From 8bb867a7399fbfa3483e64c15bb06f1cd67ae262 Mon Sep 17 00:00:00 2001
From: Davide Italiano <davide@freebsd.org>
Date: Sun, 31 Dec 2017 16:47:16 +0000
Subject: [PATCH] [SimplifyCFG] Stop hoisting musttail calls incorrectly.

PR35774.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@321603 91177308-0d34-0410-b5e6-96231b3b80d8
---
 lib/Transforms/Utils/SimplifyCFG.cpp   | 11 ++++++++
 test/Transforms/SimplifyCFG/pr35774.ll | 35 ++++++++++++++++++++++++++
 2 files changed, 46 insertions(+)
 create mode 100644 test/Transforms/SimplifyCFG/pr35774.ll

diff --git a/lib/Transforms/Utils/SimplifyCFG.cpp b/lib/Transforms/Utils/SimplifyCFG.cpp
index 58f1e8008ea..5d5300368cc 100644
--- a/lib/Transforms/Utils/SimplifyCFG.cpp
+++ b/lib/Transforms/Utils/SimplifyCFG.cpp
@@ -1276,6 +1276,17 @@ static bool HoistThenElseCodeToIf(BranchInst *BI,
     if (isa<TerminatorInst>(I1))
       goto HoistTerminator;
 
+    // If we're going to hoist a call, make sure that the two instructions we're
+    // commoning/hoisting are both marked with musttail, or neither of them is
+    // marked as such. Otherwise, we might end up in a situation where we hoist
+    // from a block where the terminator is a `ret` to a block where the terminator
+    // is a `br`, and `musttail` calls expect to be followed by a return.
+    auto *C1 = dyn_cast<CallInst>(I1);
+    auto *C2 = dyn_cast<CallInst>(I2);
+    if (C1 && C2)
+      if (C1->isMustTailCall() != C2->isMustTailCall())
+        return false;
+
     if (!TTI.isProfitableToHoist(I1) || !TTI.isProfitableToHoist(I2))
       return Changed;
 
diff --git a/test/Transforms/SimplifyCFG/pr35774.ll b/test/Transforms/SimplifyCFG/pr35774.ll
new file mode 100644
index 00000000000..149252085d5
--- /dev/null
+++ b/test/Transforms/SimplifyCFG/pr35774.ll
@@ -0,0 +1,35 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
+; RUN: opt -simplifycfg -S %s | FileCheck %s
+
+%foo = type { i32 (%foo)*, i32 }
+
+declare i32 @putchar(i32)
+
+define i32 @intercept(%foo %f) {
+; CHECK-LABEL: @intercept(
+; CHECK-NEXT:    [[FN:%.*]] = extractvalue [[FOO:%.*]] %f, 0
+; CHECK-NEXT:    [[X:%.*]] = extractvalue [[FOO]] %f, 1
+; CHECK-NEXT:    [[X0:%.*]] = icmp eq i32 [[X]], 0
+; CHECK-NEXT:    br i1 [[X0]], label [[ZERO:%.*]], label [[NONZERO:%.*]]
+; CHECK:       Zero:
+; CHECK-NEXT:    [[R0:%.*]] = musttail call i32 [[FN]](%foo [[F:%.*]])
+; CHECK-NEXT:    ret i32 [[R0]]
+; CHECK:       Nonzero:
+; CHECK-NEXT:    [[R1:%.*]] = tail call i32 [[FN]](%foo [[F]])
+; CHECK-NEXT:    [[TMP1:%.*]] = tail call i32 @putchar(i32 [[R1]])
+; CHECK-NEXT:    ret i32 [[R1]]
+;
+  %fn = extractvalue %foo %f, 0
+  %x = extractvalue %foo %f, 1
+  %x0 = icmp eq i32 %x, 0
+  br i1 %x0, label %Zero, label %Nonzero
+
+Zero:
+  %r0 = musttail call i32 %fn(%foo %f)
+  ret i32 %r0
+
+Nonzero:
+  %r1 = tail call i32 %fn(%foo %f)
+  %1 = tail call i32 @putchar(i32 %r1)
+  ret i32 %r1
+}
-- 
2.49.0