[llvm] r326394 - [DAE] don't remove args of musttail target/caller

[Reid Kleckner via llvm-commits]

Author: rnk
Date: Wed Feb 28 16:09:35 2018
New Revision: 326394

URL: http://llvm.org/viewvc/llvm-project?rev=326394&view=rev
Log:
[DAE] don't remove args of musttail target/caller

`musttail` requires identical signatures of caller and callee. Removing
arguments breaks `musttail` semantics.

PR36441

Patch by Fedor Indutny

Differential Revision: https://reviews.llvm.org/D43708

Added:
    llvm/trunk/test/Transforms/DeadArgElim/musttail-caller.ll
Modified:
    llvm/trunk/lib/Transforms/IPO/DeadArgumentElimination.cpp

Modified: llvm/trunk/lib/Transforms/IPO/DeadArgumentElimination.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/IPO/DeadArgumentElimination.cpp?rev=326394&r1=326393&r2=326394&view=diff
==============================================================================
--- llvm/trunk/lib/Transforms/IPO/DeadArgumentElimination.cpp (original)
+++ llvm/trunk/lib/Transforms/IPO/DeadArgumentElimination.cpp Wed Feb 28 16:09:35 2018
@@ -507,14 +507,28 @@ void DeadArgumentEliminationPass::Survey
   // MaybeLive. Initialized to a list of RetCount empty lists.
   RetUses MaybeLiveRetUses(RetCount);
 
-  for (Function::const_iterator BB = F.begin(), E = F.end(); BB != E; ++BB)
-    if (const ReturnInst *RI = dyn_cast<ReturnInst>(BB->getTerminator()))
+  bool HasMustTailCalls = false;
+
+  for (Function::const_iterator BB = F.begin(), E = F.end(); BB != E; ++BB) {
+    if (const ReturnInst *RI = dyn_cast<ReturnInst>(BB->getTerminator())) {
       if (RI->getNumOperands() != 0 && RI->getOperand(0)->getType()
           != F.getFunctionType()->getReturnType()) {
         // We don't support old style multiple return values.
         MarkLive(F);
         return;
       }
+    }
+
+    // If we have any returns of `musttail` results - the signature can't
+    // change
+    if (BB->getTerminatingMustTailCall() != nullptr)
+      HasMustTailCalls = true;
+  }
+
+  if (HasMustTailCalls) {
+    DEBUG(dbgs() << "DeadArgumentEliminationPass - " << F.getName()
+                 << " has musttail calls\n");
+  }
 
   if (!F.hasLocalLinkage() && (!ShouldHackArguments || F.isIntrinsic())) {
     MarkLive(F);
@@ -526,6 +540,9 @@ void DeadArgumentEliminationPass::Survey
   // Keep track of the number of live retvals, so we can skip checks once all
   // of them turn out to be live.
   unsigned NumLiveRetVals = 0;
+
+  bool HasMustTailCallers = false;
+
   // Loop all uses of the function.
   for (const Use &U : F.uses()) {
     // If the function is PASSED IN as an argument, its address has been
@@ -536,6 +553,11 @@ void DeadArgumentEliminationPass::Survey
       return;
     }
 
+    // The number of arguments for `musttail` call must match the number of
+    // arguments of the caller
+    if (CS.isMustTailCall())
+      HasMustTailCallers = true;
+
     // If this use is anything other than a call site, the function is alive.
     const Instruction *TheCall = CS.getInstruction();
     if (!TheCall) {   // Not a direct call site?
@@ -580,6 +602,11 @@ void DeadArgumentEliminationPass::Survey
     }
   }
 
+  if (HasMustTailCallers) {
+    DEBUG(dbgs() << "DeadArgumentEliminationPass - " << F.getName()
+                 << " has musttail callers\n");
+  }
+
   // Now we've inspected all callers, record the liveness of our return values.
   for (unsigned i = 0; i != RetCount; ++i)
     MarkValue(CreateRet(&F, i), RetValLiveness[i], MaybeLiveRetUses[i]);
@@ -593,12 +620,19 @@ void DeadArgumentEliminationPass::Survey
   for (Function::const_arg_iterator AI = F.arg_begin(),
        E = F.arg_end(); AI != E; ++AI, ++i) {
     Liveness Result;
-    if (F.getFunctionType()->isVarArg()) {
+    if (F.getFunctionType()->isVarArg() || HasMustTailCallers ||
+        HasMustTailCalls) {
       // Variadic functions will already have a va_arg function expanded inside
       // them, making them potentially very sensitive to ABI changes resulting
       // from removing arguments entirely, so don't. For example AArch64 handles
       // register and stack HFAs very differently, and this is reflected in the
       // IR which has already been generated.
+      //
+      // `musttail` calls to this function restrict argument removal attempts.
+      // The signature of the caller must match the signature of the function.
+      //
+      // `musttail` calls in this function prevents us from changing its
+      // signature
       Result = Live;
     } else {
       // See what the effect of this use is (recording any uses that cause

Added: llvm/trunk/test/Transforms/DeadArgElim/musttail-caller.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/DeadArgElim/musttail-caller.ll?rev=326394&view=auto
==============================================================================
--- llvm/trunk/test/Transforms/DeadArgElim/musttail-caller.ll (added)
+++ llvm/trunk/test/Transforms/DeadArgElim/musttail-caller.ll Wed Feb 28 16:09:35 2018
@@ -0,0 +1,16 @@
+; RUN: opt -deadargelim -S < %s | FileCheck %s
+; PR36441
+; Dead arguments should not be removed in presence of `musttail` calls.
+
+; CHECK-LABEL: define internal void @test(i32 %a, i32 %b)
+; CHECK: musttail call void @foo(i32 %a, i32 0)
+; FIXME: we should replace those with `undef`s
+define internal void @test(i32 %a, i32 %b) {
+  musttail call void @foo(i32 %a, i32 0)
+  ret void
+}
+
+; CHECK-LABEL: define internal void @foo(i32 %a, i32 %b)
+define internal void @foo(i32 %a, i32 %b) {
+  ret void
+}