[llvm] r278144 - [X86] Don't model UD2/UD2B as a terminator

[Anton Korobeynikov via llvm-commits]

Shouldn't this be a common scenario? E.g. we model trap on ARM as
terminator as well...

On Tue, Aug 9, 2016 at 8:55 PM, David Majnemer via llvm-commits
<llvm-commits at lists.llvm.org> wrote:
> Author: majnemer
> Date: Tue Aug  9 12:55:12 2016
> New Revision: 278144
>
> URL: http://llvm.org/viewvc/llvm-project?rev=278144&view=rev
> Log:
> [X86] Don't model UD2/UD2B as a terminator
>
> A UD2 might make its way into the program via a call to @llvm.trap.
> Obviously, calls are not terminators.  However, we modeled the X86
> instruction, UD2, as a terminator.  Later on, this confuses the epilogue
> insertion machinery which results in the epilogue getting inserted
> before the UD2.  For some platforms, like x64, the result is a
> violation of the ABI.
>
> Instead, model UD2/UD2B as a side effecting instruction which may
> observe memory.
>
> Modified:
>     llvm/trunk/lib/Target/X86/X86InstrSystem.td
>     llvm/trunk/test/CodeGen/X86/x86-framelowering-trap.ll
>
> Modified: llvm/trunk/lib/Target/X86/X86InstrSystem.td
> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Target/X86/X86InstrSystem.td?rev=278144&r1=278143&r2=278144&view=diff
> ==============================================================================
> --- llvm/trunk/lib/Target/X86/X86InstrSystem.td (original)
> +++ llvm/trunk/lib/Target/X86/X86InstrSystem.td Tue Aug  9 12:55:12 2016
> @@ -23,7 +23,7 @@ let Defs = [RAX, RCX, RDX] in
>
>  // CPU flow control instructions
>
> -let isTerminator = 1, isBarrier = 1, hasCtrlDep = 1 in {
> +let mayLoad = 1, mayStore = 0, hasSideEffects = 1 in {
>    def TRAP    : I<0x0B, RawFrm, (outs), (ins), "ud2", [(trap)]>, TB;
>    def UD2B    : I<0xB9, RawFrm, (outs), (ins), "ud2b", []>, TB;
>  }
>
> Modified: llvm/trunk/test/CodeGen/X86/x86-framelowering-trap.ll
> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/CodeGen/X86/x86-framelowering-trap.ll?rev=278144&r1=278143&r2=278144&view=diff
> ==============================================================================
> --- llvm/trunk/test/CodeGen/X86/x86-framelowering-trap.ll (original)
> +++ llvm/trunk/test/CodeGen/X86/x86-framelowering-trap.ll Tue Aug  9 12:55:12 2016
> @@ -3,13 +3,18 @@ target datalayout = "e-m:e-i64:64-f80:12
>  target triple = "x86_64-unknown-linux-gnu"
>
>  ; CHECK-LABEL: bar:
> +; CHECK: pushq
>  ; CHECK: ud2
> +; CHECK-NEXT: popq
>  ; CHECK-NEXT: retq
>  define void @bar() {
>  entry:
> +  call void @callee()
>    call void @llvm.trap()
>    ret void
>  }
>
>  ; Function Attrs: noreturn nounwind
>  declare void @llvm.trap()
> +
> +declare void @callee()
>
>
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-- 
With best regards, Anton Korobeynikov
Department of Statistical Modelling, Saint Petersburg State University