From b54a8d62a4859bf69e9b6e877a6e73fdc67ced40 Mon Sep 17 00:00:00 2001
From: George Burgess IV <george.burgess.iv@gmail.com>
Date: Tue, 10 Mar 2015 02:40:06 +0000
Subject: [PATCH] Added special handling for inttoptr in CFLAA.

We now treat pointers given to ptrtoint and pointers retrieved from
inttoptr as similar to arguments or globals (can alias anything, etc.)

This solves some of the problems we were having with giving incorrect
results.

llvm-svn: 231741
---
 llvm/lib/Analysis/CFLAliasAnalysis.cpp        | 32 +++++---
 .../Analysis/CFLAliasAnalysis/branch-alias.ll | 73 +++++++++++++++++++
 2 files changed, 95 insertions(+), 10 deletions(-)
 create mode 100644 llvm/test/Analysis/CFLAliasAnalysis/branch-alias.ll

diff --git a/llvm/lib/Analysis/CFLAliasAnalysis.cpp b/llvm/lib/Analysis/CFLAliasAnalysis.cpp
index c2c054f3f2ec..da5e95ff48d5 100644
--- a/llvm/lib/Analysis/CFLAliasAnalysis.cpp
+++ b/llvm/lib/Analysis/CFLAliasAnalysis.cpp
@@ -85,11 +85,13 @@ typedef unsigned StratifiedAttr;
 LLVM_CONSTEXPR unsigned MaxStratifiedAttrIndex = NumStratifiedAttrs;
 LLVM_CONSTEXPR unsigned AttrAllIndex = 0;
 LLVM_CONSTEXPR unsigned AttrGlobalIndex = 1;
-LLVM_CONSTEXPR unsigned AttrFirstArgIndex = 2;
+LLVM_CONSTEXPR unsigned AttrUnknownIndex = 2;
+LLVM_CONSTEXPR unsigned AttrFirstArgIndex = 3;
 LLVM_CONSTEXPR unsigned AttrLastArgIndex = MaxStratifiedAttrIndex;
 LLVM_CONSTEXPR unsigned AttrMaxNumArgs = AttrLastArgIndex - AttrFirstArgIndex;
 
 LLVM_CONSTEXPR StratifiedAttr AttrNone = 0;
+LLVM_CONSTEXPR StratifiedAttr AttrUnknown = 1 << AttrUnknownIndex;
 LLVM_CONSTEXPR StratifiedAttr AttrAll = ~AttrNone;
 
 // \brief StratifiedSets call for knowledge of "direction", so this is how we
@@ -263,6 +265,16 @@ public:
     llvm_unreachable("Unsupported instruction encountered");
   }
 
+  void visitPtrToIntInst(PtrToIntInst &Inst) {
+    auto *Ptr = Inst.getOperand(0);
+    Output.push_back(Edge(Ptr, Ptr, EdgeType::Assign, AttrUnknown));
+  }
+
+  void visitIntToPtrInst(IntToPtrInst &Inst) {
+    auto *Ptr = &Inst;
+    Output.push_back(Edge(Ptr, Ptr, EdgeType::Assign, AttrUnknown));
+  }
+
   void visitCastInst(CastInst &Inst) {
     Output.push_back(Edge(&Inst, Inst.getOperand(0), EdgeType::Assign,
                           AttrNone));
@@ -931,16 +943,16 @@ static FunctionInfo buildSetsFrom(CFLAliasAnalysis &Analysis, Function *Fn) {
           break;
         }
 
