[PATCH] D10416: Use function attribute "arm-restrict-it"

[Akira Hatanaka]

ahatanak added a comment.

Are you suggesting adding FeatureRestrictedIT to the implied feature list of HasV8Ops? I thought about doing so but found out it would make it impossible to disable restrict-it when we target v8. Try compiling the following IR with -mattr=-restrict-it after adding FeatureRestrictedIT to the implied feature list:

$ cat f1.ll
target datalayout = "e-m:e-p:32:32-i64:64-v128:64:128-a:0:32-n32-S64"
target triple = "armv8--linux-gnueabi"

define void @test_inlineasm() {
entry:

  tail call void asm sideeffect "hlt #64", ""()
  ret void

}

$ llc f1.ll -o - -mattr=-restrict-it
<inline asm>:1:2: error: instruction requires: armv8

  hlt #64
  ^

LLVM ERROR: Error parsing inline asm

This fails because disabling restrict-it transitively disables HasV8Ops too (see function ClearImpliedBits in SubtargetFeature.cpp).

If I compile the IR with trunk's llc with command line option -arm-no-restrict-it, it compiles without any errors.

$ llc f1.ll -o - -arm-no-restrict-it

Do we need the capability to turn off disable restrict-it when targeting armv8? I was assuming we do need it although I wasn't sure why users would want to do that.


http://reviews.llvm.org/D10416