PNaCl: Remove and disallow llvm.invariant.start/end intrinsics

These markers work in a similar way to llvm.lifetime.start/end, so we
should remove them for similar reasons: it's not very well defined how
one marker cancels out the effects of the other.

Arguably, invariant.start/end are less useful than lifetime.start/end.
They are ignored by the backend.  They are generated in fewer places:
invariant.start is generated by Clang (at -O1 or higher) when a const
global is initialised with a non-POD initialiser.  invariant.end is
apparently not generated at all.

Do the stripping in ReplacePtrsWithInts for consistency with the
existing lifetime.start/end stripping.

BUG=https://code.google.com/p/nativeclient/issues/detail?id=3443
TEST=PNaCl toolchain trybots

Review URL: https://codereview.chromium.org/15995004

3 files changed, 21 insertions, 4 deletions

diff --git a/lib/Analysis/NaCl/PNaClABIVerifyModule.cpp b/lib/Analysis/NaCl/PNaClABIVerifyModule.cpp
index 9b2def5ac4..d977175b67 100644
--- a/lib/Analysis/NaCl/PNaClABIVerifyModule.cpp
+++ b/lib/Analysis/NaCl/PNaClABIVerifyModule.cpp
@@ -161,8 +161,6 @@ bool PNaClABIVerifyModule::isWhitelistedIntrinsic(const Function *F,
     default: return false;
     // (1) Always allowed.
     case Intrinsic::bswap: return isWhitelistedBswap(F);
-    case Intrinsic::invariant_end:
-    case Intrinsic::invariant_start:
     case Intrinsic::memcpy:
     case Intrinsic::memmove:
     case Intrinsic::memset:
@@ -215,6 +213,8 @@ bool PNaClABIVerifyModule::isWhitelistedIntrinsic(const Function *F,
     // See https://code.google.com/p/nativeclient/issues/detail?id=3443
     case Intrinsic::lifetime_end:
     case Intrinsic::lifetime_start:
+    case Intrinsic::invariant_end:
+    case Intrinsic::invariant_start:
       return false;
 
     // (3) Dev intrinsics.
diff --git a/lib/Transforms/NaCl/ReplacePtrsWithInts.cpp b/lib/Transforms/NaCl/ReplacePtrsWithInts.cpp
index 00d374dc7b..9be459d986 100644
--- a/lib/Transforms/NaCl/ReplacePtrsWithInts.cpp
+++ b/lib/Transforms/NaCl/ReplacePtrsWithInts.cpp
@@ -38,7 +38,8 @@
 //  * a bitcast of an InherentPtr.
 //
 // This pass currently strips out lifetime markers (that is, calls to
-// the llvm.lifetime.start/end intrinsics).
+// the llvm.lifetime.start/end intrinsics) and invariant markers
+// (calls to llvm.invariant.start/end).
 //
 //===----------------------------------------------------------------------===//
 
@@ -407,7 +408,9 @@ static void ConvertInstruction(DataLayout *DL, Type *IntPtrType,
   } else if (CallInst *Call = dyn_cast<CallInst>(Inst)) {
     if (IntrinsicInst *ICall = dyn_cast<IntrinsicInst>(Inst)) {
       if (ICall->getIntrinsicID() == Intrinsic::lifetime_start ||
-          ICall->getIntrinsicID() == Intrinsic::lifetime_end) {
+          ICall->getIntrinsicID() == Intrinsic::lifetime_end ||
+          ICall->getIntrinsicID() == Intrinsic::invariant_start ||
+          ICall->getIntrinsicID() == Intrinsic::invariant_end) {
         // Remove alloca lifetime markers for now.  This is because
         // the GVN pass can introduce lifetime markers taking PHI
         // nodes as arguments.  If ReplacePtrsWithInts converts the
@@ -416,6 +419,8 @@ static void ConvertInstruction(DataLayout *DL, Type *IntPtrType,
         // not safe in general.  So, until LLVM better defines the
         // semantics of lifetime markers, we drop them all.  See:
         // https://code.google.com/p/nativeclient/issues/detail?id=3443
+        // We do the same for invariant.start/end because they work in
+        // a similar way.
         Inst->eraseFromParent();
       } else {
         FC->convertInPlace(Inst);
diff --git a/test/Transforms/NaCl/replace-ptrs-with-ints.ll b/test/Transforms/NaCl/replace-ptrs-with-ints.ll
index bab6101848..d7e85f6da6 100644
--- a/test/Transforms/NaCl/replace-ptrs-with-ints.ll
+++ b/test/Transforms/NaCl/replace-ptrs-with-ints.ll
@@ -447,6 +447,8 @@ define void @debug_value(i32 %val, i8* %ptr) {
 
 
 declare void @llvm.lifetime.start(i64 %size, i8* %ptr)
+declare void @llvm.invariant.start(i64 %size, i8* %ptr)
+declare void @llvm.invariant.end(i64 %size, i8* %ptr)
 
 ; GVN can introduce the following horrible corner case of a lifetime
 ; marker referencing a PHI node.  But we convert the phi to i32 type,
@@ -486,6 +488,16 @@ define void @alloca_lifetime_via_bitcast() {
 ; CHECK-NEXT: %buf = alloca [4 x i8]
 ; CHECK-NEXT: ret void
 
+define void @strip_invariant_markers() {
+  %buf = alloca i8
+  call void @llvm.invariant.start(i64 1, i8* %buf)
+  call void @llvm.invariant.end(i64 1, i8* %buf)
+  ret void
+}
+; CHECK: define void @strip_invariant_markers() {
+; CHECK-NEXT: %buf = alloca [1 x i8]
+; CHECK-NEXT: ret void
+
 
 ; "nocapture" and "noalias" only apply to pointers, so must be stripped.
 define void @nocapture_attr(i8* nocapture noalias %ptr) {