[coroutines][PR40979] Ignore unreachable uses across suspend points

[modocache]

Summary

Depends on https://reviews.llvm.org/D59069.

https://bugs.llvm.org/show_bug.cgi?id=40979 describes a bug in which the
-coro-split pass would assert that a use was across a suspend point from
a definition. Normally this would mean that a value would "spill" across
a suspend point and thus need to be stored in the coroutine frame. However,
in this case the use was unreachable, and so it would not be necessary
to store the definition on the frame.

To prevent the assert, simply remove unreachable basic blocks from a
coroutine function before computing spills. This avoids the assert
reported in PR40979.

[GorNishanov]

LGTM with a tiny suggestion

lib/Transforms/Coroutines/CoroSplit.cpp

931 ↗

(On Diff #189638)

I suggest to move it inside of the splitCoroutine function.

[modocache]

Thanks @GorNishanov! I moved the call into splitCoroutine. I'll land this now.

llvm/trunk/lib/Transforms/Coroutines/CoroSplit.cpp

if (&I == CoroBegin)
       break;
     if (DoNotRelocateSet.count(&I))
       continue;
     I.moveBefore(InsertPt);
   }
 }
 
 static void splitCoroutine(Function &F, CallGraph &CG, CallGraphSCC &SCC) {
+  EliminateUnreachableBlocks(F);
+
   coro::Shape Shape(F);
   if (!Shape.CoroBegin)
     return;
 
   simplifySuspendPoints(Shape);
   relocateInstructionBefore(Shape.CoroBegin, F);
   buildCoroutineFrame(F, Shape);
   replaceFrameSize(Shape);

llvm/trunk/test/Transforms/Coroutines/coro-frame-unreachable.ll

+; Check that coro-split doesn't choke on intrinsics in unreachable blocks
+; RUN: opt < %s -coro-split -S
+
+define i8* @f(i1 %arg) "coroutine.presplit"="1" personality i32 0 {
+entry:
+  %arg.addr = alloca i1
+  store i1 %arg, i1* %arg.addr
+  %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)
+  br label %cont
+
+cont:
+  %0 = call i8 @llvm.coro.suspend(token none, i1 false)
+  switch i8 %0, label %suspend [i8 0, label %resume
+                                i8 1, label %cleanup]
+resume:
+  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
+
+no.predecessors:
+  %argval = load i1, i1* %arg.addr
+  call void @print(i1 %argval)
+  br label %suspend
+
+}
+
+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 noalias i8* @malloc(i32)
+declare void @print(i1)
+declare void @free(i8*)