[llvm] r366998 - [IPSCCP] Add assertion to surface cases where we zap returns with overdefined users.

[Florian Hahn via llvm-commits]

Author: fhahn
Date: Thu Jul 25 02:37:09 2019
New Revision: 366998

URL: http://llvm.org/viewvc/llvm-project?rev=366998&view=rev
Log:
[IPSCCP] Add assertion to surface cases where we zap returns with overdefined users.

We should only zap returns in functions, where all live users have a
replace-able value (are not overdefined). Unused return values should be
undefined.

This should make it easier to detect bugs like in PR42738.

Alternatively we could bail out of zapping the function returns, but I
think it would be better to address those divergences between function
and call-site values where they are actually caused.

Reviewers: davide, efriedma

Reviewed By: davide, efriedma

Differential Revision: https://reviews.llvm.org/D65222

Modified:
    llvm/trunk/lib/Transforms/Scalar/SCCP.cpp

Modified: llvm/trunk/lib/Transforms/Scalar/SCCP.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/Scalar/SCCP.cpp?rev=366998&r1=366997&r2=366998&view=diff
==============================================================================
--- llvm/trunk/lib/Transforms/Scalar/SCCP.cpp (original)
+++ llvm/trunk/lib/Transforms/Scalar/SCCP.cpp Thu Jul 25 02:37:09 2019
@@ -1924,6 +1924,21 @@ static void findReturnsToZap(Function &F
     return;
   }
 
+  assert(
+      all_of(F.users(),
+             [&Solver](User *U) {
+               if (isa<Instruction>(U) &&
+                   !Solver.isBlockExecutable(cast<Instruction>(U)->getParent()))
+                 return false;
+               if (U->getType()->isStructTy()) {
+                 return all_of(
+                     Solver.getStructLatticeValueFor(U),
+                     [](const LatticeVal &LV) { return !LV.isOverdefined(); });
+               }
+               return !Solver.getLatticeValueFor(U).isOverdefined();
+             }) &&
+      "We can only zap functions where all live users have a concrete value");
+
   for (BasicBlock &BB : F) {
     if (CallInst *CI = BB.getTerminatingMustTailCall()) {
       LLVM_DEBUG(dbgs() << "Can't zap return of the block due to present "