Bug 1650419 - Backport the tail merge fix to our version of Clang 9.0.1. r=dmajor

      "unpoison-thread-stacks.patch",

      "downgrade-mangling-error.patch",

      "tsan-hang-be41a98ac222.patch",

      "llvmorg-11-init-15486-gfc937806efd-dont-jump-to-landing-pads.patch",

      "loosen-msvc-detection.patch"

    ]

}

      "downgrade-mangling-error.patch",

      "rG7e18aeba5062.patch",

      "llvmorg-10-init-5191-ga84b200e604-windows-pgo.patch",

      "llvmorg-11-init-15486-gfc937806efd-dont-jump-to-landing-pads.patch",

      "loosen-msvc-detection.patch"

    ]

}

From d1c09fb47e2778538c5b1f918724d31d05497883 Mon Sep 17 00:00:00 2001

From: Arthur Eubanks <aeubanks@google.com>

Date: Wed, 13 May 2020 16:33:09 -0700

Subject: [PATCH] Don't jump to landing pads in Control Flow Optimizer

Summary: Likely fixes https://bugs.llvm.org/show_bug.cgi?id=45858.

Subscribers: hiraditya, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D80047

---

 llvm/lib/CodeGen/BranchFolding.cpp            | 18 ++++++------

 llvm/test/CodeGen/X86/branchfolding-ehpad.mir | 28 +++++++++++++++++++

 2 files changed, 38 insertions(+), 8 deletions(-)

 create mode 100644 llvm/test/CodeGen/X86/branchfolding-ehpad.mir

diff --git a/llvm/lib/CodeGen/BranchFolding.cpp b/llvm/lib/CodeGen/BranchFolding.cpp

index fb54b5d6c8d..4a822b58446 100644

--- a/llvm/lib/CodeGen/BranchFolding.cpp

+++ b/llvm/lib/CodeGen/BranchFolding.cpp

@@ -991,10 +991,10 @@ bool BranchFolder::TryTailMergeBlocks(MachineBasicBlock *SuccBB,

       continue;

     }

-    // If one of the blocks is the entire common tail (and not the entry

-    // block, which we can't jump to), we can treat all blocks with this same

-    // tail at once.  Use PredBB if that is one of the possibilities, as that

-    // will not introduce any extra branches.

+    // If one of the blocks is the entire common tail (and is not the entry

+    // block/an EH pad, which we can't jump to), we can treat all blocks with

+    // this same tail at once.  Use PredBB if that is one of the possibilities,

+    // as that will not introduce any extra branches.

     MachineBasicBlock *EntryBB =

         &MergePotentials.front().getBlock()->getParent()->front();

     unsigned commonTailIndex = SameTails.size();

@@ -1002,19 +1002,21 @@ bool BranchFolder::TryTailMergeBlocks(MachineBasicBlock *SuccBB,

     // into the other.

     if (SameTails.size() == 2 &&

         SameTails[0].getBlock()->isLayoutSuccessor(SameTails[1].getBlock()) &&

-        SameTails[1].tailIsWholeBlock())

+        SameTails[1].tailIsWholeBlock() && !SameTails[1].getBlock()->isEHPad())

       commonTailIndex = 1;

     else if (SameTails.size() == 2 &&

              SameTails[1].getBlock()->isLayoutSuccessor(

-                                                     SameTails[0].getBlock()) &&

-             SameTails[0].tailIsWholeBlock())

+                 SameTails[0].getBlock()) &&

+             SameTails[0].tailIsWholeBlock() &&

+             !SameTails[0].getBlock()->isEHPad())

       commonTailIndex = 0;

     else {

       // Otherwise just pick one, favoring the fall-through predecessor if

       // there is one.

       for (unsigned i = 0, e = SameTails.size(); i != e; ++i) {

         MachineBasicBlock *MBB = SameTails[i].getBlock();

-        if (MBB == EntryBB && SameTails[i].tailIsWholeBlock())

+        if ((MBB == EntryBB || MBB->isEHPad()) &&

+            SameTails[i].tailIsWholeBlock())

           continue;

         if (MBB == PredBB) {

           commonTailIndex = i;

diff --git a/llvm/test/CodeGen/X86/branchfolding-ehpad.mir b/llvm/test/CodeGen/X86/branchfolding-ehpad.mir

new file mode 100644

index 00000000000..d445cd20680

--- /dev/null

+++ b/llvm/test/CodeGen/X86/branchfolding-ehpad.mir

@@ -0,0 +1,28 @@

+# RUN: llc -mtriple=x86_64-windows-msvc -verify-machineinstrs -run-pass branch-folder -o - %s | FileCheck %s

+

+# Check that branch-folder does not create a fallthrough to a landing pad.

+# Also make sure that the landing pad still can be tail merged.

+---

+name: foo

+body: |

+  ; CHECK-LABEL: name: foo

+  bb.0:

+    successors: %bb.1, %bb.3

+  bb.1:

+    JCC_1 %bb.4, 5, implicit killed $eflags

+  bb.2:

+    MOV8mi $r13, 1, $noreg, 0, $noreg, 0

+    JMP_1 %bb.5

+  ; CHECK: bb.2:

+  ; CHECK-NOT: successors: {{.*}}bb.3

+  ; CHECK: bb.3 (landing-pad):

+  ; CHECK-NOT: MOV8mi

+  bb.3(landing-pad):

+    MOV8mi $r13, 1, $noreg, 0, $noreg, 0

+    JMP_1 %bb.5

+  ; CHECK: bb.4:

+  bb.4:

+    MOV8mi $r13, 2, $noreg, 0, $noreg, 0

+  bb.5:

+    RET 0

+...

-- 

2.24.1.windows.2