[Coroutines 1/2] Improve symmetric control transfer feature

Differential Revision: https://reviews.llvm.org/D76911

Author: junparser

llvm/lib/Transforms/Coroutines/CoroSplit.cpp

@@ -975,6 +975,37 @@ static bool simplifyTerminatorLeadingToRet(Instruction *InitialInst) {
   return false;
 }
 
+// Check whether CI obeys the rules of musttail attribute.
+static bool shouldBeMustTail(const CallInst &CI, const Function &F) {
+  if (CI.isInlineAsm())
+    return false;
+
+  // Match prototypes and calling conventions of resume function.
+  FunctionType *CalleeTy = CI.getFunctionType();
+  if (!CalleeTy->getReturnType()->isVoidTy() || (CalleeTy->getNumParams() != 1))
+    return false;
+
+  Type *CalleeParmTy = CalleeTy->getParamType(0);
+  if (!CalleeParmTy->isPointerTy() ||
+      (CalleeParmTy->getPointerAddressSpace() != 0))
+    return false;
+
+  if (CI.getCallingConv() != F.getCallingConv())
+    return false;
+
+  // CI should not has any ABI-impacting function attributes.
+  static const Attribute::AttrKind ABIAttrs[] = {
+      Attribute::StructRet,  Attribute::ByVal,    Attribute::InAlloca,
+      Attribute::InReg,      Attribute::Returned, Attribute::SwiftSelf,
+      Attribute::SwiftError, Attribute::Alignment};
+  AttributeList Attrs = CI.getAttributes();
+  for (auto AK : ABIAttrs)
+    if (Attrs.hasParamAttribute(0, AK))
+      return false;
+
+  return true;
+}
+
 // Add musttail to any resume instructions that is immediately followed by a
 // suspend (i.e. ret). We do this even in -O0 to support guaranteed tail call
 // for symmetrical coroutine control transfer (C++ Coroutines TS extension).
@@ -987,11 +1018,8 @@ static void addMustTailToCoroResumes(Function &F) {
   SmallVector<CallInst *, 4> Resumes;
   for (auto &I : instructions(F))
     if (auto *Call = dyn_cast<CallInst>(&I))
-      if (auto *CalledValue = Call->getCalledValue())
-        // CoroEarly pass replaced coro resumes with indirect calls to an
-        // address return by CoroSubFnInst intrinsic. See if it is one of those.
-        if (isa<CoroSubFnInst>(CalledValue->stripPointerCasts()))
-          Resumes.push_back(Call);
+      if (shouldBeMustTail(*Call, F))
+        Resumes.push_back(Call);
 
   // Set musttail on those that are followed by a ret instruction.
   for (CallInst *Call : Resumes)

llvm/test/Transforms/Coroutines/coro-split-musttail2.ll

@@ -0,0 +1,68 @@
+; Tests that coro-split will convert coro.resume followed by a suspend to a
+; musttail call.
+; RUN: opt < %s -coro-split -S | FileCheck %s
+; RUN: opt < %s -passes=coro-split -S | FileCheck %s
+
+define void @fakeresume1(i8*)  {
+entry:
+  ret void;
+}
+
+define void @fakeresume2(i64*)  {
+entry:
+  ret void;
+}
+
+define void @g() #0 {
+entry:
+  %id = call token @llvm.coro.id(i32 0, i8* null, i8* null, i8* null)
+  %alloc = call i8* @malloc(i64 16) #3
+  %vFrame = call noalias nonnull i8* @llvm.coro.begin(token %id, i8* %alloc)
+
+  %save = call token @llvm.coro.save(i8* null)
+  call fastcc void @fakeresume1(i8* null)
+
+  %suspend = call i8 @llvm.coro.suspend(token %save, i1 false)
+  switch i8 %suspend, label %exit [
+    i8 0, label %await.ready
+    i8 1, label %exit
+  ]
+await.ready:
+  %save2 = call token @llvm.coro.save(i8* null)
+  call fastcc void @fakeresume2(i64* null)
+
+  %suspend2 = call i8 @llvm.coro.suspend(token %save2, i1 false)
+  switch i8 %suspend2, label %exit [
+    i8 0, label %exit
+    i8 1, label %exit
+  ]
+exit:
+  call i1 @llvm.coro.end(i8* null, i1 false)
+  ret void
+}
+
+; Verify that in the initial function resume is not marked with musttail.
+; CHECK-LABEL: @g(
+; CHECK-NOT: musttail call fastcc void @fakeresume1(i8* null)
+
+; Verify that in the resume part resume call is marked with musttail.
+; CHECK-LABEL: @g.resume(
+; CHECK: musttail call fastcc void @fakeresume2(i64* null)
+; CHECK-NEXT: ret void
+
+declare token @llvm.coro.id(i32, i8* readnone, i8* nocapture readonly, i8*) #1
+declare i1 @llvm.coro.alloc(token) #2
+declare i64 @llvm.coro.size.i64() #3
+declare i8* @llvm.coro.begin(token, i8* writeonly) #2
+declare token @llvm.coro.save(i8*) #2
+declare i8* @llvm.coro.frame() #3
+declare i8 @llvm.coro.suspend(token, i1) #2
+declare i8* @llvm.coro.free(token, i8* nocapture readonly) #1
+declare i1 @llvm.coro.end(i8*, i1) #2
+declare i8* @llvm.coro.subfn.addr(i8* nocapture readonly, i8) #1
+declare i8* @malloc(i64)
+
+attributes #0 = { "coroutine.presplit"="1" }
+attributes #1 = { argmemonly nounwind readonly }
+attributes #2 = { nounwind }
+attributes #3 = { nounwind readnone }