[coro][pgo] Do not insert counters in the suspend block (llvm#71262)

If we did, we couldn't lower symmetric transfer resumes to tail calls.

We can instrument the other 2 edges instead, as long as they also don't
point to the same basic block.

llvm/include/llvm/Transforms/Instrumentation/CFGMST.h

@@ -19,6 +19,8 @@
 #include "llvm/Analysis/BlockFrequencyInfo.h"
 #include "llvm/Analysis/BranchProbabilityInfo.h"
 #include "llvm/Analysis/CFG.h"
+#include "llvm/IR/Instructions.h"
+#include "llvm/IR/IntrinsicInst.h"
 #include "llvm/Support/BranchProbability.h"
 #include "llvm/Support/Debug.h"
 #include "llvm/Support/raw_ostream.h"
@@ -82,6 +84,38 @@ template <class Edge, class BBInfo> class CFGMST {
     return true;
   }
 
+  void handleCoroSuspendEdge(Edge *E) {
+    // We must not add instrumentation to the BB representing the
+    // "suspend" path, else CoroSplit won't be able to lower
+    // llvm.coro.suspend to a tail call. We do want profiling info for
+    // the other branches (resume/destroy). So we do 2 things:
+    // 1. we prefer instrumenting those other edges by setting the weight
+    //    of the "suspend" edge to max, and
+    // 2. we mark the edge as "Removed" to guarantee it is not considered
+    //    for instrumentation. That could technically happen:
+    //    (from test/Transforms/Coroutines/coro-split-musttail.ll)
+    //
+    // %suspend = call i8 @llvm.coro.suspend(token %save, i1 false)
+    // switch i8 %suspend, label %exit [
+    //   i8 0, label %await.ready
+    //   i8 1, label %exit
+    // ]
+    const BasicBlock *EdgeTarget = E->DestBB;
+    if (!EdgeTarget)
+      return;
+    assert(E->SrcBB);
+    const Function *F = EdgeTarget->getParent();
+    if (!F->isPresplitCoroutine())
+      return;
+
+    const Instruction *TI = E->SrcBB->getTerminator();
+    if (auto *SWInst = dyn_cast<SwitchInst>(TI))
+      if (auto *Intrinsic = dyn_cast<IntrinsicInst>(SWInst->getCondition()))
+        if (Intrinsic->getIntrinsicID() == Intrinsic::coro_suspend &&
+            SWInst->getDefaultDest() == EdgeTarget)
+          E->Removed = true;
+  }
+
   // Traverse the CFG using a stack. Find all the edges and assign the weight.
   // Edges with large weight will be put into MST first so they are less likely
   // to be instrumented.
@@ -133,6 +167,7 @@ template <class Edge, class BBInfo> class CFGMST {
             Weight++;
           auto *E = &addEdge(&BB, TargetBB, Weight);
           E->IsCritical = Critical;
+          handleCoroSuspendEdge(E);
           LLVM_DEBUG(dbgs() << "  Edge: from " << BB.getName() << " to "
                             << TargetBB->getName() << "  w=" << Weight << "\n");
 

llvm/test/Instrumentation/InstrProfiling/Coro/coro-split-musttail.ll

@@ -0,0 +1,63 @@
+; Tests that instrumentation doesn't interfere with lowering (coro-split).
+; It should convert coro.resume followed by a suspend to a musttail call.
+
+; RUN: opt < %s -passes='pgo-instr-gen,cgscc(coro-split),simplifycfg,early-cse' -S | FileCheck %s
+
+define void @f() #0 {
+entry:
+  %id = call token @llvm.coro.id(i32 0, ptr null, ptr null, ptr null)
+  %alloc = call ptr @malloc(i64 16) #3
+  %vFrame = call noalias nonnull ptr @llvm.coro.begin(token %id, ptr %alloc)
+
+  %save = call token @llvm.coro.save(ptr null)
+  %addr1 = call ptr @llvm.coro.subfn.addr(ptr null, i8 0)
+  call fastcc void %addr1(ptr 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(ptr null)
+  %addr2 = call ptr @llvm.coro.subfn.addr(ptr null, i8 0)
+  call fastcc void %addr2(ptr 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(ptr null, i1 false, token none)
+  ret void
+}
+
+; Verify that in the initial function resume is not marked with musttail.
+; CHECK-LABEL: @f(
+; CHECK: %[[addr1:.+]] = call ptr @llvm.coro.subfn.addr(ptr null, i8 0)
+; CHECK-NOT: musttail call fastcc void %[[addr1]](ptr null)
+
+; Verify that in the resume part resume call is marked with musttail.
+; CHECK-LABEL: @f.resume(
+; CHECK: %[[addr2:.+]] = call ptr @llvm.coro.subfn.addr(ptr null, i8 0)
+; CHECK: call void @llvm.instrprof
+; CHECK-NEXT: musttail call fastcc void %[[addr2]](ptr null)
+; CHECK-NEXT: ret void
+
+declare token @llvm.coro.id(i32, ptr readnone, ptr nocapture readonly, ptr) #1
+declare i1 @llvm.coro.alloc(token) #2
+declare i64 @llvm.coro.size.i64() #3
+declare ptr @llvm.coro.begin(token, ptr writeonly) #2
+declare token @llvm.coro.save(ptr) #2
+declare ptr @llvm.coro.frame() #3
+declare i8 @llvm.coro.suspend(token, i1) #2
+declare ptr @llvm.coro.free(token, ptr nocapture readonly) #1
+declare i1 @llvm.coro.end(ptr, i1, token) #2
+declare ptr @llvm.coro.subfn.addr(ptr nocapture readonly, i8) #1
+declare ptr @malloc(i64)
+
+attributes #0 = { presplitcoroutine }
+attributes #1 = { argmemonly nounwind readonly }
+attributes #2 = { nounwind }
+attributes #3 = { nounwind readnone }

