[llvm] r231743 - Added ConstantExpr support to CFLAA.
George Burgess IV
george.burgess.iv at gmail.com
Mon Mar 9 19:58:15 PDT 2015
Author: gbiv
Date: Mon Mar 9 21:58:15 2015
New Revision: 231743
URL: http://llvm.org/viewvc/llvm-project?rev=231743&view=rev
Log:
Added ConstantExpr support to CFLAA.
CFLAA didn't know how to properly handle ConstantExprs; it would silently
ignore them. This was a problem if the ConstantExpr is, say, a GEP of a global,
because CFLAA wouldn't realize that there's a global there. :)
Modified:
llvm/trunk/lib/Analysis/CFLAliasAnalysis.cpp
llvm/trunk/test/Analysis/CFLAliasAnalysis/asm-global-bugfix.ll
llvm/trunk/test/Analysis/CFLAliasAnalysis/const-expr-gep.ll
llvm/trunk/test/Analysis/CFLAliasAnalysis/stratified-attrs-indexing.ll
Modified: llvm/trunk/lib/Analysis/CFLAliasAnalysis.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Analysis/CFLAliasAnalysis.cpp?rev=231743&r1=231742&r2=231743&view=diff
==============================================================================
--- llvm/trunk/lib/Analysis/CFLAliasAnalysis.cpp (original)
+++ llvm/trunk/lib/Analysis/CFLAliasAnalysis.cpp Mon Mar 9 21:58:15 2015
@@ -47,6 +47,7 @@
#include "llvm/Support/ErrorHandling.h"
#include <algorithm>
#include <cassert>
+#include <memory>
#include <forward_list>
#include <tuple>
@@ -231,6 +232,10 @@ public:
// Comparisons between global variables and other constants should be
// handled by BasicAA.
+ // TODO: ConstantExpr handling -- CFLAA may report NoAlias when comparing
+ // a GlobalValue and ConstantExpr, but every query needs to have at least
+ // one Value tied to a Function, and neither GlobalValues nor ConstantExprs
+ // are.
if (isa<Constant>(LocA.Ptr) && isa<Constant>(LocB.Ptr)) {
return AliasAnalysis::alias(LocA, LocB);
}
@@ -389,7 +394,7 @@ public:
// I put this here to give us an upper bound on time taken by IPA. Is it
// really (realistically) needed? Keep in mind that we do have an n^2 algo.
- if (std::distance(Args.begin(), Args.end()) > (int) MaxSupportedArgs)
+ if (std::distance(Args.begin(), Args.end()) > (int)MaxSupportedArgs)
return false;
// Exit early if we'll fail anyway
@@ -747,6 +752,25 @@ static Level directionOfEdgeType(EdgeTyp
static void buildGraphFrom(CFLAliasAnalysis &, Function *,
SmallVectorImpl<Value *> &, NodeMapT &, GraphT &);
+// Gets the edges of a ConstantExpr as if it was an Instruction. This
+// function also acts on any nested ConstantExprs, adding the edges
+// of those to the given SmallVector as well.
+static void constexprToEdges(CFLAliasAnalysis &, ConstantExpr &,
+ SmallVectorImpl<Edge> &);
+
+// Given an Instruction, this will add it to the graph, along with any
+// Instructions that are potentially only available from said Instruction
+// For example, given the following line:
+// %0 = load i16* getelementptr ([1 x i16]* @a, 0, 0), align 2
+// addInstructionToGraph would add both the `load` and `getelementptr`
+// instructions to the graph appropriately.
+static void addInstructionToGraph(CFLAliasAnalysis &, Instruction &,
+ SmallVectorImpl<Value *> &, NodeMapT &,
+ GraphT &);
+
+// Notes whether it would be pointless to add the given Value to our sets.
+static bool canSkipAddingToSets(Value *Val);
+
// Builds the graph + StratifiedSets for a function.
