$ cat add.c
#include <stdint.h>
uint16_t add(uint16_t a, uint16_t b) {
  return a+b;
}
$ clang-7 -S -emit-llvm add.c -o - |opt-7 -O2 -S
; ModuleID = '<stdin>'
source_filename = "add.c"
target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
target triple = "x86_64-pc-linux-gnu"

; Function Attrs: noinline nounwind optnone uwtable
define dso_local zeroext i16 @add(i16 zeroext, i16 zeroext) local_unnamed_addr #0 {
  %3 = alloca i16, align 2
  %4 = alloca i16, align 2
  store i16 %0, i16* %3, align 2
  store i16 %1, i16* %4, align 2
  %5 = load i16, i16* %3, align 2
  %6 = zext i16 %5 to i32
  %7 = load i16, i16* %4, align 2
  %8 = zext i16 %7 to i32
  %9 = add nsw i32 %6, %8
  %10 = trunc i32 %9 to i16
  ret i16 %10
}

attributes #0 = { noinline nounwind optnone uwtable "correctly-rounded-divide-sqrt-fp-math"="false" "disable-tail-calls"="false" "less-precise-fpmad"="false" "no-frame-pointer-elim"="true" "no-frame-pointer-elim-non-leaf" "no-infs-fp-math"="false" "no-jump-tables"="false" "no-nans-fp-math"="false" "no-signed-zeros-fp-math"="false" "no-trapping-math"="false" "stack-protector-buffer-size"="8" "target-cpu"="x86-64" "target-features"="+fxsr,+mmx,+sse,+sse2,+x87" "unsafe-fp-math"="false" "use-soft-float"="false" }

!llvm.module.flags = !{!0}
!llvm.ident = !{!1}

!0 = !{i32 1, !"wchar_size", i32 4}
!1 = !{!"clang version 7.0.0-5 (tags/RELEASE_700/final)"}
$ clang-7 -S -emit-llvm add.c -o - |clang-7 -O2 -S -emit-llvm -o - -x ir -
; ModuleID = '<stdin>'
source_filename = "add.c"
target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
target triple = "x86_64-pc-linux-gnu"

; Function Attrs: noinline nounwind optnone uwtable
define dso_local zeroext i16 @add(i16 zeroext, i16 zeroext) local_unnamed_addr #0 {
  %3 = alloca i16, align 2
  %4 = alloca i16, align 2
  store i16 %0, i16* %3, align 2
  store i16 %1, i16* %4, align 2
  %5 = load i16, i16* %3, align 2
  %6 = zext i16 %5 to i32
  %7 = load i16, i16* %4, align 2
  %8 = zext i16 %7 to i32
  %9 = add nsw i32 %6, %8
  %10 = trunc i32 %9 to i16
  ret i16 %10
}

attributes #0 = { noinline nounwind optnone uwtable "correctly-rounded-divide-sqrt-fp-math"="false" "disable-tail-calls"="false" "less-precise-fpmad"="false" "no-frame-pointer-elim"="true" "no-frame-pointer-elim-non-leaf" "no-infs-fp-math"="false" "no-jump-tables"="false" "no-nans-fp-math"="false" "no-signed-zeros-fp-math"="false" "no-trapping-math"="false" "stack-protector-buffer-size"="8" "target-cpu"="x86-64" "target-features"="+fxsr,+mmx,+sse,+sse2,+x87" "unsafe-fp-math"="false" "use-soft-float"="false" }

!llvm.module.flags = !{!0}
!llvm.ident = !{!1}

!0 = !{i32 1, !"wchar_size", i32 4}
!1 = !{!"clang version 7.0.0-5 (tags/RELEASE_700/final)"}
$ clang-7 -S -emit-llvm add.c -O2 -o -
; ModuleID = 'add.c'
source_filename = "add.c"
target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
target triple = "x86_64-pc-linux-gnu"

; Function Attrs: norecurse nounwind readnone uwtable
define dso_local zeroext i16 @add(i16 zeroext, i16 zeroext) local_unnamed_addr #0 {
  %3 = add i16 %1, %0
  ret i16 %3
}

attributes #0 = { norecurse nounwind readnone uwtable "correctly-rounded-divide-sqrt-fp-math"="false" "disable-tail-calls"="false" "less-precise-fpmad"="false" "no-frame-pointer-elim"="false" "no-infs-fp-math"="false" "no-jump-tables"="false" "no-nans-fp-math"="false" "no-signed-zeros-fp-math"="false" "no-trapping-math"="false" "stack-protector-buffer-size"="8" "target-cpu"="x86-64" "target-features"="+fxsr,+mmx,+sse,+sse2,+x87" "unsafe-fp-math"="false" "use-soft-float"="false" }

!llvm.module.flags = !{!0}
!llvm.ident = !{!1}

!0 = !{i32 1, !"wchar_size", i32 4}
!1 = !{!"clang version 7.0.0-5 (tags/RELEASE_700/final)"}