From 79782fc8649e081b59fe2f96265042eaec1542a7 Mon Sep 17 00:00:00 2001
From: Eli Friedman <eli.friedman@gmail.com>
Date: Tue, 20 Sep 2011 23:28:51 +0000
Subject: Make sure IPSCCP never marks a tracked call as overdefined in
 SCCPSolver::ResolvedUndefsIn.  If we do, we can end up in a situation where a
 function is resolved to return a constant, but the caller is marked
 overdefined, which confuses the code later.

<rdar://problem/9956541> (again).



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@140210 91177308-0d34-0410-b5e6-96231b3b80d8
---
 lib/Transforms/Scalar/SCCP.cpp | 44 +++++++++++++++++++++++++++++++++---------
 1 file changed, 35 insertions(+), 9 deletions(-)

(limited to 'lib/Transforms/Scalar/SCCP.cpp')

diff --git a/lib/Transforms/Scalar/SCCP.cpp b/lib/Transforms/Scalar/SCCP.cpp
index 02e6b72d3a..196a847fc0 100644
--- a/lib/Transforms/Scalar/SCCP.cpp
+++ b/lib/Transforms/Scalar/SCCP.cpp
@@ -1433,15 +1433,25 @@ bool SCCPSolver::ResolvedUndefsIn(Function &F) {
       if (I->getType()->isVoidTy()) continue;
       
       if (StructType *STy = dyn_cast<StructType>(I->getType())) {
-        // Only a few things that can be structs matter for undef.  Just send
-        // all their results to overdefined.  We could be more precise than this
-        // but it isn't worth bothering.
-        if (!isa<ExtractValueInst>(I) && !isa<InsertValueInst>(I)) {
-          for (unsigned i = 0, e = STy->getNumElements(); i != e; ++i) {
-            LatticeVal &LV = getStructValueState(I, i);
-            if (LV.isUndefined())
-              markOverdefined(LV, I);
-          }
+        // Only a few things that can be structs matter for undef.
+
+        // Tracked calls must never be marked overdefined in ResolvedUndefsIn.
+        if (CallSite CS = CallSite(I))
+          if (Function *F = CS.getCalledFunction())
+            if (MRVFunctionsTracked.count(F))
+              continue;
+
+        // extractvalue and insertvalue don't need to be marked; they are
+        // tracked as precisely as their operands. 
+        if (isa<ExtractValueInst>(I) || isa<InsertValueInst>(I))
+          continue;
+
+        // Send the results of everything else to overdefined.  We could be
+        // more precise than this but it isn't worth bothering.
+        for (unsigned i = 0, e = STy->getNumElements(); i != e; ++i) {
+          LatticeVal &LV = getStructValueState(I, i);
+          if (LV.isUndefined())
+            markOverdefined(LV, I);
         }
         continue;
       }
@@ -1594,6 +1604,22 @@ bool SCCPSolver::ResolvedUndefsIn(Function &F) {
           break;
         markOverdefined(I);
         return true;
+      case Instruction::Call:
+      case Instruction::Invoke: {
+        // There are two reasons a call can have an undef result
+        // 1. It could be tracked.
+        // 2. It could be constant-foldable.
+        // Because of the way we solve return values, tracked calls must
+        // never be marked overdefined in ResolvedUndefsIn.
+        if (Function *F = CallSite(I).getCalledFunction())
+          if (TrackedRetVals.count(F))
+            break;
+
+        // If the call is constant-foldable, we mark it overdefined because
+        // we do not know what return values are valid.
+        markOverdefined(I);
+        return true;
+      }
       default:
         // If we don't know what should happen here, conservatively mark it
         // overdefined.
-- 
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