llvm/test/Instrumentation/InstrProfiling/Coro/coro-split-musttail1.ll

@@ -0,0 +1,97 @@
+; Tests that instrumentation doesn't interfere with lowering (coro-split).
+; It should convert coro.resume followed by a suspend to a musttail call.
+
+; RUN: opt < %s -passes='pgo-instr-gen,cgscc(coro-split),simplifycfg,early-cse' -S | FileCheck %s
+
+define void @f() #0 {
+entry:
+  %id = call token @llvm.coro.id(i32 0, ptr null, ptr null, ptr null)
+  %alloc = call ptr @malloc(i64 16) #3
+  %vFrame = call noalias nonnull ptr @llvm.coro.begin(token %id, ptr %alloc)
+
+  %save = call token @llvm.coro.save(ptr null)
+  %addr1 = call ptr @llvm.coro.subfn.addr(ptr null, i8 0)
+  call fastcc void %addr1(ptr null)
+
+  %suspend = call i8 @llvm.coro.suspend(token %save, i1 false)
+  switch i8 %suspend, label %exit [
+    i8 0, label %await.suspend
+    i8 1, label %exit
+  ]
+await.suspend:
+  %save2 = call token @llvm.coro.save(ptr null)
+  %br0 = call i8 @switch_result()
+  switch i8 %br0, label %unreach [
+    i8 0, label %await.resume3
+    i8 1, label %await.resume1
+    i8 2, label %await.resume2
+  ]
+await.resume1:
+  %hdl = call ptr @g()
+  %addr2 = call ptr @llvm.coro.subfn.addr(ptr %hdl, i8 0)
+  call fastcc void %addr2(ptr %hdl)
+  br label %final.suspend
+await.resume2:
+  %hdl2 = call ptr @h()
+  %addr3 = call ptr @llvm.coro.subfn.addr(ptr %hdl2, i8 0)
+  call fastcc void %addr3(ptr %hdl2)
+  br label %final.suspend
+await.resume3:
+  %addr4 = call ptr @llvm.coro.subfn.addr(ptr null, i8 0)
+  call fastcc void %addr4(ptr null)
+  br label %final.suspend
+final.suspend:
+  %suspend2 = call i8 @llvm.coro.suspend(token %save2, i1 false)
+  switch i8 %suspend2, label %exit [
+    i8 0, label %pre.exit
+    i8 1, label %exit
+  ]
+pre.exit:
+  br label %exit
+exit:
+  call i1 @llvm.coro.end(ptr null, i1 false, token none)
+  ret void
+unreach:
+  unreachable
+}
+
+; Verify that in the initial function resume is not marked with musttail.
+; CHECK-LABEL: @f(
+; CHECK: %[[addr1:.+]] = call ptr @llvm.coro.subfn.addr(ptr null, i8 0)
+; CHECK-NOT: musttail call fastcc void %[[addr1]](ptr null)
+
+; Verify that in the resume part resume call is marked with musttail.
+; CHECK-LABEL: @f.resume(
+; CHECK: %[[hdl:.+]] = call ptr @g()
+; CHECK-NEXT: %[[addr2:.+]] = call ptr @llvm.coro.subfn.addr(ptr %[[hdl]], i8 0)
+; CHECK: musttail call fastcc void %[[addr2]](ptr %[[hdl]])
+; CHECK-NEXT: ret void
+; CHECK: %[[hdl2:.+]] = call ptr @h()
+; CHECK-NEXT: %[[addr3:.+]] = call ptr @llvm.coro.subfn.addr(ptr %[[hdl2]], i8 0)
+; CHECK: musttail call fastcc void %[[addr3]](ptr %[[hdl2]])
+; CHECK-NEXT: ret void
+; CHECK: %[[addr4:.+]] = call ptr @llvm.coro.subfn.addr(ptr null, i8 0)
+; CHECK: musttail call fastcc void %[[addr4]](ptr null)
+; CHECK-NEXT: ret void
+
+
+
+declare token @llvm.coro.id(i32, ptr readnone, ptr nocapture readonly, ptr) #1
+declare i1 @llvm.coro.alloc(token) #2
+declare i64 @llvm.coro.size.i64() #3
+declare ptr @llvm.coro.begin(token, ptr writeonly) #2
+declare token @llvm.coro.save(ptr) #2
+declare ptr @llvm.coro.frame() #3
+declare i8 @llvm.coro.suspend(token, i1) #2
+declare ptr @llvm.coro.free(token, ptr nocapture readonly) #1
+declare i1 @llvm.coro.end(ptr, i1, token) #2
+declare ptr @llvm.coro.subfn.addr(ptr nocapture readonly, i8) #1
+declare ptr @malloc(i64)
+declare i8 @switch_result()
+declare ptr @g()
+declare ptr @h()
+
+attributes #0 = { presplitcoroutine }
+attributes #1 = { argmemonly nounwind readonly }
+attributes #2 = { nounwind }
+attributes #3 = { nounwind readnone }

