| ; 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 |
