[dfsan] Add a test case for phi

[morehouse]

LGTM

[stephan.yichao.zhao]

https://github.com/llvm/llvm-project/commit/baa005c96ce610e9ee91ef55a3a1b1eacd5a0a27

llvm/test/Instrumentation/DataFlowSanitizer/phi.ll

+; RUN: opt < %s -dfsan -S | FileCheck %s
+target datalayout = "e-p:64:64:64-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:64:64-f32:32:32-f64:64:64-v64:64:64-v128:128:128-a0:0:64-s0:64:64-f80:128:128-n8:16:32:64-S128"
+target triple = "x86_64-unknown-linux-gnu"
+
+define {i32, i32} @test({i32, i32} %a, i1 %c) {
+  ; CHECK: [[E0:%.*]] = load i16, i16* getelementptr inbounds ([64 x i16], [64 x i16]* @__dfsan_arg_tls, i64 0, i64 0), align 2
+  ; CHECK: [[E3:%.*]] = phi i16 [ [[E0]], %T ], [ [[E0]], %F ]
+  ; CHECK: store i16 [[E3]], i16* @__dfsan_retval_tls, align 2
+
+entry:
+  br i1 %c, label %T, label %F
+  
+T:
+  %at = insertvalue {i32, i32} %a, i32 1, 0
+  br label %done
+  
+F:
+  %af = insertvalue {i32, i32} %a, i32 1, 1
+  br label %done
+  
+done:
+  %b = phi {i32, i32} [%at, %T], [%af, %F]
+  ret {i32, i32} %b  
+}