static FunctionInfo buildSetsFrom(CFLAliasAnalysis &, Function *);
@@ -818,6 +842,8 @@ static EdgeType flipWeight(EdgeType Init
static void argsToEdges(CFLAliasAnalysis &Analysis, Instruction *Inst,
SmallVectorImpl<Edge> &Output) {
+ assert(hasUsefulEdges(Inst) &&
+ "Expected instructions to have 'useful' edges");
GetEdgesVisitor v(Analysis, Output);
v.visit(Inst);
}
@@ -834,13 +860,41 @@ static Level directionOfEdgeType(EdgeTyp
llvm_unreachable("Incomplete switch coverage");
}
-// Aside: We may remove graph construction entirely, because it doesn't really
-// buy us much that we don't already have. I'd like to add interprocedural
-// analysis prior to this however, in case that somehow requires the graph
-// produced by this for efficient execution
-static void buildGraphFrom(CFLAliasAnalysis &Analysis, Function *Fn,
- SmallVectorImpl<Value *> &ReturnedValues,
- NodeMapT &Map, GraphT &Graph) {
+static void constexprToEdges(CFLAliasAnalysis &Analysis,
+ ConstantExpr &CExprToCollapse,
+ SmallVectorImpl<Edge> &Results) {
+ SmallVector<ConstantExpr *, 4> Worklist;
+ Worklist.push_back(&CExprToCollapse);
+
+ SmallVector<Edge, 8> ConstexprEdges;
+ while (!Worklist.empty()) {
+ auto *CExpr = Worklist.pop_back_val();
+ std::unique_ptr<Instruction> Inst(CExpr->getAsInstruction());
+
+ if (!hasUsefulEdges(Inst.get()))
+ continue;
+
+ ConstexprEdges.clear();
+ argsToEdges(Analysis, Inst.get(), ConstexprEdges);
+ for (auto &Edge : ConstexprEdges) {
+ if (Edge.From == Inst.get())
+ Edge.From = CExpr;
+ else if (auto *Nested = dyn_cast<ConstantExpr>(Edge.From))
+ Worklist.push_back(Nested);
+
+ if (Edge.To == Inst.get())
+ Edge.To = CExpr;
+ else if (auto *Nested = dyn_cast<ConstantExpr>(Edge.To))
+ Worklist.push_back(Nested);
+ }
+
+ Results.append(ConstexprEdges.begin(), ConstexprEdges.end());
+ }
+}
+
+static void addInstructionToGraph(CFLAliasAnalysis &Analysis, Instruction &Inst,
+ SmallVectorImpl<Value *> &ReturnedValues,
+ NodeMapT &Map, GraphT &Graph) {
const auto findOrInsertNode = [&Map, &Graph](Value *Val) {
auto Pair = Map.insert(std::make_pair(Val, GraphT::Node()));
auto &Iter = Pair.first;
@@ -851,40 +905,84 @@ static void buildGraphFrom(CFLAliasAnaly
return Iter->second;
};
+ // We don't want the edges of most "return" instructions, but we *do* want
+ // to know what can be returned.
+ if (isa<ReturnInst>(&Inst))
+ ReturnedValues.push_back(&Inst);
+
+ if (!hasUsefulEdges(&Inst))
+ return;
+
SmallVector<Edge, 8> Edges;
- for (auto &Bb : Fn->getBasicBlockList()) {
- for (auto &Inst : Bb.getInstList()) {
- // We don't want the edges of most "return" instructions, but we *do* want
- // to know what can be returned.
- if (auto *Ret = dyn_cast<ReturnInst>(&Inst))
- ReturnedValues.push_back(Ret);
+ argsToEdges(Analysis, &Inst, Edges);
- if (!hasUsefulEdges(&Inst))
- continue;
+ // In the case of an unused alloca (or similar), edges may be empty. Note
+ // that it exists so we can potentially answer NoAlias.
+ if (Edges.empty()) {
+ auto MaybeVal = getTargetValue(&Inst);
+ assert(MaybeVal.hasValue());
+ auto *Target = *MaybeVal;
+ findOrInsertNode(Target);
+ return;
+ }
+
+ const auto addEdgeToGraph = [&Graph, &findOrInsertNode](const Edge &E) {
+ auto To = findOrInsertNode(E.To);
+ auto From = findOrInsertNode(E.From);
+ auto FlippedWeight = flipWeight(E.Weight);
+ auto Attrs = E.AdditionalAttrs;
+ Graph.addEdge(From, To, std::make_pair(E.Weight, Attrs),
+ std::make_pair(FlippedWeight, Attrs));
+ };
- Edges.clear();
- argsToEdges(Analysis, &Inst, Edges);
+ SmallVector<ConstantExpr *, 4> ConstantExprs;
+ for (const Edge &E : Edges) {
+ addEdgeToGraph(E);
+ if (auto *Constexpr = dyn_cast<ConstantExpr>(E.To))
+ ConstantExprs.push_back(Constexpr);
+ if (auto *Constexpr = dyn_cast<ConstantExpr>(E.From))
+ ConstantExprs.push_back(Constexpr);
+ }
- // In the case of an unused alloca (or similar), edges may be empty. Note
- // that it exists so we can potentially answer NoAlias.
