blob: 92663a0d095a38bc98cbe7a932f584c3f1b26edf (
plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
|
; RUN: opt < %s -passes=instcombine -S | grep "align 32" | count 2
; It's tempting to have an instcombine in which the src pointer of a
; memcpy is aligned up to the alignment of the destination, however
; there are pitfalls. If the src is an alloca, aligning it beyond what
; the target's stack pointer is aligned at will require dynamic
; stack realignment, which can require functions that don't otherwise
; need a frame pointer to need one.
;
; Abstaining from this transform is not the only way to approach this
; issue. Some late phase could be smart enough to reduce alloca
; alignments when they are greater than they need to be. Or, codegen
; could do dynamic alignment for just the one alloca, and leave the
; main stack pointer at its standard alignment.
;
@dst = global [1024 x i8] zeroinitializer, align 32
define void @foo() nounwind {
entry:
%src = alloca [1024 x i8], align 64
call void @llvm.memcpy.p0.p0.i32(ptr align 32 @dst, ptr align 32 %src, i32 1024, i1 false)
call void @frob(ptr %src) nounwind
ret void
}
declare void @frob(ptr)
declare void @llvm.memcpy.p0.p0.i32(ptr nocapture, ptr nocapture, i32, i1) nounwind
|
