<div dir="rtl"><div dir="ltr">This may be breaking the Visual C++ builders:</div><div dir="ltr"><br></div><div dir="ltr"> <a href="http://lab.llvm.org:8011/builders/lldb-x86-win7-msvc/builds/8864/steps/build/logs/stdio">http://lab.llvm.org:8011/builders/lldb-x86-win7-msvc/builds/8864/steps/build/logs/stdio</a><br></div><div dir="ltr"><br></div><div dir="ltr">dbgs() requiring llvm/Support/raw_ostream.h.</div><div dir="ltr"><br></div><div dir="ltr"><br></div></div><div class="gmail_extra"><br><div class="gmail_quote"><div dir="ltr">2015-08-31 22:44 GMT+03:00 Philip Reames via llvm-commits <span dir="ltr"><<a href="mailto:llvm-commits@lists.llvm.org" target="_blank">llvm-commits@lists.llvm.org</a>></span>:</div><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">Author: reames<br>
Date: Mon Aug 31 14:44:38 2015<br>
New Revision: 246476<br>
<br>
URL: <a href="http://llvm.org/viewvc/llvm-project?rev=246476&view=rev" rel="noreferrer" target="_blank">http://llvm.org/viewvc/llvm-project?rev=246476&view=rev</a><br>
Log:<br>
[FunctionAttr] Infer nonnull attributes on returns<br>
<br>
Teach FunctionAttr to infer the nonnull attribute on return values of functions which never return a potentially null value. This is done both via a conservative local analysis for the function itself and a optimistic per-SCC analysis. If no function in the SCC returns anything which could be null (other than values from other functions in the SCC), we can conclude no function returned a null pointer. Even if some function within the SCC returns a null pointer, we may be able to locally conclude that some don't.<br>
<br>
Differential Revision: <a href="http://reviews.llvm.org/D9688" rel="noreferrer" target="_blank">http://reviews.llvm.org/D9688</a><br>
<br>
<br>
Added:<br>
llvm/trunk/test/Transforms/FunctionAttrs/nonnull.ll<br>
Modified:<br>
llvm/trunk/lib/Transforms/IPO/FunctionAttrs.cpp<br>
<br>
Modified: llvm/trunk/lib/Transforms/IPO/FunctionAttrs.cpp<br>
URL: <a href="http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/IPO/FunctionAttrs.cpp?rev=246476&r1=246475&r2=246476&view=diff" rel="noreferrer" target="_blank">http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/IPO/FunctionAttrs.cpp?rev=246476&r1=246475&r2=246476&view=diff</a><br>
==============================================================================<br>
--- llvm/trunk/lib/Transforms/IPO/FunctionAttrs.cpp (original)<br>
+++ llvm/trunk/lib/Transforms/IPO/FunctionAttrs.cpp Mon Aug 31 14:44:38 2015<br>
@@ -27,10 +27,12 @@<br>
#include "llvm/Analysis/CallGraph.h"<br>
#include "llvm/Analysis/CallGraphSCCPass.h"<br>
#include "llvm/Analysis/CaptureTracking.h"<br>
+#include "llvm/Analysis/ValueTracking.h"<br>
#include "llvm/IR/GlobalVariable.h"<br>
#include "llvm/IR/InstIterator.h"<br>
#include "llvm/IR/IntrinsicInst.h"<br>
#include "llvm/IR/LLVMContext.h"<br>
+#include "llvm/Support/Debug.h"<br>
#include "llvm/Analysis/TargetLibraryInfo.h"<br>
using namespace llvm;<br>
<br>
@@ -42,6 +44,7 @@ STATISTIC(NumNoCapture, "Number of argum<br>