- if (Edges.empty()) {
- auto MaybeVal = getTargetValue(&Inst);
- assert(MaybeVal.hasValue());
- auto *Target = *MaybeVal;
- findOrInsertNode(Target);
- continue;
- }
+ for (ConstantExpr *CE : ConstantExprs) {
+ Edges.clear();
+ constexprToEdges(Analysis, *CE, Edges);
+ std::for_each(Edges.begin(), Edges.end(), addEdgeToGraph);
+ }
+}
- for (const Edge &E : Edges) {
- auto To = findOrInsertNode(E.To);
- auto From = findOrInsertNode(E.From);
- auto FlippedWeight = flipWeight(E.Weight);
- auto Attrs = E.AdditionalAttrs;
- Graph.addEdge(From, To, std::make_pair(E.Weight, Attrs),
- std::make_pair(FlippedWeight, Attrs));
- }
- }
+// Aside: We may remove graph construction entirely, because it doesn't really
+// buy us much that we don't already have. I'd like to add interprocedural
+// analysis prior to this however, in case that somehow requires the graph
+// produced by this for efficient execution
+static void buildGraphFrom(CFLAliasAnalysis &Analysis, Function *Fn,
+ SmallVectorImpl<Value *> &ReturnedValues,
+ NodeMapT &Map, GraphT &Graph) {
+ for (auto &Bb : Fn->getBasicBlockList())
+ for (auto &Inst : Bb.getInstList())
+ addInstructionToGraph(Analysis, Inst, ReturnedValues, Map, Graph);
+}
+
+static bool canSkipAddingToSets(Value *Val) {
+ // Constants can share instances, which may falsely unify multiple
+ // sets, e.g. in
+ // store i32* null, i32** %ptr1
+ // store i32* null, i32** %ptr2
+ // clearly ptr1 and ptr2 should not be unified into the same set, so
+ // we should filter out the (potentially shared) instance to
+ // i32* null.
+ if (isa<Constant>(Val)) {
+ bool Container = isa<ConstantVector>(Val) || isa<ConstantArray>(Val) ||
+ isa<ConstantStruct>(Val);
+ // TODO: Because all of these things are constant, we can determine whether
+ // the data is *actually* mutable at graph building time. This will probably
+ // come for free/cheap with offset awareness.
+ bool CanStoreMutableData =
+ isa<GlobalValue>(Val) || isa<ConstantExpr>(Val) || Container;
+ return !CanStoreMutableData;
}
+
+ return false;
}
static FunctionInfo buildSetsFrom(CFLAliasAnalysis &Analysis, Function *Fn) {
@@ -918,7 +1016,7 @@ static FunctionInfo buildSetsFrom(CFLAli
while (!Worklist.empty()) {
auto Node = Worklist.pop_back_val();
auto *CurValue = findValueOrDie(Node);
- if (isa<Constant>(CurValue) && !isa<GlobalValue>(CurValue))
+ if (canSkipAddingToSets(CurValue))
continue;
for (const auto &EdgeTuple : Graph.edgesFor(Node)) {
@@ -927,7 +1025,7 @@ static FunctionInfo buildSetsFrom(CFLAli
auto &OtherNode = std::get<1>(EdgeTuple);
auto *OtherValue = findValueOrDie(OtherNode);
- if (isa<Constant>(OtherValue) && !isa<GlobalValue>(OtherValue))
+ if (canSkipAddingToSets(OtherValue))
continue;
bool Added;
@@ -962,7 +1060,12 @@ static FunctionInfo buildSetsFrom(CFLAli
// things that were present during construction being present in the graph.
