[Coroutines] Directly remove unnecessary lifetime intrinsics

The insertSpills() code will currently skip lifetime intrinsic users
when replacing the alloca with a frame reference. Rather than
leaving behind the dead lifetime intrinsics working on the old
alloca, directly remove them. This makes sure the alloca can be
dropped as well.

I noticed this as a regression when converting tests to opaque
pointers. Without opaque pointers, this code didn't really do
anything, because there would usually be a bitcast in between.
The lifetimes would get rewritten to the frame pointer. With
opaque pointers, this code now triggers and leaves behind users
of the old allocas.

Differential Revision: https://reviews.llvm.org/D148240

Author: nikic

clang/test/CodeGenCoroutines/coro-always-inline.cpp

@@ -33,11 +33,8 @@ struct coroutine_traits {
 
 // CHECK-LABEL: @_Z3foov
 // CHECK-LABEL: entry:
-// CHECK: call void @llvm.lifetime.start.p0(i64 1, ptr %ref.tmp{{.*}})
-// CHECK: call void @llvm.lifetime.end.p0(i64 1, ptr %ref.tmp{{.*}})
-
-// CHECK: call void @llvm.lifetime.start.p0(i64 1, ptr %ref.tmp{{.*}})
-// CHECK: call void @llvm.lifetime.end.p0(i64 1, ptr %ref.tmp{{.*}})
+// CHECK: %ref.tmp.reload.addr = getelementptr
+// CHECK: %ref.tmp4.reload.addr = getelementptr
 void foo() { co_return; }
 
 // Check that bar is not inlined even it's marked as always_inline.

llvm/lib/Transforms/Coroutines/CoroFrame.cpp

@@ -1946,11 +1946,13 @@ static void insertSpills(const FrameDataInfo &FrameData, coro::Shape &Shape) {
       DVI->replaceUsesOfWith(Alloca, G);
 
     for (Instruction *I : UsersToUpdate) {
-      // It is meaningless to remain the lifetime intrinsics refer for the
+      // It is meaningless to retain the lifetime intrinsics refer for the
       // member of coroutine frames and the meaningless lifetime intrinsics
       // are possible to block further optimizations.
-      if (I->isLifetimeStartOrEnd())
+      if (I->isLifetimeStartOrEnd()) {
+        I->eraseFromParent();
         continue;
+      }
 
       I->replaceUsesOfWith(Alloca, G);
     }

llvm/test/Transforms/Coroutines/coro-alloca-loop-carried-address.ll

@@ -7,7 +7,6 @@
 define void @foo() presplitcoroutine {
 ; CHECK-LABEL: @foo(
 ; CHECK-NEXT:  entry:
-; CHECK-NEXT:    [[STACKVAR0:%.*]] = alloca i64, align 8
 ; CHECK-NEXT:    [[ID:%.*]] = call token @llvm.coro.id(i32 0, ptr null, ptr null, ptr @foo.resumers)
 ; CHECK-NEXT:    [[ALLOC:%.*]] = call ptr @malloc(i64 40)
 ; CHECK-NEXT:    [[VFRAME:%.*]] = call noalias nonnull ptr @llvm.coro.begin(token [[ID]], ptr [[ALLOC]])