STATISTIC(NumReadNoneArg, "Number of arguments marked readnone");<br>
STATISTIC(NumReadOnlyArg, "Number of arguments marked readonly");<br>
STATISTIC(NumNoAlias, "Number of function returns marked noalias");<br>
+STATISTIC(NumNonNullReturn, "Number of function returns marked nonnull");<br>
STATISTIC(NumAnnotated, "Number of attributes added to library functions");<br>
<br>
namespace {<br>
@@ -67,6 +70,13 @@ namespace {<br>
// AddNoAliasAttrs - Deduce noalias attributes for the SCC.<br>
bool AddNoAliasAttrs(const CallGraphSCC &SCC);<br>
<br>
+ /// \brief Does this function return null?<br>
+ bool ReturnsNonNull(Function *F, SmallPtrSet<Function*, 8> &,<br>
+ bool &Speculative) const;<br>
+<br>
+ /// \brief Deduce nonnull attributes for the SCC.<br>
+ bool AddNonNullAttrs(const CallGraphSCC &SCC);<br>
+<br>
// Utility methods used by inferPrototypeAttributes to add attributes<br>
// and maintain annotation statistics.<br>
<br>
@@ -832,6 +842,143 @@ bool FunctionAttrs::AddNoAliasAttrs(cons<br>
return MadeChange;<br>
}<br>
<br>
+bool FunctionAttrs::ReturnsNonNull(Function *F,<br>
+ SmallPtrSet<Function*, 8> &SCCNodes,<br>
+ bool &Speculative) const {<br>
+ assert(F->getReturnType()->isPointerTy() &&<br>
+ "nonnull only meaningful on pointer types");<br>
+ Speculative = false;<br>
+<br>
+ SmallSetVector<Value *, 8> FlowsToReturn;<br>
+ for (BasicBlock &BB : *F)<br>
+ if (auto *Ret = dyn_cast<ReturnInst>(BB.getTerminator()))<br>
+ FlowsToReturn.insert(Ret->getReturnValue());<br>
+<br>
+ for (unsigned i = 0; i != FlowsToReturn.size(); ++i) {<br>
+ Value *RetVal = FlowsToReturn[i];<br>
+<br>
+ // If this value is locally known to be non-null, we're good<br>
+ if (isKnownNonNull(RetVal, TLI))<br>
+ continue;<br>
+<br>
+ // Otherwise, we need to look upwards since we can't make any local<br>
+ // conclusions.<br>
+ Instruction *RVI = dyn_cast<Instruction>(RetVal);<br>
+ if (!RVI)<br>
+ return false;<br>
+ switch (RVI->getOpcode()) {<br>
+ // Extend the analysis by looking upwards.<br>
+ case Instruction::BitCast:<br>
+ case Instruction::GetElementPtr:<br>
+ case Instruction::AddrSpaceCast:<br>
+ FlowsToReturn.insert(RVI->getOperand(0));<br>
+ continue;<br>
+ case Instruction::Select: {<br>
+ SelectInst *SI = cast<SelectInst>(RVI);<br>
+ FlowsToReturn.insert(SI->getTrueValue());<br>
+ FlowsToReturn.insert(SI->getFalseValue());<br>
+ continue;<br>
+ }<br>
+ case Instruction::PHI: {<br>
+ PHINode *PN = cast<PHINode>(RVI);<br>
+ for (int i = 0, e = PN->getNumIncomingValues(); i != e; ++i)<br>
+ FlowsToReturn.insert(PN->getIncomingValue(i));<br>
+ continue;<br>
+ }<br>
+ case Instruction::Call:<br>
+ case Instruction::Invoke: {<br>
+ CallSite CS(RVI);<br>
+ Function *Callee = CS.getCalledFunction();<br>
+ // A call to a node within the SCC is assumed to return null until<br>
+ // proven otherwise<br>
+ if (Callee && SCCNodes.count(Callee)) {<br>
+ Speculative = true;<br>
+ continue;<br>
+ }<br>
+ return false;<br>
+ }<br>
+ default:<br>
+ return false; // Unknown source, may be null<br>
