Add a new LibCallAliasAnalysis pass, which is parameterized

by an instance of LibCallInfo to provide mod/ref info of
standard library functions.  This is powerful enough to
say that 'sqrt' is readonly except that it modifies errno,
or that "printf doesn't store to memory unless the %n
constraint is present" etc.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@50827 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 169 insertions, 0 deletions

diff --git a/lib/Analysis/LibCallAliasAnalysis.cpp b/lib/Analysis/LibCallAliasAnalysis.cpp
new file mode 100644
index 0000000000..6492ac69b5
--- /dev/null
+++ b/lib/Analysis/LibCallAliasAnalysis.cpp
@@ -0,0 +1,169 @@
+//===- LibCallAliasAnalysis.cpp - Implement AliasAnalysis for libcalls ----===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// This file implements the LibCallAliasAnalysis class.
+//
+//===----------------------------------------------------------------------===//
+
+#include "llvm/Analysis/Passes.h"
+#include "llvm/Analysis/LibCallSemantics.h"
+#include "llvm/Function.h"
+#include "llvm/Pass.h"
+#include "llvm/Target/TargetData.h"
+using namespace llvm;
+
+namespace llvm {
+  /// LibCallAliasAnalysis - Alias analysis driven from LibCallInfo.
+  struct LibCallAliasAnalysis : public FunctionPass, AliasAnalysis {
+    static char ID; // Class identification
+    
+    LibCallInfo *LCI;
+    
+    LibCallAliasAnalysis(LibCallInfo *LC = 0)
+      : FunctionPass((intptr_t)&ID), LCI(LC) {
+    }
+    ~LibCallAliasAnalysis() {
+      delete LCI;
+    }
+    
+    ModRefResult getModRefInfo(CallSite CS, Value *P, unsigned Size);
+    ModRefResult getModRefInfo(CallSite CS1, CallSite CS2) {
+      // TODO: Could compare two direct calls against each other if we cared to.
+      return AliasAnalysis::getModRefInfo(CS1,CS2);
+    }
+    
+    virtual void getAnalysisUsage(AnalysisUsage &AU) const {
+      AliasAnalysis::getAnalysisUsage(AU);
+      AU.addRequired<TargetData>();
+      AU.setPreservesAll();                         // Does not transform code
+    }
+    
+    virtual bool runOnFunction(Function &F) {
+      InitializeAliasAnalysis(this);                 // set up super class
+      return false;
+    }
+    
+    /// hasNoModRefInfoForCalls - We can provide mod/ref information against
+    /// non-escaping allocations.
+    virtual bool hasNoModRefInfoForCalls() const { return false; }
+  private:
+    ModRefResult AnalyzeLibCallDetails(const LibCallFunctionInfo *FI,
+                                       CallSite CS, Value *P, unsigned Size);
+  };
+  
+  // Register this pass...
+  char LibCallAliasAnalysis::ID = 0;
+  RegisterPass<LibCallAliasAnalysis>
+  X("libcall-aa", "LibCall Alias Analysis", false, true);
+  
+  // Declare that we implement the AliasAnalysis interface
+  RegisterAnalysisGroup<AliasAnalysis> Y(X);
+}  // End of llvm namespace
+
+FunctionPass *llvm::createLibCallAliasAnalysisPass(LibCallInfo *LCI) {
+  return new LibCallAliasAnalysis(LCI);
+}
+
+
+/// AnalyzeLibCallDetails - Given a call to a function with the specified
+/// LibCallFunctionInfo, see if we can improve the mod/ref footprint of the call
+/// vs the specified pointer/size.
+AliasAnalysis::ModRefResult
+LibCallAliasAnalysis::AnalyzeLibCallDetails(const LibCallFunctionInfo *FI,
+                                            CallSite CS, Value *P,
+                                            unsigned Size) {
+  // If we have a function, check to see what kind of mod/ref effects it
+  // has.  Start by including any info globally known about the function.