-        if (Added) {
-          auto Aliasing = Weight.second;
-          if (auto MaybeCurIndex = valueToAttrIndex(CurValue))
-            Aliasing.set(*MaybeCurIndex);
-          if (auto MaybeOtherIndex = valueToAttrIndex(OtherValue))
-            Aliasing.set(*MaybeOtherIndex);
-          Builder.noteAttributes(CurValue, Aliasing);
-          Builder.noteAttributes(OtherValue, Aliasing);
+        auto Aliasing = Weight.second;
+        if (auto MaybeCurIndex = valueToAttrIndex(CurValue))
+          Aliasing.set(*MaybeCurIndex);
+        if (auto MaybeOtherIndex = valueToAttrIndex(OtherValue))
+          Aliasing.set(*MaybeOtherIndex);
+        Builder.noteAttributes(CurValue, Aliasing);
+        Builder.noteAttributes(OtherValue, Aliasing);
+
+        if (Added)
           Worklist.push_back(OtherNode);
-        }
       }
     }
   }
diff --git a/llvm/test/Analysis/CFLAliasAnalysis/branch-alias.ll b/llvm/test/Analysis/CFLAliasAnalysis/branch-alias.ll
new file mode 100644
index 000000000000..8307462928e7
--- /dev/null
+++ b/llvm/test/Analysis/CFLAliasAnalysis/branch-alias.ll
@@ -0,0 +1,73 @@
+; Makes sure that we give up on some pathological cases with inttoptr/ptrtoint
+;
+; @ptr_test was generated from the following C code:
+;  void ptr_test() {
+;    int* A;
+;    unsigned long RefCopy = 0;
+;    for (int i = 0; i < 8*sizeof(&A); ++i) {
+;      if ((unsigned long)&A & (1UL << i))
+;        RefCopy |= 1UL << i;
+;    }
+;
+;    int** AliasA1 = (int**)RefCopy;
+;    int* ShouldAliasA = *AliasA1;
+;  }
+
+; RUN: opt < %s -cfl-aa -aa-eval -print-may-aliases -disable-output 2>&1 | FileCheck %s
+
+; CHECK: Function: ptr_test
+define void @ptr_test() #0 {
+  ; CHECK: MayAlias: i32** %A, i32** %ShouldAliasA
+  ; CHECK-NOT: %AliasA1
+entry:
+  %A = alloca i32*, align 8
+  %RefCopy = alloca i64, align 8
+  %i = alloca i32, align 4
+  %AliasA1 = alloca i32**, align 8
+  %ShouldAliasA = alloca i32*, align 8
+  store i64 0, i64* %RefCopy, align 8
+  store i32 0, i32* %i, align 4
+  br label %for.cond
+
+for.cond:                                         ; preds = %for.inc, %entry
+  %0 = load i32, i32* %i, align 4
+  %conv = sext i32 %0 to i64
+  %cmp = icmp ult i64 %conv, 64
+  br i1 %cmp, label %for.body, label %for.end
+
+for.body:                                         ; preds = %for.cond
+  %1 = ptrtoint i32** %A to i64
+  %2 = load i32, i32* %i, align 4
+  %sh_prom = zext i32 %2 to i64
+  %shl = shl i64 1, %sh_prom
+  %and = and i64 %1, %shl
+  %tobool = icmp ne i64 %and, 0
+  br i1 %tobool, label %if.then, label %if.end
+
+if.then:                                          ; preds = %for.body
+  %3 = load i32, i32* %i, align 4
+  %sh_prom2 = zext i32 %3 to i64
+  %shl3 = shl i64 1, %sh_prom2
+  %4 = load i64, i64* %RefCopy, align 8
+  %or = or i64 %4, %shl3
+  store i64 %or, i64* %RefCopy, align 8
+  br label %if.end
+
+if.end:                                           ; preds = %if.then, %for.body
+  br label %for.inc
+
+for.inc:                                          ; preds = %if.end
+  %5 = load i32, i32* %i, align 4
+  %inc = add nsw i32 %5, 1
+  store i32 %inc, i32* %i, align 4
+  br label %for.cond
+
+for.end:                                          ; preds = %for.cond
+  %6 = load i64, i64* %RefCopy, align 8
+  %7 = inttoptr i64 %6 to i32**
+  store i32** %7, i32*** %AliasA1, align 8
+  %8 = load i32**, i32*** %AliasA1, align 8
+  %9 = load i32*, i32** %8, align 8
+  store i32* %9, i32** %ShouldAliasA, align 8
+  ret void
+}