From 37abc488a0527bb682af5aa6c4f376b5b99d67e4 Mon Sep 17 00:00:00 2001
From: Nick Lewycky <nicholas@mxc.ca>
Date: Mon, 23 Jan 2012 00:05:17 +0000
Subject: [PATCH] Make Value::isDereferenceablePointer() handle unreachable
 code blocks. (This returns false in the event the computation feeding into
 the pointer is unreachable, which maybe ought to be true -- but this is at
 least consistent with undef->isDereferenceablePointer().) Fixes PR11825!

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@148671 91177308-0d34-0410-b5e6-96231b3b80d8
---
 lib/VMCore/Value.cpp                          | 24 +++++++++++-----
 .../SimplifyCFG/unreachable-blocks.ll         | 28 +++++++++++++++++++
 2 files changed, 45 insertions(+), 7 deletions(-)
 create mode 100644 test/Transforms/SimplifyCFG/unreachable-blocks.ll

diff --git a/lib/VMCore/Value.cpp b/lib/VMCore/Value.cpp
index a5f1918e55d..207c06d2231 100644
--- a/lib/VMCore/Value.cpp
+++ b/lib/VMCore/Value.cpp
@@ -349,7 +349,8 @@ Value *Value::stripPointerCasts() {
 
 /// isDereferenceablePointer - Test if this value is always a pointer to
 /// allocated and suitably aligned memory for a simple load or store.
-bool Value::isDereferenceablePointer() const {
+static bool isDereferenceablePointer(const Value *V,
+                                     SmallPtrSet<const Value *, 32> &Visited) {
   // Note that it is not safe to speculate into a malloc'd region because
   // malloc may return null.
   // It's also not always safe to follow a bitcast, for example:
@@ -358,20 +359,22 @@ bool Value::isDereferenceablePointer() const {
   // be handled using TargetData to check sizes and alignments though.
 
   // These are obviously ok.
-  if (isa<AllocaInst>(this)) return true;
+  if (isa<AllocaInst>(V)) return true;
 
   // Global variables which can't collapse to null are ok.
-  if (const GlobalVariable *GV = dyn_cast<GlobalVariable>(this))
+  if (const GlobalVariable *GV = dyn_cast<GlobalVariable>(V))
     return !GV->hasExternalWeakLinkage();
 
   // byval arguments are ok.
-  if (const Argument *A = dyn_cast<Argument>(this))
+  if (const Argument *A = dyn_cast<Argument>(V))
     return A->hasByValAttr();
-  
+
   // For GEPs, determine if the indexing lands within the allocated object.
-  if (const GEPOperator *GEP = dyn_cast<GEPOperator>(this)) {
+  if (const GEPOperator *GEP = dyn_cast<GEPOperator>(V)) {
     // Conservatively require that the base pointer be fully dereferenceable.
-    if (!GEP->getOperand(0)->isDereferenceablePointer())
+    if (!Visited.insert(GEP->getOperand(0)))
+      return false;
+    if (!isDereferenceablePointer(GEP->getOperand(0), Visited))
       return false;
     // Check the indices.
     gep_type_iterator GTI = gep_type_begin(GEP);
@@ -405,6 +408,13 @@ bool Value::isDereferenceablePointer() const {
   return false;
 }
 
+/// isDereferenceablePointer - Test if this value is always a pointer to
+/// allocated and suitably aligned memory for a simple load or store.
+bool Value::isDereferenceablePointer() const {
+  SmallPtrSet<const Value *, 32> Visited;
+  return ::isDereferenceablePointer(this, Visited);
+}
+
 /// DoPHITranslation - If this value is a PHI node with CurBB as its parent,
 /// return the value in the PHI node corresponding to PredBB.  If not, return
 /// ourself.  This is useful if you want to know the value something has in a
diff --git a/test/Transforms/SimplifyCFG/unreachable-blocks.ll b/test/Transforms/SimplifyCFG/unreachable-blocks.ll
new file mode 100644
index 00000000000..1df0eab6259
--- /dev/null
+++ b/test/Transforms/SimplifyCFG/unreachable-blocks.ll
@@ -0,0 +1,28 @@
+; RUN: opt -simplifycfg < %s -disable-output
+
+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"
+target triple = "x86_64-pc-linux-gnu"
+
+; PR11825
+define void @test1() {
+entry:
+  br label %return
+
+while_block:                                      ; preds = %and_if_cont2, %and_if_cont
+  %newlen = sub i32 %newlen, 1
+  %newptr = getelementptr i8* %newptr, i64 1
+  %test = icmp sgt i32 %newlen, 0
+  br i1 %test, label %and_if1, label %and_if_cont2
+
+and_if1:                                          ; preds = %while_block
+  %char = load i8* %newptr
+  %test2 = icmp ule i8 %char, 32
+  br label %and_if_cont2
+
+and_if_cont2:                                     ; preds = %and_if1, %while_block
+  %a18 = phi i1 [ %test, %while_block ], [ %test2, %and_if1 ]
+  br i1 %a18, label %while_block, label %return
+
+return:                                           ; preds = %and_if_cont2, %and_if_cont
+  ret void
+}