[SimplifyCFG] Stop hoisting musttail calls incorrectly.

PR35774.

llvm-svn: 321603

1 files changed, 11 insertions, 0 deletions

diff --git a/llvm/lib/Transforms/Utils/SimplifyCFG.cpp b/llvm/lib/Transforms/Utils/SimplifyCFG.cpp
index 58f1e8008ea..5d5300368cc 100644
--- a/llvm/lib/Transforms/Utils/SimplifyCFG.cpp
+++ b/llvm/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;