[llvm] r249522 - [X86] Emit .cfi_escape GNU_ARGS_SIZE when adjusting the stack before calls

[Kuperstein, Michael M via llvm-commits]

Thinking about it a bit more, I don’t see why it ought to be illegal for the first non-frame-setup instruction to be a CFI directive.
I’m not sure there are any examples except GNU_ARGS_SIZE – but I don’t think it makes sense to special-case it.

I’ve removed the assert in r249668.
Adrian, are you ok with that?

Michael

From: friss at apple.com [mailto:friss at apple.com]
Sent: Thursday, October 08, 2015 06:14
To: Douglas Katzman
Cc: Kuperstein, Michael M; llvm-commits at lists.llvm.org; Adrian Prantl; David Blaikie; Eric Christopher
Subject: Re: [llvm] r249522 - [X86] Emit .cfi_escape GNU_ARGS_SIZE when adjusting the stack before calls


On Oct 7, 2015, at 6:59 PM, Douglas Katzman <dougk at google.com<mailto:dougk at google.com>> wrote:

Do you happen to have a testcase handy?

The sanitizers on Linux comprise a test case it seems - they started failing with this commit.
http://lab.llvm.org:8011/builders/sanitizer-x86_64-linux/builds/20647

Without my understanding this code in the least, if you just do what the assertion says to do (as here), it fixes the sanitizers:

diff --git a/lib/Target/X86/X86FrameLowering.cpp b/lib/Target/X86/X86FrameLowering.cpp
index 7f05e5b..d85b6a8 100644
--- a/lib/Target/X86/X86FrameLowering.cpp
+++ b/lib/Target/X86/X86FrameLowering.cpp
@@ -384,8 +384,9 @@ void X86FrameLowering::BuildCFI(MachineBasicBlock &MBB,
                                 MCCFIInstruction CFIInst) const {
   MachineFunction &MF = *MBB.getParent();
   unsigned CFIIndex = MF.getMMI().addFrameInst(CFIInst);
-  BuildMI(MBB, MBBI, DL, TII.get(TargetOpcode::CFI_INSTRUCTION))
-      .addCFIIndex(CFIIndex);
+  MachineInstrBuilder MIB = BuildMI(MBB, MBBI, DL, TII.get(TargetOpcode::CFI_INSTRUCTION));
+  MIB.addCFIIndex(CFIIndex);
+  MIB->setFlag(MachineInstr::FrameSetup);
 }

This will fix the assert, but I think it is conceptually wrong. FrameSetup is supposed to describe the prologue. This will insert this flag on instructions all over the function. I can’t think of any bad consequences though. CC:ing some other people with debug info knowledge.

Fred

---------------------------------------------------------------------
Intel Israel (74) Limited

This e-mail and any attachments may contain confidential material for
the sole use of the intended recipient(s). Any review or distribution
by others is strictly prohibited. If you are not the intended
recipient, please contact the sender and delete all copies.
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.llvm.org/pipermail/llvm-commits/attachments/20151008/b4e97833/attachment.html>