[llvm-branch-commits] [llvm] release/22.x: [CoroSplit] Never collect allocas used by catchpad into frame (PR #194531)

[via llvm-branch-commits]

https://github.com/dyung updated https://github.com/llvm/llvm-project/pull/194531

>From fc4aa8f0857be616b64d2069a9c5f07049c2a9da Mon Sep 17 00:00:00 2001
From: Weibo He <NewSigma at 163.com>
Date: Wed, 25 Mar 2026 10:37:31 +0800
Subject: [PATCH] [CoroSplit] Never collect allocas used by catchpad into frame
 (#186728)

Windows EH requires exception objects allocated on stack. But there is
no reliable way to identify them. CoroSplit employs a best-effort
algorithm to determine whether allocas persist on the stack or the
frame, which may result in miscompilation when Windows exceptions are
used.
This patch proposes that we treat allocas used by catchpad as exception
objects and never place them on the frame. A verifier check is added to
enforce that operands of catchpad are either constants or allocas.

Close #143235 Close #153949 Close #182584
---
 llvm/docs/Coroutines.rst                      |  3 +
 llvm/lib/Transforms/Coroutines/SpillUtils.cpp |  7 ++
 .../Transforms/Coroutines/coro-alloca-10.ll   | 66 +++++++++++++++++++
 3 files changed, 76 insertions(+)
 create mode 100644 llvm/test/Transforms/Coroutines/coro-alloca-10.ll

diff --git a/llvm/docs/Coroutines.rst b/llvm/docs/Coroutines.rst
index 0e6b49c84acee..9fa403e68e13b 100644
--- a/llvm/docs/Coroutines.rst
+++ b/llvm/docs/Coroutines.rst
@@ -2252,4 +2252,7 @@ Areas Requiring Attention
 #. Make required changes to make sure that coroutine optimizations work with
    LTO.
 
+#. In Windows EH, exception objects must be allocated on the stack (see :ref:wineh for details).
+   We identify an exception object as an alloca that has `catchpad` users.
+
 #. More tests, more tests, more tests
diff --git a/llvm/lib/Transforms/Coroutines/SpillUtils.cpp b/llvm/lib/Transforms/Coroutines/SpillUtils.cpp
index 81fe0c9acd413..05abccf0f9a97 100644
--- a/llvm/lib/Transforms/Coroutines/SpillUtils.cpp
+++ b/llvm/lib/Transforms/Coroutines/SpillUtils.cpp
@@ -180,6 +180,13 @@ struct AllocaUseVisitor : PtrUseVisitor<AllocaUseVisitor> {
     handleAlias(I);
   }
 
+  void visitCatchPadInst(CatchPadInst &I) {
+    // Windows EH requires exception objects allocated on the stack,
+    // shortcut the traversal and keep it on stack.
+    ShouldLiveOnFrame = false;
+    Base::Worklist.clear();
+  }
+
   void visitInsertElementInst(InsertElementInst &I) {
     enqueueUsers(I);
     handleAlias(I);
diff --git a/llvm/test/Transforms/Coroutines/coro-alloca-10.ll b/llvm/test/Transforms/Coroutines/coro-alloca-10.ll
new file mode 100644
index 0000000000000..a5fb67d59edd1
--- /dev/null
+++ b/llvm/test/Transforms/Coroutines/coro-alloca-10.ll
@@ -0,0 +1,66 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --version 6
+; Test that catchpad is specially handled. Do not collect exception object into coroutine frame.
+; RUN: opt < %s -passes='coro-split,simplifycfg,early-cse' -S | FileCheck %s
+
+define void @fn() presplitcoroutine personality i32 0 {
+; CHECK-LABEL: define void @fn() personality i32 0 {
+; CHECK-NEXT:  [[ENTRY:.*:]]
+; CHECK-NEXT:    [[EXCEPTION_OBJ_RELOAD_ADDR:%.*]] = alloca ptr, align 8
+; CHECK-NEXT:    [[ID:%.*]] = call token @llvm.coro.id(i32 16, ptr null, ptr null, ptr @fn.resumers)
+; CHECK-NEXT:    [[MEM:%.*]] = call noalias nonnull ptr @malloc(i64 24)
+; CHECK-NEXT:    [[HDL:%.*]] = call noalias nonnull ptr @llvm.coro.begin(token [[ID]], ptr [[MEM]])
+; CHECK-NEXT:    store ptr @fn.resume, ptr [[HDL]], align 8
+; CHECK-NEXT:    [[DESTROY_ADDR:%.*]] = getelementptr inbounds nuw [[FN_FRAME:%.*]], ptr [[HDL]], i32 0, i32 1
+; CHECK-NEXT:    store ptr @fn.destroy, ptr [[DESTROY_ADDR]], align 8
+; CHECK-NEXT:    store ptr null, ptr [[EXCEPTION_OBJ_RELOAD_ADDR]], align 8
+; CHECK-NEXT:    [[INDEX_ADDR4:%.*]] = getelementptr inbounds nuw [[FN_FRAME]], ptr [[HDL]], i32 0, i32 2
+; CHECK-NEXT:    store i1 false, ptr [[INDEX_ADDR4]], align 1
+; CHECK-NEXT:    ret void
+;
+entry:
+  %exception.obj = alloca ptr, align 8
+  %id = call token @llvm.coro.id(i32 16, ptr null, ptr null, ptr null)
+  %size = call i64 @llvm.coro.size.i64()
+  %mem = call noalias nonnull ptr @malloc(i64 %size)
+  %hdl = call ptr @llvm.coro.begin(token %id, ptr %mem)
+  store ptr null, ptr %exception.obj, align 8
+  br label %while
+
+while:
+  %save = call token @llvm.coro.save(ptr null)
+  %suspend = call i8 @llvm.coro.suspend(token %save, i1 false)
+  switch i8 %suspend, label %coro.ret [
+  i8 0, label %await.ready
+  ]
+
+await.ready:
+  invoke void @throw()
+  to label %unreachable unwind label %catch.dispatch
+
+catch.dispatch:
+  %switch = catchswitch within none [label %catch] unwind label %ehcleanup
+
+catch:
+  %pad = catchpad within %switch [ptr null, i32 8, ptr %exception.obj]
+  invoke void @use(ptr %exception.obj) [ "funclet"(token %pad) ]
+  to label %catch.ret unwind label %ehcleanup
+
+catch.ret:
+  catchret from %pad to label %while
+
+ehcleanup:
+  %cleanup = cleanuppad within none []
+  call void @llvm.coro.end(ptr null, i1 true, token none) [ "funclet"(token %cleanup) ]
+  cleanupret from %cleanup unwind to caller
+
+coro.ret:
+  call void @llvm.coro.end(ptr null, i1 false, token none)
+  ret void
+
+unreachable:
+  unreachable
+}
+
+declare ptr @malloc(i64)
+declare void @throw()
+declare void @use(ptr)