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30 lines
1.2 KiB
LLVM
30 lines
1.2 KiB
LLVM
; RUN: llvm-as < %s | opt -instcombine | llvm-dis | grep {align 32} | count 1
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; It's tempting to have an instcombine in which the src pointer of a
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; memcpy is aligned up to the alignment of the destination, however
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; there are pitfalls. If the src is an alloca, aligning it beyond what
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; the target's stack pointer is aligned at will require dynamic
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; stack realignment, which can require functions that don't otherwise
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; need a frame pointer to need one.
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;
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; Abstaining from this transform is not the only way to approach this
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; issue. Some late phase could be smart enough to reduce alloca
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; alignments when they are greater than they need to be. Or, codegen
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; could do dynamic alignment for just the one alloca, and leave the
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; main stack pointer at its standard alignment.
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@dst = global [1024 x i8] zeroinitializer, align 32
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define void @foo() nounwind {
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entry:
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%src = alloca [1024 x i8], align 1
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%src1 = getelementptr [1024 x i8]* %src, i32 0, i32 0
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call void @llvm.memcpy.i32(i8* getelementptr ([1024 x i8]* @dst, i32 0, i32 0), i8* %src1, i32 1024, i32 1)
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call void @frob(i8* %src1) nounwind
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ret void
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}
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declare void @llvm.memcpy.i32(i8* nocapture, i8* nocapture, i32, i32) nounwind
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declare void @frob(i8*)
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