3 files changed, 17 insertions, 11 deletions
diff --git a/contrib/llvm/lib/Analysis/BasicAliasAnalysis.cpp b/contrib/llvm/lib/Analysis/BasicAliasAnalysis.cpp
index 1a24ae3dba15..f9ecbc043261 100644
--- a/contrib/llvm/lib/Analysis/BasicAliasAnalysis.cpp
+++ b/contrib/llvm/lib/Analysis/BasicAliasAnalysis.cpp
@@ -801,14 +801,15 @@ ModRefInfo BasicAAResult::getModRefInfo(ImmutableCallSite CS,
 
   const Value *Object = GetUnderlyingObject(Loc.Ptr, DL);
 
-  // If this is a tail call and Loc.Ptr points to a stack location, we know that
-  // the tail call cannot access or modify the local stack.
-  // We cannot exclude byval arguments here; these belong to the caller of
-  // the current function not to the current function, and a tail callee
-  // may reference them.
+  // Calls marked 'tail' cannot read or write allocas from the current frame
+  // because the current frame might be destroyed by the time they run. However,
+  // a tail call may use an alloca with byval. Calling with byval copies the
+  // contents of the alloca into argument registers or stack slots, so there is
+  // no lifetime issue.
   if (isa<AllocaInst>(Object))
     if (const CallInst *CI = dyn_cast<CallInst>(CS.getInstruction()))
-      if (CI->isTailCall())
+      if (CI->isTailCall() &&
+          !CI->getAttributes().hasAttrSomewhere(Attribute::ByVal))
         return ModRefInfo::NoModRef;
 
   // If the pointer is to a locally allocated object that does not escape,
diff --git a/contrib/llvm/lib/Analysis/InstructionSimplify.cpp b/contrib/llvm/lib/Analysis/InstructionSimplify.cpp
index f991291f565a..5e72798d459a 100644
--- a/contrib/llvm/lib/Analysis/InstructionSimplify.cpp
+++ b/contrib/llvm/lib/Analysis/InstructionSimplify.cpp
@@ -1338,7 +1338,7 @@ static Value *SimplifyLShrInst(Value *Op0, Value *Op1, bool isExact,
     const KnownBits YKnown = computeKnownBits(Y, Q.DL, 0, Q.AC, Q.CxtI, Q.DT);
     const unsigned Width = Op0->getType()->getScalarSizeInBits();
     const unsigned EffWidthY = Width - YKnown.countMinLeadingZeros();
-    if (EffWidthY <= ShRAmt->getZExtValue())
+    if (ShRAmt->uge(EffWidthY))
       return X;
   }
 
@@ -1878,9 +1878,9 @@ static Value *SimplifyAndInst(Value *Op0, Value *Op1, const SimplifyQuery &Q,
       match(Op0, m_c_Or(m_CombineAnd(m_NUWShl(m_Value(X), m_APInt(ShAmt)),
                                      m_Value(XShifted)),
                         m_Value(Y)))) {
-    const unsigned ShftCnt = ShAmt->getZExtValue();
-    const KnownBits YKnown = computeKnownBits(Y, Q.DL, 0, Q.AC, Q.CxtI, Q.DT);
     const unsigned Width = Op0->getType()->getScalarSizeInBits();
+    const unsigned ShftCnt = ShAmt->getLimitedValue(Width);
+    const KnownBits YKnown = computeKnownBits(Y, Q.DL, 0, Q.AC, Q.CxtI, Q.DT);
     const unsigned EffWidthY = Width - YKnown.countMinLeadingZeros();
     if (EffWidthY <= ShftCnt) {
       const KnownBits XKnown = computeKnownBits(X, Q.DL, 0, Q.AC, Q.CxtI,
diff --git a/contrib/llvm/lib/Analysis/MemorySSA.cpp b/contrib/llvm/lib/Analysis/MemorySSA.cpp
index f57d490ce96e..b38c0c4f1439 100644
--- a/contrib/llvm/lib/Analysis/MemorySSA.cpp
+++ b/contrib/llvm/lib/Analysis/MemorySSA.cpp
@@ -258,13 +258,18 @@ static ClobberAlias instructionClobbersQuery(MemoryDef *MD,
 
   if (const IntrinsicInst *II = dyn_cast<IntrinsicInst>(DefInst)) {
     // These intrinsics will show up as affecting memory, but they are just
-    // markers.
+    // markers, mostly.
+    //
+    // FIXME: We probably don't actually want MemorySSA to model these at all
+    // (including creating MemoryAccesses for them): we just end up inventing
+    // clobbers where they don't really exist at all. Please see D43269 for
+    // context.
     switch (II->getIntrinsicID()) {
     case Intrinsic::lifetime_start:
       if (UseCS)
         return {false, NoAlias};
       AR = AA.alias(MemoryLocation(II->getArgOperand(1)), UseLoc);
-      return {AR == MustAlias, AR};
+      return {AR != NoAlias, AR};
     case Intrinsic::lifetime_end:
     case Intrinsic::invariant_start:
     case Intrinsic::invariant_end: