xref: /aosp_15_r20/external/llvm/test/Transforms/InstCombine/stack-overalign.ll (revision 9880d6810fe72a1726cb53787c6711e909410d58)

; RUN: opt < %s -instcombine -S | grep "align 32" | count 1

; 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 1
  %src1 = getelementptr [1024 x i8], [1024 x i8]* %src, i32 0, i32 0
  call void @llvm.memcpy.p0i8.p0i8.i32(i8* getelementptr inbounds ([1024 x i8], [1024 x i8]* @dst, i32 0, i32 0), i8* %src1, i32 1024, i32 1, i1 false)
  call void @frob(i8* %src1) nounwind
  ret void
}

declare void @frob(i8*)

declare void @llvm.memcpy.p0i8.p0i8.i32(i8* nocapture, i8* nocapture, i32, i32, i1) nounwind