[Coroutines] Remove corresponding phi values when apply simplifyTermi…

…natorLeadingToRet

Summary:
In addMustTailToCoroResumes, we set musttail on those resume instructions that are followed by a ret instruction. This is done by simplifyTerminatorLeadingToRet which replace a sequence of branches leading to a ret with a clone of the ret.

However it forgets to remove corresponding PHI values that come from basic block of replaced branch, and may cause jumpthreading pass hangs (https://bugs.llvm.org/show_bug.cgi?id=43720)

This patch fix this issue

Test Plan:
cppcoro library with O3+flto
check-llvm

Reviewers: modocache, GorNishanov, lewissbaker

Reviewed By: modocache

Subscribers: mehdi_amini, EricWF, hiraditya, dexonsmith, jfb, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D71826

Patch by junparser (JunMa)!

llvm/lib/Transforms/Coroutines/CoroSplit.cpp

@@ -908,17 +908,29 @@ scanPHIsAndUpdateValueMap(Instruction *Prev, BasicBlock *NewBlock,
 // values and select the correct case successor when possible.
 static bool simplifyTerminatorLeadingToRet(Instruction *InitialInst) {
   DenseMap<Value *, Value *> ResolvedValues;
+  BasicBlock *UnconditionalSucc = nullptr;
 
   Instruction *I = InitialInst;
   while (I->isTerminator()) {
     if (isa<ReturnInst>(I)) {
-      if (I != InitialInst)
+      if (I != InitialInst) {
+        // If InitialInst is an unconditional branch,
+        // remove PHI values that come from basic block of InitialInst
+        if (UnconditionalSucc)
+          for (PHINode &PN : UnconditionalSucc->phis()) {
+            int idx = PN.getBasicBlockIndex(InitialInst->getParent());
+            if (idx != -1)
+              PN.removeIncomingValue(idx);
+          }
         ReplaceInstWithInst(InitialInst, I->clone());
+      }
       return true;
     }
     if (auto *BR = dyn_cast<BranchInst>(I)) {
       if (BR->isUnconditional()) {
         BasicBlock *BB = BR->getSuccessor(0);
+        if (I == InitialInst)
+          UnconditionalSucc = BB;
         scanPHIsAndUpdateValueMap(I, BB, ResolvedValues);
         I = BB->getFirstNonPHIOrDbgOrLifetime();
         continue;

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

@@ -2,7 +2,7 @@
 ; musttail call.
 ; RUN: opt < %s -coro-split -S | FileCheck %s
 
-define void @f() "coroutine.presplit"="1" {
+define void @f() #0 {
 entry:
   %id = call token @llvm.coro.id(i32 0, i8* null, i8* null, i8* null)
   %alloc = call i8* @malloc(i64 16) #3
@@ -47,14 +47,19 @@ exit:
 ; CHECK-NEXT: musttail call fastcc void %[[pv2]](i8* null)
 ; CHECK-NEXT: ret void
 
-declare token @llvm.coro.id(i32, i8* readnone, i8* nocapture readonly, i8*)
-declare i1 @llvm.coro.alloc(token) #3
-declare i64 @llvm.coro.size.i64() #5
-declare i8* @llvm.coro.begin(token, i8* writeonly) #3
-declare token @llvm.coro.save(i8*) #3
-declare i8* @llvm.coro.frame() #5
-declare i8 @llvm.coro.suspend(token, i1) #3
-declare i8* @llvm.coro.free(token, i8* nocapture readonly) #2
-declare i1 @llvm.coro.end(i8*, i1) #3
-declare i8* @llvm.coro.subfn.addr(i8* nocapture readonly, i8) #5
+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 }

llvm/test/Transforms/Coroutines/coro-split-musttail1.ll

@@ -0,0 +1,104 @@
+; Tests that coro-split will convert coro.resume followed by a suspend to a
+; musttail call.
+; RUN: opt < %s -coro-split -S | FileCheck %s
+
+define void @f() #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)
+  %addr1 = call i8* @llvm.coro.subfn.addr(i8* null, i8 0)
+  %pv1 = bitcast i8* %addr1 to void (i8*)*
+  call fastcc void %pv1(i8* 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(i8* 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 i8* @g()
+  %addr2 = call i8* @llvm.coro.subfn.addr(i8* %hdl, i8 0)
+  %pv2 = bitcast i8* %addr2 to void (i8*)*
+  call fastcc void %pv2(i8* %hdl)
+  br label %final.suspend
+await.resume2:
+  %hdl2 = call i8* @h()
+  %addr3 = call i8* @llvm.coro.subfn.addr(i8* %hdl2, i8 0)
+  %pv3 = bitcast i8* %addr3 to void (i8*)*
+  call fastcc void %pv3(i8* %hdl2)
+  br label %final.suspend
+await.resume3:
+  %addr4 = call i8* @llvm.coro.subfn.addr(i8* null, i8 0)
+  %pv4 = bitcast i8* %addr4 to void (i8*)*
+  call fastcc void %pv4(i8* 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(i8* null, i1 false)
+  ret void
+unreach:
+  unreachable
+}
+
+; Verify that in the initial function resume is not marked with musttail.
+; CHECK-LABEL: @f(
+; CHECK: %[[addr1:.+]] = call i8* @llvm.coro.subfn.addr(i8* null, i8 0)
+; CHECK-NEXT: %[[pv1:.+]] = bitcast i8* %[[addr1]] to void (i8*)*
+; CHECK-NOT: musttail call fastcc void %[[pv1]](i8* null)
+
+; Verify that in the resume part resume call is marked with musttail.
+; CHECK-LABEL: @f.resume(
+; CHECK: %[[hdl:.+]] = call i8* @g()
+; CHECK-NEXT: %[[addr2:.+]] = call i8* @llvm.coro.subfn.addr(i8* %[[hdl]], i8 0)
+; CHECK-NEXT: %[[pv2:.+]] = bitcast i8* %[[addr2]] to void (i8*)*
+; CHECK-NEXT: musttail call fastcc void %[[pv2]](i8* %[[hdl]])
+; CHECK-NEXT: ret void
+; CHECK: %[[hdl2:.+]] = call i8* @h()
+; CHECK-NEXT: %[[addr3:.+]] = call i8* @llvm.coro.subfn.addr(i8* %[[hdl2]], i8 0)
+; CHECK-NEXT: %[[pv3:.+]] = bitcast i8* %[[addr3]] to void (i8*)*
+; CHECK-NEXT: musttail call fastcc void %[[pv3]](i8* %[[hdl2]])
+; CHECK-NEXT: ret void
+; CHECK: %[[addr4:.+]] = call i8* @llvm.coro.subfn.addr(i8* null, i8 0)
+; CHECK-NEXT: %[[pv4:.+]] = bitcast i8* %[[addr4]] to void (i8*)*
+; CHECK-NEXT: musttail call fastcc void %[[pv4]](i8* 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)
+declare i8 @switch_result()
+declare i8* @g()
+declare i8* @h()
+
+attributes #0 = { "coroutine.presplit"="1" }
+attributes #1 = { argmemonly nounwind readonly }
+attributes #2 = { nounwind }
+attributes #3 = { nounwind readnone }