[LLVMdev] Unnecessary i16 -> i32 type promotion

[Marc de Kruijf]

If I have an '&' operator inside an 'if' statement, LLVM seems to always
promote a 16 bit integer type to a 32 bit integer type.  I don't want this
to happen because my back-end only supports 16 bit types.  Why is this
happening?  Where might this be happening, so I can fix it?  It doesn't seem
to happen with the '|' operator, only '&'.  Thanks!

Code is below.  Relevant code highlighted in *bold*.


C Function:
-------------------

$cat test.c
short foo(short a) {
  if *(a & 1)*
    return -1;
  else
    return 1;
}

LLVM:
---------------------

$ cat test.ll
; ModuleID = 'test.o'
target datalayout =
"e-p:32:32:32-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:32:64-f32:32:32-f64:32:64-v64:64:64-v128:128:128-a0:0:64-f80:32:32"
target triple = "i386-pc-linux-gnu"

define signext i16 @foo(i16 signext %a) nounwind readnone {
entry:
        *%0 = zext i16 %a to i32         ; <i32> [#uses=1]*
        %1 = and i32 %0, 1              ; <i32> [#uses=1]
        %toBool = icmp eq i32 %1, 0             ; <i1> [#uses=1]
        %.0 = select i1 %toBool, i16 1, i16 -1          ; <i16> [#uses=1]
        ret i16 %.0
}
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