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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
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