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

diff --git a/lib/CodeGen/StackColoring.cpp b/lib/CodeGen/StackColoring.cpp
index a14d730025f506cd95558c320880f09f76a6cddf..1a7801abd8a12da9eb4a9902f5136645fe5e1398 100644 (file)
--- 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();

diff --git a/test/CodeGen/X86/StackColoring.ll b/test/CodeGen/X86/StackColoring.ll
index a83a4ebbe2edd63bee23ce0e9ca4308e2b58b417..f8ae74f292d224b51b7aaee128dba208cea50ec6 100644 (file)
--- a/test/CodeGen/X86/StackColoring.ll
+++ b/test/CodeGen/X86/StackColoring.ll
@@ -376,6 +376,30 @@ block2:
 }
 
 
+; Check that we don't assert and crash even when there are usages
+; of allocas which do not read or write outside the declared lifetime regions.
+;YESCOLOR: shady_range
+;NOCOLOR:  shady_range
+
+%struct.Klass = type { i32, i32 }
+
+define i32 @shady_range(i32 %argc, i8** nocapture %argv) uwtable {
+  %a.i = alloca [4 x %struct.Klass], align 16
+  %b.i = alloca [4 x %struct.Klass], align 16
+  %a8 = bitcast [4 x %struct.Klass]* %a.i to i8*
+  %b8 = bitcast [4 x %struct.Klass]* %b.i to i8*
+  ; I am used outside the lifetime zone below:
+  %z2 = getelementptr inbounds [4 x %struct.Klass]* %a.i, i64 0, i64 0, i32 0
+  call void @llvm.lifetime.start(i64 -1, i8* %a8)
+  call void @llvm.lifetime.start(i64 -1, i8* %b8)
+  %z3 = load i32* %z2, align 16
+  %r = call i32 @foo(i32 %z3, i8* %a8)
+  %r2 = call i32 @foo(i32 %z3, i8* %b8)
+  call void @llvm.lifetime.end(i64 -1, i8* %a8)
+  call void @llvm.lifetime.end(i64 -1, i8* %b8)
+  ret i32 9
+}
+
 declare void @bar([100 x i32]* , [100 x i32]*) nounwind
 
 declare void @llvm.lifetime.start(i64, i8* nocapture) nounwind