Stack Coloring: We have code that checks that all of the uses of allocas

are within the lifetime zone. Sometime legitimate usages of allocas are
hoisted outside of the lifetime zone. For example, GEPS may calculate the
address of a member of an allocated struct. This commit makes sure that
we only check (abort regions or assert) for instructions that read and write
memory using stack frames directly. Notice that by allowing legitimate
usages outside the lifetime zone we also stop checking for instructions
which use derivatives of allocas. We will catch less bugs in user code
and in the compiler itself.



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@163791 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 17 insertions, 5 deletions

diff --git a/lib/CodeGen/StackColoring.cpp b/lib/CodeGen/StackColoring.cpp
index a14d730025..1a7801abd8 100644
--- a/lib/CodeGen/StackColoring.cpp
+++ b/lib/CodeGen/StackColoring.cpp
@@ -73,7 +73,6 @@ STATISTIC(StackSlotMerged, "Number of stack slot merged.");
 STATISTIC(EscapedAllocas,
           "Number of allocas that escaped the lifetime region");
 
-
 //===----------------------------------------------------------------------===//
 //                           StackColoring Pass
 //===----------------------------------------------------------------------===//
@@ -259,8 +258,8 @@ unsigned StackColoring::collectMarkers(unsigned NumSlot) {
 
       const Value *Allocation = MFI->getObjectAllocation(Slot);
       if (Allocation) {
-        DEBUG(dbgs()<<"Found lifetime marker for allocation: "<<
-              Allocation->getName()<<"\n");
+        DEBUG(dbgs()<<"Found a lifetime marker for slot #"<<Slot<<
+              " with allocation: "<< Allocation->getName()<<"\n");
       }
 
       if (IsStart) {
@@ -538,8 +537,12 @@ void StackColoring::remapInstructions(DenseMap<int, int> &SlotRemap) {
         // inside the expected live range. If the instruction is not inside
         // the calculated range then it means that the alloca usage moved
         // outside of the lifetime markers.
+        // NOTE: Alloca address calculations which happen outside the lifetime
+        // zone are are okay, despite the fact that we don't have a good way
+        // for validating all of the usages of the calculation.
 #ifndef NDEBUG
-        if (!I->isDebugValue()) {
+        bool TouchesMemory = I->mayLoad() || I->mayStore();
+        if (!I->isDebugValue() && TouchesMemory) {
           SlotIndex Index = Indexes->getInstructionIndex(I);
           LiveInterval *Interval = Intervals[FromSlot];
           assert(Interval->find(Index) != Interval->end() &&
@@ -569,6 +572,15 @@ void StackColoring::removeInvalidSlotRanges() {
           I->getOpcode() == TargetOpcode::LIFETIME_END || I->isDebugValue())
         continue;
 
+      // Some intervals are suspicious! In some cases we find address
+      // calculations outside of the lifetime zone, but not actual memory
+      // read or write. Memory accesses outside of the lifetime zone are a clear
+      // violation, but address calculations are okay. This can happen when
+      // GEPs are hoisted outside of the lifetime zone.
+      // So, in here we only check instrucitons which can read or write memory.
+      if (!I->mayLoad() && !I->mayStore())
+        continue;
+
       // Check all of the machine operands.
       for (unsigned i = 0 ; i <  I->getNumOperands(); ++i) {
         MachineOperand &MO = I->getOperand(i);
@@ -652,7 +664,7 @@ bool StackColoring::runOnMachineFunction(MachineFunction &Func) {
   DEBUG(dbgs()<<"Total Stack size: "<<TotalSize<<" bytes\n\n");
 
   // Don't continue because there are not enough lifetime markers, or the
-  // stack or too small, or we are told not to optimize the slots.
+  // stack is too small, or we are told not to optimize the slots.
   if (NumMarkers < 2 || TotalSize < 16 || DisableColoring) {
     DEBUG(dbgs()<<"Will not try to merge slots.\n");
     return removeAllMarkers();