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Diffstat (limited to 'test/Transforms/InstCombine/stack-overalign.ll')
| -rw-r--r-- | test/Transforms/InstCombine/stack-overalign.ll | 29 |
1 files changed, 29 insertions, 0 deletions
diff --git a/test/Transforms/InstCombine/stack-overalign.ll b/test/Transforms/InstCombine/stack-overalign.ll new file mode 100644 index 0000000..88b4114 --- /dev/null +++ b/test/Transforms/InstCombine/stack-overalign.ll @@ -0,0 +1,29 @@ +; 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]* %src, i32 0, i32 0 + call void @llvm.memcpy.i32(i8* getelementptr ([1024 x i8]* @dst, i32 0, i32 0), i8* %src1, i32 1024, i32 1) + call void @frob(i8* %src1) nounwind + ret void +} + +declare void @llvm.memcpy.i32(i8* nocapture, i8* nocapture, i32, i32) nounwind + +declare void @frob(i8*) |