[PATCH] D60079: [PruneEH] Don't split musttail call from ret

[Joseph Tremoulet via Phabricator via llvm-commits]

JosephTremoulet created this revision.
Herald added subscribers: llvm-commits, hiraditya.
Herald added a project: LLVM.

When inserting an `unreachable` after a noreturn call, we must ensure
that it's not a musttail call to avoid breaking the IR invariants for
musttail calls.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D60079

Files:
  llvm/lib/Transforms/IPO/PruneEH.cpp
  llvm/test/Transforms/PruneEH/musttail.ll


Index: llvm/test/Transforms/PruneEH/musttail.ll
===================================================================
--- /dev/null
+++ llvm/test/Transforms/PruneEH/musttail.ll
@@ -0,0 +1,15 @@
+; RUN: opt -prune-eh -S < %s | FileCheck %s
+
+declare void @noreturn()
+
+define void @testfn() {
+    ; A musttail call must be followed by (optional bitcast then) ret,
+    ; so make sure we don't insert an unreachable
+    ; CHECK: musttail call void @noreturn
+    ; CHECK-NOT: unreachable
+    ; CHECK-NEXT: ret void
+    musttail call void @noreturn() #0
+    ret void
+}
+
+attributes #0 = { noreturn }
Index: llvm/lib/Transforms/IPO/PruneEH.cpp
===================================================================
--- llvm/lib/Transforms/IPO/PruneEH.cpp
+++ llvm/lib/Transforms/IPO/PruneEH.cpp
@@ -203,7 +203,8 @@
 
     for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; )
       if (CallInst *CI = dyn_cast<CallInst>(I++))
-        if (CI->doesNotReturn() && !isa<UnreachableInst>(I)) {
+        if (CI->doesNotReturn() && !CI->isMustTailCall() &&
+            !isa<UnreachableInst>(I)) {
           // This call calls a function that cannot return.  Insert an
           // unreachable instruction after it and simplify the code.  Do this
           // by splitting the BB, adding the unreachable, then deleting the


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