[PATCH] DataFlowSanitizer: Make unreachable BBs verify under the args ABI.

[Peter Collingbourne]

Hi eugenis,

http://llvm-reviews.chandlerc.com/D1316

Files:
  lib/Transforms/Instrumentation/DataFlowSanitizer.cpp
  test/Instrumentation/DataFlowSanitizer/args-unreachable-bb.ll

Index: lib/Transforms/Instrumentation/DataFlowSanitizer.cpp
===================================================================
--- lib/Transforms/Instrumentation/DataFlowSanitizer.cpp
+++ lib/Transforms/Instrumentation/DataFlowSanitizer.cpp
@@ -410,6 +410,23 @@
     std::copy(df_begin(&(*i)->getEntryBlock()), df_end(&(*i)->getEntryBlock()),
               std::back_inserter(BBList));
 
+    // Unused basic blocks will not be instrumented.  This is okay, because
+    // they are unreachable.  But we need to modify any return instructions in
+    // these BBs to return a value of the correct type in order to pass the
+    // verifier.  This is easier than just deleting them because they may be
+    // referenced by phi nodes (and each other).
+    Type *RetTy = (*i)->getReturnType();
+    if (!RetTy->isVoidTy()) {
+      SmallPtrSet<BasicBlock *, 4> BBSet;
+      BBSet.insert(BBList.begin(), BBList.end());
+      for (Function::iterator bi = (*i)->begin(), be = (*i)->end(); bi != be;
+           ++bi) {
+        if (!BBSet.count(&*bi))
+          if (ReturnInst *RI = dyn_cast<ReturnInst>(bi->getTerminator()))
+            RI->setOperand(0, UndefValue::get(RetTy));
+      }
+    }
+
     for (llvm::SmallVector<BasicBlock *, 4>::iterator i = BBList.begin(),
                                                       e = BBList.end();
          i != e; ++i) {
Index: test/Instrumentation/DataFlowSanitizer/args-unreachable-bb.ll
===================================================================
--- /dev/null
+++ test/Instrumentation/DataFlowSanitizer/args-unreachable-bb.ll
@@ -0,0 +1,13 @@
+; RUN: opt < %s -dfsan -verify -dfsan-args-abi -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"
+
+define i8 @unreachable_bb() {
+  ; CHECK: @unreachable_bb
+  ; CHECK: ret { i8, i16 } { i8 1, i16 0 }
+  ; CHECK: bb2:
+  ; CHECK: ret { i8, i16 } undef
+  ret i8 1
+
+bb2:
+  ret i8 2
+}
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