[PATCH] D148240: [Coroutines] Directly remove unnecessary lifetime intrinsics

[Nikita Popov via Phabricator via llvm-commits]

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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.

I'm also open to just dropping this check -- I'm trusting the comment that dropping the lifetime intrinsics is indeed what we want.


https://reviews.llvm.org/D148240

Files:
  llvm/lib/Transforms/Coroutines/CoroFrame.cpp
  llvm/test/Transforms/Coroutines/coro-alloca-loop-carried-address.ll


Index: llvm/test/Transforms/Coroutines/coro-alloca-loop-carried-address.ll
===================================================================
--- llvm/test/Transforms/Coroutines/coro-alloca-loop-carried-address.ll
+++ 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]])
Index: llvm/lib/Transforms/Coroutines/CoroFrame.cpp
===================================================================
--- llvm/lib/Transforms/Coroutines/CoroFrame.cpp
+++ llvm/lib/Transforms/Coroutines/CoroFrame.cpp
@@ -1946,11 +1946,13 @@
       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);
     }


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