[clang] [Clang][CodeGen] Do not emit lifetime intrinsics for coro promise alloca (PR #140548)

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llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-clang

Author: Weibo He (NewSigma)

<details>
<summary>Changes</summary>

Coro promise has same lifetime as coro frame. It do not need explicit lifetime guarding. If we add lifetimes to it, middle end passes may assume promise dead after lifetime.end, leading to mis-optimizations.

Fix #<!-- -->120200 

---
Full diff: https://github.com/llvm/llvm-project/pull/140548.diff


3 Files Affected:

- (modified) clang/lib/CodeGen/CGDecl.cpp (+5) 
- (modified) clang/test/CodeGenCoroutines/coro-params.cpp (-3) 
- (modified) clang/test/CodeGenCoroutines/coro-suspend-cleanups.cpp (+1-1) 


``````````diff
diff --git a/clang/lib/CodeGen/CGDecl.cpp b/clang/lib/CodeGen/CGDecl.cpp
index 4a8f7f6a42ecb..556adebc6fa39 100644
--- a/clang/lib/CodeGen/CGDecl.cpp
+++ b/clang/lib/CodeGen/CGDecl.cpp
@@ -1343,6 +1343,11 @@ llvm::Value *CodeGenFunction::EmitLifetimeStart(llvm::TypeSize Size,
   if (!ShouldEmitLifetimeMarkers)
     return nullptr;
 
+  // No lifetimes on promise alloca, or middle end passes will assume promise
+  // dead after lifetime.end, leading to mis-optimization
+  if (Addr->getName() == "__promise")
+    return nullptr;
+
   assert(Addr->getType()->getPointerAddressSpace() ==
              CGM.getDataLayout().getAllocaAddrSpace() &&
          "Pointer should be in alloca address space");
diff --git a/clang/test/CodeGenCoroutines/coro-params.cpp b/clang/test/CodeGenCoroutines/coro-params.cpp
index 719726cca29c5..4f13e093197ff 100644
--- a/clang/test/CodeGenCoroutines/coro-params.cpp
+++ b/clang/test/CodeGenCoroutines/coro-params.cpp
@@ -84,7 +84,6 @@ void f(int val, MoveOnly moParam, MoveAndCopy mcParam, TrivialABI trivialParam)
   // CHECK-NEXT: call void @_ZN11MoveAndCopyC1EOS_(ptr {{[^,]*}} %[[McCopy]], ptr noundef nonnull align 4 dereferenceable(4) %[[McParam]]) #
   // CHECK-NEXT: call void @llvm.lifetime.start.p0(
   // CHECK-NEXT: call void @_ZN10TrivialABIC1EOS_(ptr {{[^,]*}} %[[TrivialCopy]], ptr {{[^,]*}} %[[TrivialAlloca]])
-  // CHECK-NEXT: call void @llvm.lifetime.start.p0(
   // CHECK-NEXT: invoke void @_ZNSt16coroutine_traitsIJvi8MoveOnly11MoveAndCopy10TrivialABIEE12promise_typeC1Ev(
 
   // CHECK: call void @_ZN14suspend_always12await_resumeEv(
@@ -106,7 +105,6 @@ void f(int val, MoveOnly moParam, MoveAndCopy mcParam, TrivialABI trivialParam)
 
   // Destroy promise, then parameter copies:
   // CHECK: call void @_ZNSt16coroutine_traitsIJvi8MoveOnly11MoveAndCopy10TrivialABIEE12promise_typeD1Ev(ptr {{[^,]*}} %__promise)
-  // CHECK-NEXT: call void @llvm.lifetime.end.p0(
   // CHECK-NEXT: call void @_ZN10TrivialABID1Ev(ptr {{[^,]*}} %[[TrivialCopy]])
   // CHECK-NEXT: call void @llvm.lifetime.end.p0(
   // CHECK-NEXT: call void @_ZN11MoveAndCopyD1Ev(ptr {{[^,]*}} %[[McCopy]])
@@ -135,7 +133,6 @@ void dependent_params(T x, U, U y) {
   // CHECK-NEXT: call void @_ZN1BC1EOS_(ptr {{[^,]*}} %[[unnamed_copy]], ptr noundef nonnull align 4 dereferenceable(512) %0)
   // CHECK-NEXT: call void @llvm.lifetime.start.p0(
   // CHECK-NEXT: call void @_ZN1BC1EOS_(ptr {{[^,]*}} %[[y_copy]], ptr noundef nonnull align 4 dereferenceable(512) %y)
-  // CHECK-NEXT: call void @llvm.lifetime.start.p0(
   // CHECK-NEXT: invoke void @_ZNSt16coroutine_traitsIJv1A1BS1_EE12promise_typeC1Ev(
 
   co_return;
diff --git a/clang/test/CodeGenCoroutines/coro-suspend-cleanups.cpp b/clang/test/CodeGenCoroutines/coro-suspend-cleanups.cpp
index d71c2c558996a..d028c127e1e21 100644
--- a/clang/test/CodeGenCoroutines/coro-suspend-cleanups.cpp
+++ b/clang/test/CodeGenCoroutines/coro-suspend-cleanups.cpp
@@ -52,7 +52,7 @@ coroutine ArrayInitCoro() {
     // CHECK-NEXT:  store ptr %arrayinit.element, ptr %arrayinit.endOfInit.reload.addr, align 8
     co_await Awaiter{}
     // CHECK-NEXT:  @_ZNSt14suspend_always11await_readyEv
-    // CHECK-NEXT:  br i1 %{{.+}}, label %await.ready, label %CoroSave30
+    // CHECK-NEXT:  br i1 %{{.+}}, label %await.ready, label %CoroSave29
   };
   // CHECK:       await.cleanup:                                    ; preds = %AfterCoroSuspend{{.*}}
   // CHECK-NEXT:    br label %cleanup{{.*}}.from.await.cleanup

``````````

</details>


https://github.com/llvm/llvm-project/pull/140548