llvm/test/Instrumentation/InstrProfiling/Coro/coro-split-musttail10.ll

@@ -0,0 +1,55 @@
+; Tests that instrumentation doesn't interfere with lowering (coro-split).
+; It should convert coro.resume followed by a suspend to a musttail call.
+
+; RUN: opt < %s -passes='pgo-instr-gen,cgscc(coro-split),simplifycfg,early-cse' -S | FileCheck %s
+
+target triple = "wasm64-unknown-unknown"
+
+define void @f() #0 {
+entry:
+  %id = call token @llvm.coro.id(i32 0, ptr null, ptr null, ptr null)
+  %alloc = call ptr @malloc(i64 16) #3
+  %vFrame = call noalias nonnull ptr @llvm.coro.begin(token %id, ptr %alloc)
+
+  %save = call token @llvm.coro.save(ptr null)
+  %addr1 = call ptr @llvm.coro.subfn.addr(ptr null, i8 0)
+  call fastcc void %addr1(ptr 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(ptr null)
+  %addr2 = call ptr @llvm.coro.subfn.addr(ptr null, i8 0)
+  call fastcc void %addr2(ptr 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(ptr null, i1 false, token none)
+  ret void
+}
+
+; CHECK: musttail call
+
+declare token @llvm.coro.id(i32, ptr readnone, ptr nocapture readonly, ptr) #1
+declare i1 @llvm.coro.alloc(token) #2
+declare i64 @llvm.coro.size.i64() #3
+declare ptr @llvm.coro.begin(token, ptr writeonly) #2
+declare token @llvm.coro.save(ptr) #2
+declare ptr @llvm.coro.frame() #3
+declare i8 @llvm.coro.suspend(token, i1) #2
+declare ptr @llvm.coro.free(token, ptr nocapture readonly) #1
+declare i1 @llvm.coro.end(ptr, i1, token) #2
+declare ptr @llvm.coro.subfn.addr(ptr nocapture readonly, i8) #1
+declare ptr @malloc(i64)
+
+attributes #0 = { presplitcoroutine "target-features"="+tail-call" }
+attributes #1 = { argmemonly nounwind readonly }
+attributes #2 = { nounwind }
+attributes #3 = { nounwind readnone }

llvm/test/Instrumentation/InstrProfiling/Coro/coro-split-musttail11.ll

@@ -0,0 +1,55 @@
+; Tests that instrumentation doesn't interfere with lowering (coro-split).
+; It should convert coro.resume followed by a suspend to a musttail call.
+
+; RUN: opt < %s -passes='pgo-instr-gen,cgscc(coro-split),simplifycfg,early-cse' -S | FileCheck %s
+
+target triple = "wasm32-unknown-unknown"
+
+define void @f() #0 {
+entry:
+  %id = call token @llvm.coro.id(i32 0, ptr null, ptr null, ptr null)
+  %alloc = call ptr @malloc(i64 16) #3
+  %vFrame = call noalias nonnull ptr @llvm.coro.begin(token %id, ptr %alloc)
+
+  %save = call token @llvm.coro.save(ptr null)
+  %addr1 = call ptr @llvm.coro.subfn.addr(ptr null, i8 0)
+  call fastcc void %addr1(ptr 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(ptr null)
+  %addr2 = call ptr @llvm.coro.subfn.addr(ptr null, i8 0)
+  call fastcc void %addr2(ptr 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(ptr null, i1 false, token none)
+  ret void
+}
+
+; CHECK: musttail call
+
+declare token @llvm.coro.id(i32, ptr readnone, ptr nocapture readonly, ptr) #1
+declare i1 @llvm.coro.alloc(token) #2
+declare i64 @llvm.coro.size.i64() #3
+declare ptr @llvm.coro.begin(token, ptr writeonly) #2
+declare token @llvm.coro.save(ptr) #2
+declare ptr @llvm.coro.frame() #3
+declare i8 @llvm.coro.suspend(token, i1) #2
+declare ptr @llvm.coro.free(token, ptr nocapture readonly) #1
+declare i1 @llvm.coro.end(ptr, i1, token) #2
+declare ptr @llvm.coro.subfn.addr(ptr nocapture readonly, i8) #1
+declare ptr @malloc(i64)
+
+attributes #0 = { presplitcoroutine "target-features"="+tail-call" }
+attributes #1 = { argmemonly nounwind readonly }
+attributes #2 = { nounwind }
+attributes #3 = { nounwind readnone }