:

define i32 @test__(i32 %a, i32 %b) nounwind readnone ssp {
entry:
  %0 = icmp sle i32 %a, %b
  %retval = zext i1 %0 to i32
  ret i32 %retval
}

//===---------------------------------------------------------------------===//

This compare could fold to false:

define i1 @g(i32 a) nounwind readnone {
       %add = shl i32 %a, 1
       %mul = shl i32 %a, 1
       %cmp = icmp ugt i32 %add, %mul
       ret i1 %cmp
}

//===---------------------------------------------------------------------===//

This code can be seen in viterbi:

  %64 = call noalias i8* @malloc(i64 %62) nounwind
...
  %67 = call i64 @llvm.objectsize.i64(i8* %64, i1 false) nounwind
  %68 = call i8* @__memset_chk(i8* %64, i32 0, i64 %62, i64 %67) nounwind

llvm.objectsize.i64 should be taught about malloc/calloc, allowing it to
fold to %62.  This is a security win (overflows of malloc will get caught)
and also a performance win by exposing more memsets to the optimizer.

This occurs several times in viterbi.

//===---------------------------------------------------------------------===//