Merging r373216:

------------------------------------------------------------------------
r373216 | probinson | 2019-09-30 08:01:35 -0700 (Mon, 30 Sep 2019) | 7 lines

[SSP] [1/3] Revert "StackProtector: Use PointerMayBeCaptured"
"Captured" and "relevant to Stack Protector" are not the same thing.

This reverts commit f29366b.
aka r363169.

Differential Revision: https://reviews.llvm.org/D67842
------------------------------------------------------------------------

To avoid changing the ABI, the VisitedPHIs member from the StackProtector class
was replaced with a local variable in StackProtector::RequiresStackProtector().

Author: pogo59

llvm/include/llvm/CodeGen/StackProtector.h

@@ -89,7 +89,8 @@ class StackProtector : public FunctionPass {
                                 bool InStruct = false) const;
 
   /// Check whether a stack allocation has its address taken.
-  bool HasAddressTaken(const Instruction *AI);
+  bool HasAddressTaken(const Instruction *AI,
+                       SmallPtrSetImpl<const PHINode *> &VisitedPHIs);
 
   /// RequiresStackProtector - Check whether or not this function needs a
   /// stack protector based upon the stack protector level.

llvm/lib/CodeGen/StackProtector.cpp

@@ -17,7 +17,6 @@
 #include "llvm/ADT/SmallPtrSet.h"
 #include "llvm/ADT/Statistic.h"
 #include "llvm/Analysis/BranchProbabilityInfo.h"
-#include "llvm/Analysis/CaptureTracking.h"
 #include "llvm/Analysis/EHPersonalities.h"
 #include "llvm/Analysis/OptimizationRemarkEmitter.h"
 #include "llvm/CodeGen/Passes.h"
@@ -157,6 +156,41 @@ bool StackProtector::ContainsProtectableArray(Type *Ty, bool &IsLarge,
   return NeedsProtector;
 }
 
+bool StackProtector::HasAddressTaken(const Instruction *AI,
+                                SmallPtrSetImpl<const PHINode *> &VisitedPHIs) {
+  for (const User *U : AI->users()) {
+    if (const StoreInst *SI = dyn_cast<StoreInst>(U)) {
+      if (AI == SI->getValueOperand())
+        return true;
+    } else if (const PtrToIntInst *SI = dyn_cast<PtrToIntInst>(U)) {
+      if (AI == SI->getOperand(0))
+        return true;
+    } else if (const CallInst *CI = dyn_cast<CallInst>(U)) {
+      // Ignore intrinsics that are not calls. TODO: Use isLoweredToCall().
+      if (!isa<DbgInfoIntrinsic>(CI) && !CI->isLifetimeStartOrEnd())
+        return true;
+    } else if (isa<InvokeInst>(U)) {
+      return true;
+    } else if (const SelectInst *SI = dyn_cast<SelectInst>(U)) {
+      if (HasAddressTaken(SI, VisitedPHIs))
+        return true;
+    } else if (const PHINode *PN = dyn_cast<PHINode>(U)) {
+      // Keep track of what PHI nodes we have already visited to ensure
+      // they are only visited once.
+      if (VisitedPHIs.insert(PN).second)
+        if (HasAddressTaken(PN, VisitedPHIs))
+          return true;
+    } else if (const GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(U)) {
+      if (HasAddressTaken(GEP, VisitedPHIs))
+        return true;
+    } else if (const BitCastInst *BI = dyn_cast<BitCastInst>(U)) {
+      if (HasAddressTaken(BI, VisitedPHIs))
+        return true;
+    }
+  }
+  return false;
+}
+
 /// Search for the first call to the llvm.stackprotector intrinsic and return it
 /// if present.
 static const CallInst *findStackProtectorIntrinsic(Function &F) {
@@ -211,6 +245,12 @@ bool StackProtector::RequiresStackProtector() {
   else if (!F->hasFnAttribute(Attribute::StackProtect))
     return false;
 
+  /// VisitedPHIs - The set of PHI nodes visited when determining
+  /// if a variable's reference has been taken.  This set
+  /// is maintained to ensure we don't visit the same PHI node multiple
+  /// times.
+  SmallPtrSet<const PHINode *, 16> VisitedPHIs;
+
   for (const BasicBlock &BB : *F) {
     for (const Instruction &I : BB) {
       if (const AllocaInst *AI = dyn_cast<AllocaInst>(&I)) {
@@ -264,9 +304,7 @@ bool StackProtector::RequiresStackProtector() {
           continue;
         }
 
-        if (Strong && PointerMayBeCaptured(AI,
-                                           /* ReturnCaptures */ false,
-                                           /* StoreCaptures */ true)) {
+        if (Strong && HasAddressTaken(AI, VisitedPHIs)) {
           ++NumAddrTaken;
           Layout.insert(std::make_pair(AI, MachineFrameInfo::SSPLK_AddrOf));
           ORE.emit([&]() {

llvm/test/CodeGen/X86/stack-protector.ll

@@ -4087,8 +4087,8 @@ define i32 @IgnoreIntrinsicTest() #1 {
   %1 = alloca i32, align 4
   %2 = bitcast i32* %1 to i8*
   call void @llvm.lifetime.start.p0i8(i64 4, i8* nonnull %2)
-  store i32 1, i32* %1, align 4
-  %3 = load i32, i32* %1, align 4
+  store volatile i32 1, i32* %1, align 4
+  %3 = load volatile i32, i32* %1, align 4
   %4 = mul nsw i32 %3, 42
   call void @llvm.lifetime.end.p0i8(i64 4, i8* nonnull %2)
   ret i32 %4

llvm/test/Transforms/StackProtector/X86/captures.ll

@@ -523,7 +523,6 @@ int main(int argc, char **argv) {
   initializeDwarfEHPreparePass(Registry);
   initializeSafeStackLegacyPassPass(Registry);
   initializeSjLjEHPreparePass(Registry);
-  initializeStackProtectorPass(Registry);
   initializePreISelIntrinsicLoweringLegacyPassPass(Registry);
   initializeGlobalMergePass(Registry);
   initializeIndirectBrExpandPassPass(Registry);