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- ; 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
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