+  AliasAnalysis::ModRefResult MRInfo = FI->UniversalBehavior;
+  if (MRInfo == NoModRef) return MRInfo;
+  
+  // If that didn't tell us that the function is 'readnone', check to see
+  // if we have detailed info and if 'P' is any of the locations we know
+  // about.
+  const LibCallFunctionInfo::LocationMRInfo *Details = FI->LocationDetails;
+  if (Details == 0)
+    return MRInfo;
+  
+  // If the details array is of the 'DoesNot' kind, we only know something if
+  // the pointer is a match for one of the locations in 'Details'.  If we find a
+  // match, we can prove some interactions cannot happen.
+  // 
+  if (FI->DetailsType == LibCallFunctionInfo::DoesNot) {
+    // Find out if the pointer refers to a known location.
+    for (unsigned i = 0; Details[i].LocationID != ~0U; ++i) {
+      const LibCallLocationInfo &Loc =
+      LCI->getLocationInfo(Details[i].LocationID);
+      LibCallLocationInfo::LocResult Res = Loc.isLocation(CS, P, Size);
+      if (Res != LibCallLocationInfo::Yes) continue;
+      
+      // If we find a match against a location that we 'do not' interact with,
+      // learn this info into MRInfo.
+      return ModRefResult(MRInfo & ~Details[i].MRInfo);
+    }
+    return MRInfo;
+  }
+  
+  // If the details are of the 'DoesOnly' sort, we know something if the pointer
+  // is a match for one of the locations in 'Details'.  Also, if we can prove
+  // that the pointers is *not* one of the locations in 'Details', we know that
+  // the call is NoModRef.
+  assert(FI->DetailsType == LibCallFunctionInfo::DoesOnly);
+  
+  // Find out if the pointer refers to a known location.
+  bool NoneMatch = true;
+  for (unsigned i = 0; Details[i].LocationID != ~0U; ++i) {
+    const LibCallLocationInfo &Loc =
+    LCI->getLocationInfo(Details[i].LocationID);
+    LibCallLocationInfo::LocResult Res = Loc.isLocation(CS, P, Size);
+    if (Res == LibCallLocationInfo::No) continue;
+    
+    // If we don't know if this pointer points to the location, then we have to
+    // assume it might alias in some case.
+    if (Res == LibCallLocationInfo::Unknown) {
+      NoneMatch = false;
+      continue;
+    }
+    
+    // If we know that this pointer definitely is pointing into the location,
+    // merge in this information.
+    return ModRefResult(MRInfo & Details[i].MRInfo);
+  }
+  
+  // If we found that the pointer is guaranteed to not match any of the
+  // locations in our 'DoesOnly' rule, then we know that the pointer must point
+  // to some other location.  Since the libcall doesn't mod/ref any other
+  // locations, return NoModRef.
+  if (NoneMatch)
+    return NoModRef;
+  
+  // Otherwise, return any other info gained so far.
+  return MRInfo;
+}
+
+// getModRefInfo - Check to see if the specified callsite can clobber the
+// specified memory object.
+//
+AliasAnalysis::ModRefResult
+LibCallAliasAnalysis::getModRefInfo(CallSite CS, Value *P, unsigned Size) {
+  ModRefResult MRInfo = ModRef;
+  
+  // If this is a direct call to a function that LCI knows about, get the
+  // information about the runtime function.
+  if (Function *F = CS.getCalledFunction()) {
+    if (LCI && F->isDeclaration()) {
+      if (const LibCallFunctionInfo *FI = LCI->getFunctionInfo(F)) {
+        MRInfo = ModRefResult(MRInfo & AnalyzeLibCallDetails(FI, CS, P, Size));
+        if (MRInfo == NoModRef) return NoModRef;
+      }
+    }
+  }
+  
+  // The AliasAnalysis base class has some smarts, lets use them.
+  return (ModRefResult)(MRInfo | AliasAnalysis::getModRefInfo(CS, P, Size));
+}