[AArch64] copy incorrectly erased and discard zero-extend operation

[llvmbot]

Bugzilla Link	48066
Version	trunk
OS	Linux
Reporter	LLVM Bugzilla Contributor
CC	@Arnaud-de-Grandmaison-ARM,@DMG862,@smithp35

Extended Description

$ clang -O3 test-case.ll -w ;./a.out
c = -8917
$ clang -O0 test-case.ll -w ;./a.out
c = 4294958379

@​b = dso_local local_unnamed_addr global { [3 x i8], i8, i8, i8, i8, i8 } { [3 x i8] undef, i8 -64, i8 74, i8 -9, i8 -1, i8 7 }, align 8
@​c = common dso_local local_unnamed_addr global i64 0, align 8
@.str = private unnamed_addr constant [9 x i8] c"c = %ld\0A\00", align 1

define dso_local i8 @​d(i64 %h) local_unnamed_addr {
entry:
ret i8 undef
}

declare dso_local i32 @​printf(i8* nocapture readonly, ...) local_unnamed_addr

define dso_local i32 @​main() local_unnamed_addr {
entry:
%bf.load = load i64, i64* bitcast ({ [3 x i8], i8, i8, i8, i8, i8 }* @​b to i64*), align 8
%0 = lshr i64 %bf.load, 30
%sext3 = shl nuw nsw i64 %0, 16
%sext = trunc i64 %sext3 to i32
%conv.i = ashr exact i32 %sext, 16
%conv.i.i = zext i32 %conv.i to i64
store i64 %conv.i.i, i64* @​c, align 8
%call.i.i = tail call i32 (i8*, ...) @​printf(i8* nonnull dereferenceable(1) getelementptr inbounds ([9 x i8], [9 x i8]* @.str, i64 0, i64 0), i64 %conv.i.i)
%call4.i = tail call i8 bitcast (i8 (i64)* @​d to i8 (i32, i32)*)(i32 0, i32 %conv.i)
ret i32 0
}

[c-rhodes]

now fixed: https://godbolt.org/z/xW579rzTY

I managed to reproduce the issue on LLVM 11: https://godbolt.org/z/6saK44nf9

It's been fixed since LLVM 12.