+ };<br>
+ llvm_unreachable("should have either continued or returned");<br>
+ }<br>
+<br>
+ return true;<br>
+}<br>
+<br>
+bool FunctionAttrs::AddNonNullAttrs(const CallGraphSCC &SCC) {<br>
+ SmallPtrSet<Function*, 8> SCCNodes;<br>
+<br>
+ // Fill SCCNodes with the elements of the SCC. Used for quickly<br>
+ // looking up whether a given CallGraphNode is in this SCC.<br>
+ for (CallGraphSCC::iterator I = SCC.begin(), E = SCC.end(); I != E; ++I)<br>
+ SCCNodes.insert((*I)->getFunction());<br>
+<br>
+ // Speculative that all functions in the SCC return only nonnull<br>
+ // pointers. We may refute this as we analyze functions.<br>
+ bool SCCReturnsNonNull = true;<br>
+<br>
+ bool MadeChange = false;<br>
+<br>
+ // Check each function in turn, determining which functions return nonnull<br>
+ // pointers.<br>
+ for (CallGraphSCC::iterator I = SCC.begin(), E = SCC.end(); I != E; ++I) {<br>
+ Function *F = (*I)->getFunction();<br>
+<br>
+ if (!F || F->hasFnAttribute(Attribute::OptimizeNone))<br>
+ // External node or node we don't want to optimize - skip it;<br>
+ return false;<br>
+<br>
+ // Already nonnull.<br>
+ if (F->getAttributes().hasAttribute(AttributeSet::ReturnIndex,<br>
+ Attribute::NonNull))<br>
+ continue;<br>
+<br>
+ // Definitions with weak linkage may be overridden at linktime, so<br>
+ // treat them like declarations.<br>
+ if (F->isDeclaration() || F->mayBeOverridden())<br>
+ return false;<br>
+<br>
+ // We annotate nonnull return values, which are only applicable to<br>
+ // pointer types.<br>
+ if (!F->getReturnType()->isPointerTy())<br>
+ continue;<br>
+<br>
+ bool Speculative = false;<br>
+ if (ReturnsNonNull(F, SCCNodes, Speculative)) {<br>
+ if (!Speculative) {<br>
+ // Mark the function eagerly since we may discover a function<br>
+ // which prevents us from speculating about the entire SCC<br>
+ DEBUG(dbgs() << "Eagerly marking " << F->getName() << " as nonnull\n");<br>
+ F->addAttribute(AttributeSet::ReturnIndex, Attribute::NonNull);<br>
+ ++NumNonNullReturn;<br>
+ MadeChange = true;<br>
+ }<br>
+ continue;<br>
+ }<br>
+ // At least one function returns something which could be null, can't<br>
+ // speculate any more.<br>
+ SCCReturnsNonNull = false;<br>
+ }<br>
+<br>
+ if (SCCReturnsNonNull) {<br>
+ for (CallGraphSCC::iterator I = SCC.begin(), E = SCC.end(); I != E; ++I) {<br>
+ Function *F = (*I)->getFunction();<br>
+ if (F->getAttributes().hasAttribute(AttributeSet::ReturnIndex,<br>
+ Attribute::NonNull) ||<br>
+ !F->getReturnType()->isPointerTy())<br>
+ continue;<br>
+<br>
+ DEBUG(dbgs() << "SCC marking " << F->getName() << " as nonnull\n");<br>
+ F->addAttribute(AttributeSet::ReturnIndex, Attribute::NonNull);<br>
+ ++NumNonNullReturn;<br>
+ MadeChange = true;<br>
+ }<br>
+ }<br>
+<br>
+ return MadeChange;<br>
+}<br>
+<br>
/// inferPrototypeAttributes - Analyze the name and prototype of the<br>
/// given function and set any applicable attributes. Returns true<br>
/// if any attributes were set and false otherwise.<br>
