Implement strip.invariant.group

Summary:
This patch introduce new intrinsic -
strip.invariant.group that was described in the
RFC: Devirtualization v2

Reviewers: rsmith, hfinkel, nlopes, sanjoy, amharc, kuhar

Subscribers: arsenm, nhaehnle, JDevlieghere, hiraditya, xbolva00, llvm-commits

Differential Revision: https://reviews.llvm.org/D47103

Co-authored-by: Krzysztof Pszeniczny <krzysztof.pszeniczny@gmail.com>
llvm-svn: 336073

1 files changed, 12 insertions, 9 deletions

diff --git a/llvm/lib/Analysis/ValueTracking.cpp b/llvm/lib/Analysis/ValueTracking.cpp
index 12002de..16a3c7c 100644
--- a/llvm/lib/Analysis/ValueTracking.cpp
+++ b/llvm/lib/Analysis/ValueTracking.cpp
@@ -3404,8 +3404,9 @@ const Value *llvm::getArgumentAliasingToReturnedPointer(ImmutableCallSite CS) {
 }
 
 bool llvm::isIntrinsicReturningPointerAliasingArgumentWithoutCapturing(
-      ImmutableCallSite CS) {
-  return CS.getIntrinsicID() == Intrinsic::launder_invariant_group;
+    ImmutableCallSite CS) {
+  return CS.getIntrinsicID() == Intrinsic::launder_invariant_group ||
+         CS.getIntrinsicID() == Intrinsic::strip_invariant_group;
 }
 
 /// \p PN defines a loop-variant pointer to an object.  Check if the
@@ -3454,13 +3455,15 @@ Value *llvm::GetUnderlyingObject(Value *V, const DataLayout &DL,
       return V;
     } else {
       if (auto CS = CallSite(V)) {
-        // Note: getArgumentAliasingToReturnedPointer keeps it in sync with
-        // CaptureTracking, which is needed for correctness.  This is because
-        // some intrinsics like launder.invariant.group returns pointers that
-        // are aliasing it's argument, which is known to CaptureTracking.
-        // If AliasAnalysis does not use the same information, it could assume
-        // that pointer returned from launder does not alias it's argument
-        // because launder could not return it if the pointer was not captured.
+        // CaptureTracking can know about special capturing properties of some
+        // intrinsics like launder.invariant.group, that can't be expressed with
+        // the attributes, but have properties like returning aliasing pointer.
+        // Because some analysis may assume that nocaptured pointer is not
+        // returned from some special intrinsic (because function would have to
+        // be marked with returns attribute), it is crucial to use this function
+        // because it should be in sync with CaptureTracking. Not using it may
+        // cause weird miscompilations where 2 aliasing pointers are assumed to
+        // noalias.
         if (auto *RP = getArgumentAliasingToReturnedPointer(CS)) {
           V = RP;
           continue;