[FunctionAttrs] Identify norecurse functions

A function can be marked as norecurse if:
  * The SCC to which it belongs has cardinality 1; and either
    a) It does not call any non-norecurse function. This includes self-recursion; or
    b) It only has one callsite and the function that callsite is within is marked norecurse.

a) is best propagated bottom-up and b) is best propagated top-down.

We build up the norecurse attributes bottom-up using the existing SCC pass, and mark functions with no obvious recursion (but not provably norecurse) to sweep later, top-down.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@252862 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/lib/Transforms/IPO/FunctionAttrs.cpp b/lib/Transforms/IPO/FunctionAttrs.cpp
index 351809ddedec6475dc961dc0a630c5218df8f46c..edebc26d475e53262b58aa71b7f3e304aa1c5908 100644 (file)
--- a/lib/Transforms/IPO/FunctionAttrs.cpp
+++ b/lib/Transforms/IPO/FunctionAttrs.cpp
@@ -50,6 +50,7 @@ STATISTIC(NumReadOnlyArg, "Number of arguments marked readonly");
 STATISTIC(NumNoAlias, "Number of function returns marked noalias");
 STATISTIC(NumNonNullReturn, "Number of function returns marked nonnull");
 STATISTIC(NumAnnotated, "Number of attributes added to library functions");
+STATISTIC(NumNoRecurse, "Number of functions marked as norecurse");
 
 namespace {
 typedef SmallSetVector<Function *, 8> SCCNodeSet;
@@ -63,7 +64,12 @@ struct FunctionAttrs : public CallGraphSCCPass {
   }
 
   bool runOnSCC(CallGraphSCC &SCC) override;
-
+  bool doInitialization(CallGraph &CG) override {
+    Revisit.clear();
+    return false;
+  }
+  bool doFinalization(CallGraph &CG) override;
+  
   void getAnalysisUsage(AnalysisUsage &AU) const override {
     AU.setPreservesCFG();
     AU.addRequired<AssumptionCacheTracker>();
@@ -73,6 +79,7 @@ struct FunctionAttrs : public CallGraphSCCPass {
 
 private:
   TargetLibraryInfo *TLI;
+  SmallVector<WeakVH,16> Revisit;
 };
 }
 
@@ -976,6 +983,14 @@ static void setDoesNotAlias(Function &F, unsigned n) {
   }
 }
 
+static bool setDoesNotRecurse(Function &F) {
+  if (F.doesNotRecurse())
+    return false;
+  F.setDoesNotRecurse();
+  ++NumNoRecurse;
+  return true;
+}
+
 /// Analyze the name and prototype of the given function and set any applicable
 /// attributes.
 ///
@@ -1779,6 +1794,55 @@ static bool inferPrototypeAttributes(Function &F, const TargetLibraryInfo &TLI)
   return true;
 }
 
+static bool addNoRecurseAttrs(const CallGraphSCC &SCC,
+                              SmallVectorImpl<WeakVH> &Revisit) {
+  // Try and identify functions that do not recurse.
+
+  // If the SCC contains multiple nodes we know for sure there is recursion.
+  if (!SCC.isSingular())
+    return false;
+
+  const CallGraphNode *CGN = *SCC.begin();
+  Function *F = CGN->getFunction();
+  if (!F || F->isDeclaration() || F->doesNotRecurse())
+    return false;
+
+  // If all of the calls in F are identifiable and are to norecurse functions, F
+  // is norecurse. This check also detects self-recursion as F is not currently
+  // marked norecurse, so any called from F to F will not be marked norecurse.
+  if (std::all_of(CGN->begin(), CGN->end(),
+                  [](const CallGraphNode::CallRecord &CR) {
+                    Function *F = CR.second->getFunction();
+                    return F && F->doesNotRecurse();
+                  }))
+    // Function calls a potentially recursive function.
+    return setDoesNotRecurse(*F);
+
+  // We know that F is not obviously recursive, but we haven't been able to
+  // prove that it doesn't actually recurse. Add it to the Revisit list to try
+  // again top-down later.
+  Revisit.push_back(F);
+  return false;
+}
+
+static bool addNoRecurseAttrsTopDownOnly(Function *F) {
+  // If F is internal and all uses are in norecurse functions, then F is also
+  // norecurse.
+  if (F->doesNotRecurse())
+    return false;
+  if (F->hasInternalLinkage()) {
+    for (auto *U : F->users())
+      if (auto *I = dyn_cast<Instruction>(U)) {
+        if (!I->getParent()->getParent()->doesNotRecurse())
+          return false;
+      } else {
+        return false;
+      }
+    return setDoesNotRecurse(*F);
+  }
+  return false;
+}
+
 bool FunctionAttrs::runOnSCC(CallGraphSCC &SCC) {
   TLI = &getAnalysis<TargetLibraryInfoWrapperPass>().getTLI();
   bool Changed = false;
@@ -1826,6 +1890,19 @@ bool FunctionAttrs::runOnSCC(CallGraphSCC &SCC) {
     Changed |= addNoAliasAttrs(SCCNodes);
     Changed |= addNonNullAttrs(SCCNodes, *TLI);
   }
+  
+  Changed |= addNoRecurseAttrs(SCC, Revisit);
+  return Changed;
+}
 
+bool FunctionAttrs::doFinalization(CallGraph &CG) {
+  bool Changed = false;
+  // When iterating over SCCs we visit functions in a bottom-up fashion. Some of
+  // the rules we have for identifying norecurse functions work best with a
+  // top-down walk, so look again at all the functions we previously marked as
+  // worth revisiting, in top-down order.
+  for (auto &F : reverse(Revisit))
+    if (F)
+      Changed |= addNoRecurseAttrsTopDownOnly(cast<Function>((Value*)F));
   return Changed;
 }

diff --git a/test/Analysis/TypeBasedAliasAnalysis/functionattrs.ll b/test/Analysis/TypeBasedAliasAnalysis/functionattrs.ll
index 6c9439afeeabbd205476e5a1acca0485da397f24..44031417032d2edeea5f677cd790efbc663c56ae 100644 (file)
--- a/test/Analysis/TypeBasedAliasAnalysis/functionattrs.ll
+++ b/test/Analysis/TypeBasedAliasAnalysis/functionattrs.ll
@@ -30,7 +30,7 @@ define void @test1_yes(i32* %p) nounwind {
   ret void
 }
 
-; CHECK: define void @test1_no(i32* %p) #1 {
+; CHECK: define void @test1_no(i32* %p) #3 {
 define void @test1_no(i32* %p) nounwind {
   call void @callee(i32* %p), !tbaa !2
   ret void
@@ -72,9 +72,11 @@ define i32 @test3_no(i8* %p) nounwind {
 declare void @callee(i32* %p) nounwind
 declare void @llvm.memcpy.p0i8.p0i8.i64(i8*, i8*, i64, i32, i1) nounwind
 
-; CHECK: attributes #0 = { nounwind readnone }
-; CHECK: attributes #1 = { nounwind }
+; CHECK: attributes #0 = { norecurse nounwind readnone }
+; CHECK: attributes #1 = { norecurse nounwind }
 ; CHECK: attributes #2 = { nounwind readonly }
+; CHECK: attributes #3 = { nounwind }
+; CHECK: attributes #4 = { nounwind argmemonly }
 
 ; Root note.
 !0 = !{ }

diff --git a/test/Transforms/FunctionAttrs/2008-09-03-ReadNone.ll b/test/Transforms/FunctionAttrs/2008-09-03-ReadNone.ll
index ca05d63743b5eaa3605ddcd58413b4bf67170de6..b62698a776fb5e226649ef419aa24408cd663cce 100644 (file)
--- a/test/Transforms/FunctionAttrs/2008-09-03-ReadNone.ll
+++ b/test/Transforms/FunctionAttrs/2008-09-03-ReadNone.ll
@@ -10,15 +10,16 @@ define i32 @f() {
        ret i32 %tmp
 }
 
-; CHECK: define i32 @g() #0
+; CHECK: define i32 @g() #1
 define i32 @g() readonly {
        ret i32 0
 }
 
-; CHECK: define i32 @h() #0
+; CHECK: define i32 @h() #1
 define i32 @h() readnone {
        %tmp = load i32, i32* @x                ; <i32> [#uses=1]
        ret i32 %tmp
 }
 
