[CFL-AA] CFL-AA should not assert on an va_arg instruction

The CFL-AA implementation was missing a visit* routine for va_arg instructions,
causing it to assert when run on a function that had one. For now, handle these
in a conservative way.

Fixes PR20954.

llvm-svn: 219718

llvm/lib/Analysis/CFLAliasAnalysis.cpp

@@ -317,6 +317,17 @@ public:
     Output.push_back(Edge(Ptr, Val, EdgeType::Dereference, AttrNone));
   }
 
+  void visitVAArgInst(VAArgInst &Inst) {
+    // We can't fully model va_arg here. For *Ptr = Inst.getOperand(0), it does
+    // two things:
+    //  1. Loads a value from *((T*)*Ptr).
+    //  2. Increments (stores to) *Ptr by some target-specific amount.
+    // For now, we'll handle this like a landingpad instruction (by placing the
+    // result in its own group, and having that group alias externals).
+    auto *Val = &Inst;
+    Output.push_back(Edge(Val, Val, EdgeType::Assign, AttrAll));
+  }
+
   static bool isFunctionExternal(Function *Fn) {
     return Fn->isDeclaration() || !Fn->hasLocalLinkage();
   }

llvm/test/Analysis/CFLAliasAnalysis/va.ll

@@ -0,0 +1,29 @@
+; RUN: opt < %s -cfl-aa -aa-eval -print-may-aliases -disable-output 2>&1 | FileCheck %s
+
+; CHECK-LABEL: Function: test1
+; CHECK: 0 no alias responses
+
+define i32 @test1(i32 %X, ...) {
+  ; Initialize variable argument processing
+  %ap = alloca i8*
+  %ap2 = bitcast i8** %ap to i8*
+  call void @llvm.va_start(i8* %ap2)
+
+  ; Read a single integer argument
+  %tmp = va_arg i8** %ap, i32
+
+  ; Demonstrate usage of llvm.va_copy and llvm.va_end
+  %aq = alloca i8*
+  %aq2 = bitcast i8** %aq to i8*
+  call void @llvm.va_copy(i8* %aq2, i8* %ap2)
+  call void @llvm.va_end(i8* %aq2)
+
+  ; Stop processing of arguments.
+  call void @llvm.va_end(i8* %ap2)
+  ret i32 %tmp
+}
+
+declare void @llvm.va_start(i8*)
+declare void @llvm.va_copy(i8*, i8*)
+declare void @llvm.va_end(i8*)
+