@@ -1707,5 +1854,6 @@ bool FunctionAttrs::runOnSCC(CallGraphSC<br>
Changed |= AddReadAttrs(SCC);<br>
Changed |= AddArgumentAttrs(SCC);<br>
Changed |= AddNoAliasAttrs(SCC);<br>
+ Changed |= AddNonNullAttrs(SCC);<br>
return Changed;<br>
}<br>
<br>
Added: llvm/trunk/test/Transforms/FunctionAttrs/nonnull.ll<br>
URL: <a href="http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/FunctionAttrs/nonnull.ll?rev=246476&view=auto" rel="noreferrer" target="_blank">http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/FunctionAttrs/nonnull.ll?rev=246476&view=auto</a><br>
==============================================================================<br>
--- llvm/trunk/test/Transforms/FunctionAttrs/nonnull.ll (added)<br>
+++ llvm/trunk/test/Transforms/FunctionAttrs/nonnull.ll Mon Aug 31 14:44:38 2015<br>
@@ -0,0 +1,74 @@<br>
+; RUN: opt -S -functionattrs %s | FileCheck %s<br>
+declare nonnull i8* @ret_nonnull()<br>
+<br>
+; Return a pointer trivially nonnull (call return attribute)<br>
+define i8* @test1() {<br>
+; CHECK: define nonnull i8* @test1<br>
+ %ret = call i8* @ret_nonnull()<br>
+ ret i8* %ret<br>
+}<br>
+<br>
+; Return a pointer trivially nonnull (argument attribute)<br>
+define i8* @test2(i8* nonnull %p) {<br>
+; CHECK: define nonnull i8* @test2<br>
+ ret i8* %p<br>
+}<br>
+<br>
+; Given an SCC where one of the functions can not be marked nonnull,<br>
+; can we still mark the other one which is trivially nonnull<br>
+define i8* @scc_binder() {<br>
+; CHECK: define i8* @scc_binder<br>
+ call i8* @test3()<br>
+ ret i8* null<br>
+}<br>
+<br>
+define i8* @test3() {<br>
+; CHECK: define nonnull i8* @test3<br>
+ call i8* @scc_binder()<br>
+ %ret = call i8* @ret_nonnull()<br>
+ ret i8* %ret<br>
+}<br>
+<br>
+; Given a mutual recursive set of functions, we can mark them<br>
+; nonnull if neither can ever return null. (In this case, they<br>
+; just never return period.)<br>
+define i8* @test4_helper() {<br>
+; CHECK: define noalias nonnull i8* @test4_helper<br>
+ %ret = call i8* @test4()<br>
+ ret i8* %ret<br>
+}<br>
+<br>
+define i8* @test4() {<br>
+; CHECK: define noalias nonnull i8* @test4<br>
+ %ret = call i8* @test4_helper()<br>
+ ret i8* %ret<br>
+}<br>
+<br>
+; Given a mutual recursive set of functions which *can* return null<br>
+; make sure we haven't marked them as nonnull.<br>
+define i8* @test5_helper() {<br>
+; CHECK: define noalias i8* @test5_helper<br>
+ %ret = call i8* @test5()<br>
+ ret i8* null<br>
+}<br>
+<br>
+define i8* @test5() {<br>
+; CHECK: define noalias i8* @test5<br>
+ %ret = call i8* @test5_helper()<br>
+ ret i8* %ret<br>
+}<br>
+<br>
+; Local analysis, but going through a self recursive phi<br>
+define i8* @test6() {<br>
+entry:<br>
+; CHECK: define nonnull i8* @test6<br>
+ %ret = call i8* @ret_nonnull()<br>
+ br label %loop<br>
+loop:<br>
+ %phi = phi i8* [%ret, %entry], [%phi, %loop]<br>
+ br i1 undef, label %loop, label %exit<br>
+exit:<br>
+ ret i8* %phi<br>
+}<br>
+<br>
+<br>
<br>
<br>
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</blockquote></div><br></div>