 ; CHECK: attributes #0 = { readnone }
+; CHECK: attributes #1 = { norecurse readnone }

diff --git a/test/Transforms/FunctionAttrs/2010-10-30-volatile.ll b/test/Transforms/FunctionAttrs/2010-10-30-volatile.ll
index 1a64a83938048833029365852a581a1a1f8d7f1c..23bb18e92b4cbef7441471f5dddaf08cacb65f3b 100644 (file)
--- a/test/Transforms/FunctionAttrs/2010-10-30-volatile.ll
+++ b/test/Transforms/FunctionAttrs/2010-10-30-volatile.ll
@@ -4,7 +4,9 @@
 @g = constant i32 1
 
 define void @foo() {
-; CHECK: void @foo() {
+; CHECK: void @foo() #0 {
   %tmp = load volatile i32, i32* @g
   ret void
 }
+
+; CHECK: attributes #0 = { norecurse }

diff --git a/test/Transforms/FunctionAttrs/atomic.ll b/test/Transforms/FunctionAttrs/atomic.ll
index bb867011cc2a9df3911612ff72b7731a45bc0b55..dd915a6027f2cdd903e73ab6055dddc2bac0093d 100644 (file)
--- a/test/Transforms/FunctionAttrs/atomic.ll
+++ b/test/Transforms/FunctionAttrs/atomic.ll
@@ -19,5 +19,5 @@ entry:
   ret i32 %r
 }
 
-; CHECK: attributes #0 = { readnone ssp uwtable }
-; CHECK: attributes #1 = { ssp uwtable }
+; CHECK: attributes #0 = { norecurse readnone ssp uwtable }
+; CHECK: attributes #1 = { norecurse ssp uwtable }

diff --git a/test/Transforms/FunctionAttrs/norecurse.ll b/test/Transforms/FunctionAttrs/norecurse.ll
new file mode 100644 (file)
index 0000000..4748119
--- /dev/null
+++ b/test/Transforms/FunctionAttrs/norecurse.ll
@@ -0,0 +1,57 @@
+; RUN: opt < %s -basicaa -functionattrs -S | FileCheck %s
+
+; CHECK: define i32 @leaf() #0
+define i32 @leaf() {
+  ret i32 1
+}
+
+; CHECK: define i32 @self_rec() #1
+define i32 @self_rec() {
+  %a = call i32 @self_rec()
+  ret i32 4
+}
+
+; CHECK: define i32 @indirect_rec() #1
+define i32 @indirect_rec() {
+  %a = call i32 @indirect_rec2()
+  ret i32 %a
+}
+; CHECK: define i32 @indirect_rec2() #1
+define i32 @indirect_rec2() {
+  %a = call i32 @indirect_rec()
+  ret i32 %a
+}
+
+; CHECK: define i32 @extern() #1
+define i32 @extern() {
+  %a = call i32 @k()
+  ret i32 %a
+}
+declare i32 @k() readnone
+
+; CHECK: define internal i32 @called_by_norecurse() #0
+define internal i32 @called_by_norecurse() {
+  %a = call i32 @k()
+  ret i32 %a
+}
+define void @m() norecurse {
+  %a = call i32 @called_by_norecurse()
+  ret void
+}
+
+; CHECK: define internal i32 @called_by_norecurse_indirectly() #0
+define internal i32 @called_by_norecurse_indirectly() {
+  %a = call i32 @k()
+  ret i32 %a
+}
+define internal void @o() {
+  %a = call i32 @called_by_norecurse_indirectly()
+  ret void
+}
+define void @p() norecurse {
+  call void @o()
+  ret void
+}
+
+; CHECK: attributes #0 = { norecurse readnone }
+; CHECK: attributes #1 = { readnone }

diff --git a/test/Transforms/FunctionAttrs/optnone.ll b/test/Transforms/FunctionAttrs/optnone.ll
index 7694bfe13aa519ea746bcfa9d92c021fa960439f..441ff4da65ecc991f04db46ef148b02ba36c9ce7 100644 (file)
--- a/test/Transforms/FunctionAttrs/optnone.ll
+++ b/test/Transforms/FunctionAttrs/optnone.ll
@@ -16,9 +16,11 @@ define void @test_optnone(i8* %p) noinline optnone {
 
 declare i8 @strlen(i8*) noinline optnone
 ; CHECK-LABEL: @strlen
-; CHECK: (i8*) #1
+; CHECK: (i8*) #2
 
 ; CHECK-LABEL: attributes #0
-; CHECK: = { readnone }
+; CHECK: = { norecurse readnone }
 ; CHECK-LABEL: attributes #1
+; CHECK: = { noinline norecurse optnone }
+; CHECK-LABEL: attributes #2
 ; CHECK: = { noinline optnone }