[llvm] c2cb093 - [Coroutine] Move all used local allocas to the .resume function

[Xun Li via llvm-commits]

Author: Xun Li
Date: 2020-11-09T17:24:49-08:00
New Revision: c2cb093d9b968f50ded99680a841d46120a114ef

URL: https://github.com/llvm/llvm-project/commit/c2cb093d9b968f50ded99680a841d46120a114ef
DIFF: https://github.com/llvm/llvm-project/commit/c2cb093d9b968f50ded99680a841d46120a114ef.diff

LOG: [Coroutine] Move all used local allocas to the .resume function

Prior to D89768, any alloca that's used after suspension points will be put on to the coroutine frame, and hence they will always be reloaded in the resume function.
However D89768 introduced a more precise way to determine whether an alloca should live on the frame. Allocas that are only used within one suspension region (hence does not need to live across suspension points) will not be put on the frame. They will remain local to the resume function.
When creating the new entry for the .resume function, the existing logic only moved all the allocas from the old entry to the new entry. This covers every alloca from the old entry. However allocas that's defined afer coro.begin are put into a separate basic block during CoroSplit (the PostSpill basic block). We need to make sure these allocas are moved to the new entry as well if they are used.
This patch walks through all allocas, and check if they are still used but are not reachable from the new entry, if so, we move them to the new entry.

Differential Revision: https://reviews.llvm.org/D90977

Added: 
    llvm/test/Transforms/Coroutines/coro-alloca-05.ll

Modified: 
    llvm/lib/Transforms/Coroutines/CoroSplit.cpp

Removed: 
    


################################################################################
diff  --git a/llvm/lib/Transforms/Coroutines/CoroSplit.cpp b/llvm/lib/Transforms/Coroutines/CoroSplit.cpp
index e46916b2d24b..c13ead98a0e2 100644
--- a/llvm/lib/Transforms/Coroutines/CoroSplit.cpp
+++ b/llvm/lib/Transforms/Coroutines/CoroSplit.cpp
@@ -606,15 +606,6 @@ void CoroCloner::replaceEntryBlock() {
   Builder.CreateUnreachable();
   BranchToEntry->eraseFromParent();
 
-  // Move any allocas into Entry that weren't moved into the frame.
-  for (auto IT = OldEntry->begin(), End = OldEntry->end(); IT != End;) {
-    Instruction &I = *IT++;
-    if (!isa<AllocaInst>(&I) || I.use_empty())
-      continue;
-
-    I.moveBefore(*Entry, Entry->getFirstInsertionPt());
-  }
-
   // Branch from the entry to the appropriate place.
   Builder.SetInsertPoint(Entry);
   switch (Shape.ABI) {
@@ -644,6 +635,19 @@ void CoroCloner::replaceEntryBlock() {
     break;
   }
   }
+
+  // Any alloca that's still being used but not reachable from the new entry
+  // needs to be moved to the new entry.
+  Function *F = OldEntry->getParent();
+  DominatorTree DT{*F};
+  for (auto IT = inst_begin(F), End = inst_end(F); IT != End;) {
+    Instruction &I = *IT++;
+    if (!isa<AllocaInst>(&I) || I.use_empty())
+      continue;
+    if (DT.isReachableFromEntry(I.getParent()))
+      continue;
+    I.moveBefore(*Entry, Entry->getFirstInsertionPt());
+  }
 }
 
 /// Derive the value of the new frame pointer.

diff  --git a/llvm/test/Transforms/Coroutines/coro-alloca-05.ll b/llvm/test/Transforms/Coroutines/coro-alloca-05.ll
new file mode 100644
index 000000000000..6176ca0c3e82
--- /dev/null
+++ b/llvm/test/Transforms/Coroutines/coro-alloca-05.ll
@@ -0,0 +1,53 @@
+; Tests that allocas after coro.begin are properly that do not need to
+; live on the frame are properly moved to the .resume function.
+; RUN: opt < %s -coro-split -S | FileCheck %s
+; RUN: opt < %s -passes=coro-split -S | FileCheck %s
+
+define i8* @f() "coroutine.presplit"="1" {
+entry:
+  %id = call token @llvm.coro.id(i32 0, i8* null, i8* null, i8* null)
+  %size = call i32 @llvm.coro.size.i32()
+  %alloc = call i8* @malloc(i32 %size)
+  %hdl = call i8* @llvm.coro.begin(token %id, i8* %alloc)
+  %x = alloca i32
+  %sp1 = call i8 @llvm.coro.suspend(token none, i1 false)
+  switch i8 %sp1, label %suspend [i8 0, label %resume
+  i8 1, label %cleanup]
+resume:
+  %x.value = load i32, i32* %x
+  call void @print(i32 %x.value)
+  br label %cleanup
+
+cleanup:
+  %mem = call i8* @llvm.coro.free(token %id, i8* %hdl)
+  call void @free(i8* %mem)
+  br label %suspend
+
+suspend:
+  call i1 @llvm.coro.end(i8* %hdl, i1 0)
+  ret i8* %hdl
+}
+
+; CHECK-LABEL: @f.resume(
+; CHECK-NEXT:  entry.resume:
+; CHECK-NEXT:    [[VFRAME:%.*]] = bitcast %f.Frame* [[FRAMEPTR:%.*]] to i8*
+; CHECK-NEXT:    [[X:%.*]] = alloca i32, align 4
+; CHECK-NEXT:    [[X_VALUE:%.*]] = load i32, i32* [[X]], align 4
+; CHECK-NEXT:    call void @print(i32 [[X_VALUE]])
+; CHECK-NEXT:    call void @free(i8* [[VFRAME]])
+; CHECK-NEXT:    ret void
+
+declare i8* @llvm.coro.free(token, i8*)
+declare i32 @llvm.coro.size.i32()
+declare i8  @llvm.coro.suspend(token, i1)
+declare void @llvm.coro.resume(i8*)
+declare void @llvm.coro.destroy(i8*)
+
+declare token @llvm.coro.id(i32, i8*, i8*, i8*)
+declare i1 @llvm.coro.alloc(token)
+declare i8* @llvm.coro.begin(token, i8*)
+declare i1 @llvm.coro.end(i8*, i1)
+
+declare void @print(i32)
+declare noalias i8* @malloc(i32)
+declare void @free(i8*)