// So, we add all present arguments here.
for (auto &Arg : Fn->args()) {
- Builder.add(&Arg);
+ if (!Builder.add(&Arg))
+ continue;
+
+ auto Attrs = valueToAttrIndex(&Arg);
+ if (Attrs.hasValue())
+ Builder.noteAttributes(&Arg, *Attrs);
}
return FunctionInfo(Builder.build(), std::move(ReturnedValues));
Modified: llvm/trunk/test/Analysis/CFLAliasAnalysis/asm-global-bugfix.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Analysis/CFLAliasAnalysis/asm-global-bugfix.ll?rev=231743&r1=231742&r2=231743&view=diff
==============================================================================
--- llvm/trunk/test/Analysis/CFLAliasAnalysis/asm-global-bugfix.ll (original)
+++ llvm/trunk/test/Analysis/CFLAliasAnalysis/asm-global-bugfix.ll Mon Mar 9 21:58:15 2015
@@ -7,7 +7,7 @@
@G = private unnamed_addr constant [1 x i8] c"\00", align 1
; CHECK: Function: test_no_crash
-; CHECK: 1 no alias responses
+; CHECK: 0 no alias responses
define void @test_no_crash() #0 {
entry:
call i8* asm "nop", "=r,r"(
Modified: llvm/trunk/test/Analysis/CFLAliasAnalysis/const-expr-gep.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Analysis/CFLAliasAnalysis/const-expr-gep.ll?rev=231743&r1=231742&r2=231743&view=diff
==============================================================================
--- llvm/trunk/test/Analysis/CFLAliasAnalysis/const-expr-gep.ll (original)
+++ llvm/trunk/test/Analysis/CFLAliasAnalysis/const-expr-gep.ll Mon Mar 9 21:58:15 2015
@@ -7,15 +7,51 @@
%T = type { i32, [10 x i8] }
@G = external global %T
+ at G2 = external global %T
-; CHECK: Function: test
-; CHECK-NOT: May:
+; TODO: Quite a few of these are MayAlias because we don't yet consider
+; constant offsets in CFLAA. If we start doing so, then we'll need to
+; change these test cases
+; CHECK: Function: test
+; CHECK: MayAlias: i32* %D, i32* %F
+; CHECK: MayAlias: i32* %D, i8* %X
+; CHECK: MayAlias: i32* %F, i8* %X
define void @test() {
%D = getelementptr %T, %T* @G, i64 0, i32 0
- %E = getelementptr %T, %T* @G, i64 0, i32 1, i64 5
%F = getelementptr i32, i32* getelementptr (%T* @G, i64 0, i32 0), i64 0
%X = getelementptr [10 x i8], [10 x i8]* getelementptr (%T* @G, i64 0, i32 1), i64 0, i64 5
ret void
}
+
+; CHECK: Function: simplecheck
+; CHECK: MayAlias: i32* %F, i32* %arg0
+; CHECK: MayAlias: i32* %H, i32* %arg0
+; CHECK: MayAlias: i32* %F, i32* %H
+define void @simplecheck(i32* %arg0) {
+ %F = getelementptr i32, i32* getelementptr (%T* @G, i64 0, i32 0), i64 0
+ %H = getelementptr %T, %T* @G2, i64 0, i32 0
+
+ ret void
+}
+
+; Ensure that CFLAA properly identifies and handles escaping variables (i.e.
+; globals) in nested ConstantExprs
+
+; CHECK: Function: checkNesting
+; CHECK: MayAlias: i32* %A, i32* %arg0
+
+%NestedT = type { [1 x [1 x i32]] }
+ at NT = external global %NestedT
+
+define void @checkNesting(i32* %arg0) {
+ %A = getelementptr [1 x i32],
+ [1 x i32]* getelementptr
+ ([1 x [1 x i32]]* getelementptr (%NestedT* @NT, i64 0, i32 0),
+ i64 0,
+ i32 0),
+ i64 0,
+ i32 0
+ ret void
+}
Modified: llvm/trunk/test/Analysis/CFLAliasAnalysis/stratified-attrs-indexing.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Analysis/CFLAliasAnalysis/stratified-attrs-indexing.ll?rev=231743&r1=231742&r2=231743&view=diff
==============================================================================
--- llvm/trunk/test/Analysis/CFLAliasAnalysis/stratified-attrs-indexing.ll (original)
+++ llvm/trunk/test/Analysis/CFLAliasAnalysis/stratified-attrs-indexing.ll Mon Mar 9 21:58:15 2015
@@ -18,7 +18,7 @@ define void @test(i1 %cond,
i32* %arg31, i32* %arg32, i32* %arg33, i32* %arg34, i32* %arg35) {
; CHECK: 946 Total Alias Queries Performed
- ; CHECK: 810 no alias responses (85.6%)
+ ; CHECK: 43 no alias responses (4.5%)
%a = alloca i32, align 4
%b = select i1 %cond, i32* %arg35, i32* %arg34
%c = select i1 %cond, i32* %arg34, i32* %arg33
More information about the llvm-commits
mailing list