[Attributor][FIX] Don't crash on ptr2int/int2ptr instructions

An integer isn't allowed in getAlignmentForValue so we need to stop at a
ptr2int instruction during exploration.

llvm/lib/Transforms/IPO/Attributor.cpp

@@ -3466,7 +3466,8 @@ static unsigned int getKnownAlignForUse(Attributor &A,
   // We need to follow common pointer manipulation uses to the accesses they
   // feed into.
   if (isa<CastInst>(I)) {
-    TrackUse = true;
+    // Follow all but ptr2int casts.
+    TrackUse = !isa<PtrToIntInst>(I);
     return 0;
   }
   if (auto *GEP = dyn_cast<GetElementPtrInst>(I)) {

llvm/test/Transforms/Attributor/align.ll

@@ -398,5 +398,15 @@ define void @test12-6(i32* align 4 %p) {
   ret void
 }
 
+; Don't crash on ptr2int/int2ptr uses.
+define i64 @ptr2int(i32* %p) {
+  %p2i = ptrtoint i32* %p to i64
+  ret i64 %p2i
+}
+define i64* @int2ptr(i64 %i) {
+  %i2p = inttoptr i64 %i to i64*
+  ret i64* %i2p
+}
+
 attributes #0 = { nounwind uwtable noinline }
 attributes #1 = { uwtable noinline }