Index: lib/Analysis/CaptureTracking.cpp
===================================================================
--- lib/Analysis/CaptureTracking.cpp
+++ lib/Analysis/CaptureTracking.cpp
@@ -27,6 +27,7 @@
 #include "llvm/IR/Dominators.h"
 #include "llvm/IR/Instructions.h"
 #include "llvm/IR/IntrinsicInst.h"
+#include "llvm/IR/Intrinsics.h"
 
 using namespace llvm;
 
@@ -233,9 +234,35 @@
     Instruction *I = cast<Instruction>(U->getUser());
     V = U->get();
 
+    auto Passthrough = [&]() {
+      // The original value is not captured via this if the new value isn't.
+      Count = 0;
+      for (Use &UU : I->uses()) {
+        // If there are lots of uses, conservatively say that the value
+        // is captured to avoid taking too much compile time.
+        if (Count++ >= Threshold) {
+          Tracker->tooManyUses();
+          return false;
+        }
+
+        if (Visited.insert(&UU).second)
+          if (Tracker->shouldExplore(&UU))
+            Worklist.push_back(&UU);
+      }
+
+      return true;
+    };
+
     switch (I->getOpcode()) {
     case Instruction::Call:
     case Instruction::Invoke: {
+      if (auto *II = dyn_cast<IntrinsicInst>(I))
+        if (II->getIntrinsicID() == Intrinsic::noalias) {
+          if (!Passthrough())
+            return;
+          break;
+        }
+
       CallSite CS(I);
       // Not captured if the callee is readonly, doesn't return a copy through
       // its return value and doesn't unwind (a readonly function can leak bits
@@ -312,18 +339,8 @@
     case Instruction::PHI:
     case Instruction::Select:
     case Instruction::AddrSpaceCast:
-      // The original value is not captured via this if the new value isn't.
-      Count = 0;
-      for (Use &UU : I->uses()) {
-        // If there are lots of uses, conservatively say that the value
-        // is captured to avoid taking too much compile time.
-        if (Count++ >= Threshold)
-          return Tracker->tooManyUses();
-
-        if (Visited.insert(&UU).second)
-          if (Tracker->shouldExplore(&UU))
-            Worklist.push_back(&UU);
-      }
+      if (!Passthrough())
+        return;
       break;
     case Instruction::ICmp: {
       // Don't count comparisons of a no-alias return value against null as
Index: test/Transforms/FunctionAttrs/nocapture.ll
===================================================================
--- test/Transforms/FunctionAttrs/nocapture.ll
+++ test/Transforms/FunctionAttrs/nocapture.ll
@@ -91,6 +91,22 @@
 	ret i32 %val
 }
 
+; CHECK: define i32 @nc1a(i32* %q, i32* nocapture %p, i1 %b)
+define i32 @nc1a(i32* %q, i32* %p, i1 %b) {
+e:
+        %pa = call i32* @llvm.noalias.p0i32(i32* %p, metadata !1)
+	br label %l
+l:
+	%x = phi i32* [ %pa, %e ]
+	%y = phi i32* [ %q, %e ]
+	%tmp = bitcast i32* %x to i32*		; <i32*> [#uses=2]
+	%tmp2 = select i1 %b, i32* %tmp, i32* %y
+	%val = load i32, i32* %tmp2		; <i32> [#uses=1]
+	store i32 0, i32* %tmp
+	store i32* %y, i32** @g
+	ret i32 %val
+}
+
 ; CHECK: define i32 @nc1_addrspace(i32* %q, i32 addrspace(1)* nocapture %p, i1 %b)
 define i32 @nc1_addrspace(i32* %q, i32 addrspace(1)* %p, i1 %b) {
 e:
@@ -218,3 +234,9 @@
   store volatile i32 0, i32* %gep, align 4
   ret void
 }
+
+declare i32* @llvm.noalias.p0i32(i32*, metadata) nounwind
+
+!0 = !{!0, !"some domain"}
+!1 = !{!1, !0, !"some scope"}
+