LLVM ERROR: Cannot select: ...

[ghost]

The llc gave me the following error:

LLVM ERROR: Cannot select: t20: i8,ch = load<LD1[%x], zext from i1> t0, FrameIndex:i16<0>, undef:i16
  t1: i16 = FrameIndex<0>
  t3: i16 = undef
In function: main

The prg.ll file:

; ModuleID = 'new_module'

define i16 @main() {
entry:
  %x = alloca i1
  store i1 true, i1* %x
  %0 = load i1, i1* %x
  %relation_op = icmp eq i1 %0, true
  br i1 %relation_op, label %then, label %else

then:                                             ; preds = %entry
  store i1 false, i1* %x
  br label %ifcont3

else:                                             ; preds = %entry
  %1 = load i1, i1* %x
  %relation_op1 = icmp eq i1 %1, false
  br i1 %relation_op1, label %then2, label %ifcont

then2:                                            ; preds = %else
  store i1 true, i1* %x
  br label %ifcont

ifcont:                                           ; preds = %then2, %else
  br label %ifcont3

ifcont3:                                          ; preds = %ifcont, %then
  ret i16 0
}

[ghost]

I changed bool type width in my compiler from i1 to i8 (x is bool). That solved my problem. But I don't know why the llc doesn't work when the bool type width is i1.

[dylanmckay]

A bunch of the LLVM backends handle i1 badly (which is pretty sad). This is why almost all frontends define bool to be i8.

I would definitely like to fix this though. By the looks of this, it is probably failing on the zext from i1 operation. All that should be needed is to promote the i1 to an i8 internally.

[dylanmckay]

This has been fixed as of 2e0ff8d2168d897362c2222c0bfce76ae5ee23f3.