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llvm-project/llvm/test/CodeGen/XCore/align.ll

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[XCore] Prefer to word align functions. The behaviour of the XCore's instruction buffer means that the performance of the same code sequence can differ depending on whether it starts at a 4 byte aligned address or not. Since we don't model the instruction buffer in the backend we have no way of knowing for sure if it is beneficial to word align a specific function. However, in the absence of precise modelling, it is better on balance to word align functions because: * It makes a fetch-nop while executing the prologue slightly less likely. * If we don't word align functions then a small perturbation in one function can have a dramatic knock on effect. If the size of the function changes it might change the alignment and therefore the performance of all the functions that happen to follow it in the binary. This butterfly effect makes it harder to reason about and measure the performance of code. llvm-svn: 202163
2014-02-26 00:37:15 +08:00
; RUN: llc < %s -march=xcore | FileCheck %s
; CHECK: .align 4
; CHECK-LABEL: f:
define void @f() nounwind {
entry:
ret void
}
; CHECK: .align 2
; CHECK-LABEL: g:
define void @g() nounwind optsize {
entry:
ret void
}