[PATCH] D14769: [FunctionAttrs] Calls to libcalls don't cause a function to potentially recurse

[James Molloy via llvm-commits]

jmolloy created this revision.
jmolloy added reviewers: joker.eph, manmanren, dexonsmith.
jmolloy added a subscriber: llvm-commits.
jmolloy set the repository for this revision to rL LLVM.

If a function calls a library function, that shouldn't be treated as potentially causing a cycle in the CFG. Additionally calls to noreturn functions are norecurse by definition.

Repository:
  rL LLVM

http://reviews.llvm.org/D14769

Files:
  lib/Transforms/IPO/FunctionAttrs.cpp
  test/Transforms/FunctionAttrs/norecurse.ll

Index: test/Transforms/FunctionAttrs/norecurse.ll
===================================================================
--- test/Transforms/FunctionAttrs/norecurse.ll
+++ test/Transforms/FunctionAttrs/norecurse.ll
@@ -1,5 +1,7 @@
 ; RUN: opt < %s -basicaa -functionattrs -S | FileCheck %s
 
+target triple = "x86_64-linux-gnu"
+
 ; CHECK: define i32 @leaf() #0
 define i32 @leaf() {
   ret i32 1
@@ -53,5 +55,24 @@
   ret void
 }
 
+; CHECK: define i32 @calls_exit() #2
+define i32 @calls_exit() {
+  call void @exit(i32 2)
+  ret i32 5
+}
+
+declare void @exit(i32) noreturn
+
+; CHECK: define i32 @calls_only_libcalls() #2
+define i32 @calls_only_libcalls() {
+  %a = call double @sin(double 0.0)
+  call void @fclose(i8* null)
+  ret i32 2
+}
+
+declare double @sin(double)
+declare void @fclose(i8*)
+
 ; CHECK: attributes #0 = { norecurse readnone }
 ; CHECK: attributes #1 = { readnone }
+; CHECK: attributes #2 = { norecurse }
\ No newline at end of file
Index: lib/Transforms/IPO/FunctionAttrs.cpp
===================================================================
--- lib/Transforms/IPO/FunctionAttrs.cpp
+++ lib/Transforms/IPO/FunctionAttrs.cpp
@@ -1795,6 +1795,7 @@
 }
 
 static bool addNoRecurseAttrs(const CallGraphSCC &SCC,
+                              const TargetLibraryInfo &TLI,
                               SmallVectorImpl<WeakVH> &Revisit) {
   // Try and identify functions that do not recurse.
 
@@ -1804,16 +1805,29 @@
 
   const CallGraphNode *CGN = *SCC.begin();
   Function *F = CGN->getFunction();
-  if (!F || F->isDeclaration() || F->doesNotRecurse())
+  if (!F || 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.
+  // A noreturn function by definition cannot recurse.
+  if (F->doesNotReturn())
+    return setDoesNotRecurse(*F);
+
+  if (F->isDeclaration())
+    return false;
+
+  auto IsLibCall = [&](Function *F) {
+    LibFunc::Func LF;
+    return TLI.getLibFunc(F->getName(), LF) && TLI.has(LF);
+  };
+
+  // If all of the calls in F are identifiable and are to norecurse functions or
+  // are libcalls, 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) {
+                  [&](const CallGraphNode::CallRecord &CR) {
                     Function *F = CR.second->getFunction();
-                    return F && F->doesNotRecurse();
+                    return F && (F->doesNotRecurse() || IsLibCall(F));
                   }))
     // Function calls a potentially recursive function.
     return setDoesNotRecurse(*F);
@@ -1890,8 +1904,8 @@
     Changed |= addNoAliasAttrs(SCCNodes);
     Changed |= addNonNullAttrs(SCCNodes, *TLI);
   }
-  
-  Changed |= addNoRecurseAttrs(SCC, Revisit);
+
+  Changed |= addNoRecurseAttrs(SCC, *TLI, Revisit);
   return Changed;
 }
 


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