Widen EHScope::ClenupBitFields::FixupDepth to avoid overflowing it (P…

…R23490)

It currently only takes 2048 gotos to overflow the FixupDepth bitfield,
causing silent miscompilation. Apparently some parser generators run into
this (see PR).

I don't know that that data structure is terribly size sensitive anyway,
and since there's no room to widen the bitfield, let's just use a separate
word in EHCatchScope for it.

Differential Revision: http://reviews.llvm.org/D21566

llvm-svn: 273434

clang/lib/CodeGen/CGCleanup.h

@@ -86,11 +86,6 @@ class EHScope {
     /// The amount of extra storage needed by the Cleanup.
     /// Always a multiple of the scope-stack alignment.
     unsigned CleanupSize : 12;
-
-    /// The number of fixups required by enclosing scopes (not including
-    /// this one).  If this is the top cleanup scope, all the fixups
-    /// from this index onwards belong to this scope.
-    unsigned FixupDepth : 32 - 18 - NumCommonBits; // currently 12
   };
 
   class FilterBitFields {
@@ -188,6 +183,7 @@ class EHCatchScope : public EHScope {
                EHScopeStack::stable_iterator enclosingEHScope)
     : EHScope(Catch, enclosingEHScope) {
     CatchBits.NumHandlers = numHandlers;
+    assert(CatchBits.NumHandlers == numHandlers && "NumHandlers overflow?");
   }
 
   unsigned getNumHandlers() const {
@@ -263,6 +259,11 @@ class LLVM_ALIGNAS(/*alignof(uint64_t)*/ 8) EHCleanupScope : public EHScope {
   };
   mutable struct ExtInfo *ExtInfo;
 
+  /// The number of fixups required by enclosing scopes (not including
+  /// this one).  If this is the top cleanup scope, all the fixups
+  /// from this index onwards belong to this scope.
+  unsigned FixupDepth;
+
   struct ExtInfo &getExtInfo() {
     if (!ExtInfo) ExtInfo = new struct ExtInfo();
     return *ExtInfo;
@@ -288,16 +289,16 @@ class LLVM_ALIGNAS(/*alignof(uint64_t)*/ 8) EHCleanupScope : public EHScope {
                  unsigned cleanupSize, unsigned fixupDepth,
                  EHScopeStack::stable_iterator enclosingNormal,
                  EHScopeStack::stable_iterator enclosingEH)
-    : EHScope(EHScope::Cleanup, enclosingEH), EnclosingNormal(enclosingNormal),
-      NormalBlock(nullptr), ActiveFlag(nullptr), ExtInfo(nullptr) {
+      : EHScope(EHScope::Cleanup, enclosingEH),
+        EnclosingNormal(enclosingNormal), NormalBlock(nullptr),
+        ActiveFlag(nullptr), ExtInfo(nullptr), FixupDepth(fixupDepth) {
     CleanupBits.IsNormalCleanup = isNormal;
     CleanupBits.IsEHCleanup = isEH;
     CleanupBits.IsActive = isActive;
     CleanupBits.IsLifetimeMarker = false;
     CleanupBits.TestFlagInNormalCleanup = false;
     CleanupBits.TestFlagInEHCleanup = false;
     CleanupBits.CleanupSize = cleanupSize;
-    CleanupBits.FixupDepth = fixupDepth;
 
     assert(CleanupBits.CleanupSize == cleanupSize && "cleanup size overflow");
   }
@@ -343,7 +344,7 @@ class LLVM_ALIGNAS(/*alignof(uint64_t)*/ 8) EHCleanupScope : public EHScope {
     return CleanupBits.TestFlagInEHCleanup;
   }
 
-  unsigned getFixupDepth() const { return CleanupBits.FixupDepth; }
+  unsigned getFixupDepth() const { return FixupDepth; }
   EHScopeStack::stable_iterator getEnclosingNormalCleanup() const {
     return EnclosingNormal;
   }
@@ -451,6 +452,7 @@ class EHFilterScope : public EHScope {
   EHFilterScope(unsigned numFilters)
     : EHScope(Filter, EHScopeStack::stable_end()) {
     FilterBits.NumFilters = numFilters;
+    assert(FilterBits.NumFilters == numFilters && "NumFilters overflow");
   }
 
   static size_t getSizeForNumFilters(unsigned numFilters) {

clang/test/CodeGen/fixup-depth-overflow.c

@@ -0,0 +1,26 @@
+// RUN: %clang_cc1 -O1 -disable-llvm-optzns -emit-llvm -o - %s | FileCheck %s
+
+#define M if (x) goto L1;
+#define M10 M M M M M M M M M M
+#define M100 M10 M10 M10 M10 M10 M10 M10 M10 M10 M10
+#define M1000 M100 M100 M100 M100 M100 M100 M100 M100 M100 M100
+
+void f(int x) {
+  int h;
+
+  // Many gotos to not-yet-emitted labels would cause EHScope's FixupDepth
+  // to overflow (PR23490).
+  M1000 M1000 M1000
+
+  if (x == 5) {
+    // This will cause us to emit a clean-up of the stack variable. If the
+    // FixupDepths are broken, fixups will erroneously get threaded through it.
+    int i;
+  }
+
+L1:
+  return;
+}
+
+// CHECK-LABEL: define void @f
+// CHECK-NOT: cleanup