[PATCH] D145209: [DAE] Don't DAE if we musttail call a "live" (non-DAE-able) function

[Mircea Trofin via Phabricator via llvm-commits]

mtrofin updated this revision to Diff 502192.
mtrofin added a comment.

<eyeroll>


Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D145209/new/

https://reviews.llvm.org/D145209

Files:
  llvm/include/llvm/Transforms/IPO/DeadArgumentElimination.h
  llvm/lib/Transforms/IPO/DeadArgumentElimination.cpp
  llvm/test/Transforms/DeadArgElim/musttail-indirect.ll


Index: llvm/test/Transforms/DeadArgElim/musttail-indirect.ll
===================================================================
--- /dev/null
+++ llvm/test/Transforms/DeadArgElim/musttail-indirect.ll
@@ -0,0 +1,26 @@
+; RUN: opt -passes=deadargelim,verify -S < %s 2>&1 | FileCheck %s
+define internal i32 @test_caller(ptr %fptr, i32 %a, i32 %b) {
+  %r = musttail call i32 @test(ptr %fptr, i32 %a, i32 %b)
+  ret i32 %r
+}
+
+define internal i32 @test(ptr %fptr, i32 %a, i32 %b) {
+  %r = musttail call i32 %fptr(ptr %fptr, i32 %a, i32 0)
+  ret i32 %r
+}
+
+define internal i32 @direct_test() {
+  %r = musttail call i32 @foo()
+  ret i32 %r
+}
+
+declare i32 @foo()
+
+; CHECK-NOT: cannot guarantee tail call due to mismatched parameter counts
+
+; CHECK: define internal i32 @test_caller
+; CHECK-NEXT: %r = musttail call i32 @test
+
+; CHECK: define internal i32 @test
+; CHECK-NEXT: %r = musttail call i32 %fptr
+
Index: llvm/lib/Transforms/IPO/DeadArgumentElimination.cpp
===================================================================
--- llvm/lib/Transforms/IPO/DeadArgumentElimination.cpp
+++ llvm/lib/Transforms/IPO/DeadArgumentElimination.cpp
@@ -520,8 +520,15 @@
   for (const BasicBlock &BB : F) {
     // If we have any returns of `musttail` results - the signature can't
     // change
-    if (BB.getTerminatingMustTailCall() != nullptr)
+    if (const auto *TC = BB.getTerminatingMustTailCall()) {
       HasMustTailCalls = true;
+      // In addition, if the called function is virtual, we can't change
+      // the return type.
+      if (!TC->getCalledFunction()) {
+        markLive(F);
+        return;
+      }
+    }
   }
 
   if (HasMustTailCalls) {
@@ -1081,6 +1088,25 @@
   return true;
 }
 
+void DeadArgumentEliminationPass::propagateVirtMustcallLiveness(
+    const Module &M) {
+  // If a function was marked "live", and it has musttail callers, they in turn
+  // can't change either.
+  LiveFuncSet NewLiveFuncs(LiveFunctions);
+  while (!NewLiveFuncs.empty()) {
+    LiveFuncSet Temp;
+    for (const auto *F : NewLiveFuncs)
+      for (const auto *U : F->users())
+        if (const auto *CB = dyn_cast<CallBase>(U))
+          if (CB->isMustTailCall())
+            Temp.insert(CB->getParent()->getParent());
+    NewLiveFuncs.clear();
+    NewLiveFuncs.insert(Temp.begin(), Temp.end());
+    for (const auto *F : Temp)
+      markLive(*F);
+  }
+}
+
 PreservedAnalyses DeadArgumentEliminationPass::run(Module &M,
                                                    ModuleAnalysisManager &) {
   bool Changed = false;
@@ -1101,6 +1127,8 @@
   for (auto &F : M)
     surveyFunction(F);
 
+  propagateVirtMustcallLiveness(M);
+
   // Now, remove all dead arguments and return values from each function in
   // turn.  We use make_early_inc_range here because functions will probably get
   // removed (i.e. replaced by new ones).
Index: llvm/include/llvm/Transforms/IPO/DeadArgumentElimination.h
===================================================================
--- llvm/include/llvm/Transforms/IPO/DeadArgumentElimination.h
+++ llvm/include/llvm/Transforms/IPO/DeadArgumentElimination.h
@@ -136,6 +136,7 @@
   bool removeDeadStuffFromFunction(Function *F);
   bool deleteDeadVarargs(Function &F);
   bool removeDeadArgumentsFromCallers(Function &F);
+  void propagateVirtMustcallLiveness(const Module &M);
 };
 
 } // end namespace llvm


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