From 3fedc1009009d7f2e8a7e66a615c6b34c6f91969 Mon Sep 17 00:00:00 2001
From: Roman Lebedev <lebedev.ri@gmail.com>
Date: Tue, 5 Jan 2021 14:57:07 +0300
Subject: [PATCH] [NFC][SimplifyCFG] Add a test with same-destination
 condidional branch
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

Reported by Mikael Holmén as post-commit feedback on
https://reviews.llvm.org/rG2d07414ee5f74a09fb89723b4a9bb0818bdc2e18#968162
---
 lib/Transforms/Utils/SimplifyCFG.cpp          |  6 +--
 ...ional-branch-with-matching-destinations.ll | 48 +++++++++++++++++++
 2 files changed, 51 insertions(+), 3 deletions(-)
 create mode 100644 test/Transforms/SimplifyCFG/simplifyUnreachable-degenerate-conditional-branch-with-matching-destinations.ll

diff --git a/lib/Transforms/Utils/SimplifyCFG.cpp b/lib/Transforms/Utils/SimplifyCFG.cpp
index d01d9512212..cf4854d27f4 100644
--- a/lib/Transforms/Utils/SimplifyCFG.cpp
+++ b/lib/Transforms/Utils/SimplifyCFG.cpp
@@ -4690,9 +4690,9 @@ bool SimplifyCFGOpt::simplifyUnreachable(UnreachableInst *UI) {
         Changed = true;
       } else {
         Value* Cond = BI->getCondition();
-        assert(BI->getSuccessor(0) != BI->getSuccessor(1) &&
-               "Same-destination conditional branch instruction was "
-               "already canonicalized into an unconditional branch.");
+        //        assert(BI->getSuccessor(0) != BI->getSuccessor(1) &&
+        //               "Same-destination conditional branch instruction was "
+        //               "already canonicalized into an unconditional branch.");
         if (BI->getSuccessor(0) == BB) {
           Builder.CreateAssumption(Builder.CreateNot(Cond));
           Builder.CreateBr(BI->getSuccessor(1));
diff --git a/test/Transforms/SimplifyCFG/simplifyUnreachable-degenerate-conditional-branch-with-matching-destinations.ll b/test/Transforms/SimplifyCFG/simplifyUnreachable-degenerate-conditional-branch-with-matching-destinations.ll
new file mode 100644
index 00000000000..b56d9d43592
--- /dev/null
+++ b/test/Transforms/SimplifyCFG/simplifyUnreachable-degenerate-conditional-branch-with-matching-destinations.ll
@@ -0,0 +1,48 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
+; RUN: opt -S -simplifycfg -simplifycfg-require-and-preserve-domtree=0 < %s | FileCheck %s
+
+@global = external global i16, align 1
+@global.1 = external global i16, align 1
+@global.2 = external global i16, align 1
+
+define void @widget() {
+; CHECK-LABEL: @widget(
+; CHECK-NEXT:  bb:
+; CHECK-NEXT:    [[I:%.*]] = load i16, i16* @global, align 1
+; CHECK-NEXT:    [[I13:%.*]] = icmp ne i16 [[I]], 0
+; CHECK-NEXT:    call void @llvm.assume(i1 [[I13]])
+; CHECK-NEXT:    [[I17:%.*]] = load i16, i16* @global, align 1
+; CHECK-NEXT:    [[I18:%.*]] = sdiv i16 2, [[I17]]
+; CHECK-NEXT:    [[I19:%.*]] = icmp ne i16 [[I18]], 0
+; CHECK-NEXT:    [[I20:%.*]] = zext i1 [[I19]] to i16
+; CHECK-NEXT:    [[I21:%.*]] = load i16, i16* @global.1, align 1
+; CHECK-NEXT:    [[SPEC_SELECT:%.*]] = select i1 [[I19]], i16 [[I20]], i16 [[I21]]
+; CHECK-NEXT:    [[TMP0:%.*]] = xor i1 [[I19]], true
+; CHECK-NEXT:    call void @llvm.assume(i1 [[TMP0]])
+; CHECK-NEXT:    unreachable
+;
+bb:
+  %i = load i16, i16* @global, align 1
+  %i13 = icmp ne i16 %i, 0
+  br i1 %i13, label %bb16, label %bb14
+
+bb14:                                             ; preds = %bb
+  %i15 = load i16, i16* @global.1, align 1
+  br label %bb23
+
+bb16:                                             ; preds = %bb
+  %i17 = load i16, i16* @global, align 1
+  %i18 = sdiv i16 2, %i17
+  %i19 = icmp ne i16 %i18, 0
+  %i20 = zext i1 %i19 to i16
+  %i21 = load i16, i16* @global.1, align 1
+  br i1 %i19, label %bb22, label %bb23
+
+bb22:                                             ; preds = %bb16
+  br label %bb23
+
+bb23:                                             ; preds = %bb22, %bb16, %bb14
+  %i24 = phi i16 [ %i20, %bb22 ], [ %i21, %bb16 ], [ %i15, %bb14 ]
+  store i16 %i24, i16* @global.2, align 1
+  unreachable
+}