From 884bc6a6ed95befa128e4bcb1a1e64cf39d73117 Mon Sep 17 00:00:00 2001
From: Amir Ayupov <aaupov@fb.com>
Date: Fri, 2 Jul 2021 10:26:22 -0700
Subject: [PATCH] [X86] Modify LOOP*, HLT control flow attributes

Add missing control flow attributes:
- LOOP*: isBranch, isTerminator
- HLT: isTerminator

This helps downstream disassemblers (such as BOLT) reconstruct the control
flow graph more accurately.

Reviewed By: craig.topper

Differential Revision: https://reviews.llvm.org/D102297
---
 llvm/lib/Target/X86/X86InstrControl.td | 2 +-
 llvm/lib/Target/X86/X86InstrSystem.td  | 3 ++-
 2 files changed, 3 insertions(+), 2 deletions(-)

diff --git a/llvm/lib/Target/X86/X86InstrControl.td b/llvm/lib/Target/X86/X86InstrControl.td
index 838018e..a6cb17f 100644
--- a/llvm/lib/Target/X86/X86InstrControl.td
+++ b/llvm/lib/Target/X86/X86InstrControl.td
@@ -206,7 +206,7 @@ let isBranch = 1, isTerminator = 1, isBarrier = 1, isIndirectBranch = 1 in {
 }
 
 // Loop instructions
-let SchedRW = [WriteJump] in {
+let isBranch = 1, isTerminator = 1, SchedRW = [WriteJump] in {
 def LOOP   : Ii8PCRel<0xE2, RawFrm, (outs), (ins brtarget8:$dst), "loop\t$dst", []>;
 def LOOPE  : Ii8PCRel<0xE1, RawFrm, (outs), (ins brtarget8:$dst), "loope\t$dst", []>;
 def LOOPNE : Ii8PCRel<0xE0, RawFrm, (outs), (ins brtarget8:$dst), "loopne\t$dst", []>;
diff --git a/llvm/lib/Target/X86/X86InstrSystem.td b/llvm/lib/Target/X86/X86InstrSystem.td
index 32b00f5..48c2705 100644
--- a/llvm/lib/Target/X86/X86InstrSystem.td
+++ b/llvm/lib/Target/X86/X86InstrSystem.td
@@ -39,7 +39,8 @@ let mayLoad = 1, mayStore = 0, hasSideEffects = 1, isTrap = 1 in {
                    "ud1{q} {$src2, $src1|$src1, $src2}", []>, TB;
 }
 
-def HLT : I<0xF4, RawFrm, (outs), (ins), "hlt", []>;
+let isTerminator = 1 in
+  def HLT : I<0xF4, RawFrm, (outs), (ins), "hlt", []>;
 def RSM : I<0xAA, RawFrm, (outs), (ins), "rsm", []>, TB;
 
 // Interrupt and SysCall Instructions.
-- 
2.7.4