Teach basicaa about some stdc functions.

llvm-svn: 12408

lib/Analysis/BasicAliasAnalysis.cpp

@@ -21,13 +21,13 @@
 //===----------------------------------------------------------------------===//
 
 #include "llvm/Analysis/AliasAnalysis.h"
-#include "llvm/Pass.h"
+#include "llvm/Constants.h"
-#include "llvm/Argument.h"
+#include "llvm/DerivedTypes.h"
+#include "llvm/Function.h"
+#include "llvm/GlobalVariable.h"
 #include "llvm/iOther.h"
 #include "llvm/iMemory.h"
-#include "llvm/Constants.h"
+#include "llvm/Pass.h"
-#include "llvm/GlobalVariable.h"
-#include "llvm/DerivedTypes.h"
 #include "llvm/Target/TargetData.h"
 #include "llvm/Support/GetElementPtrTypeIterator.h"
 using namespace llvm;
@@ -53,6 +53,9 @@ namespace {
     /// global) or not.
     bool pointsToConstantMemory(const Value *P);
 
+    virtual bool doesNotAccessMemory(Function *F);
+    virtual bool onlyReadsMemory(Function *F);
+
   private:
     // CheckGEPInstructions - Check two GEP instructions with known
     // must-aliasing base pointers.  This checks to see if the index expressions
@@ -572,3 +575,95 @@ CheckGEPInstructions(const Type* BasePtr1Ty, std::vector<Value*> &GEP1Ops,
   return MayAlias;
 }
 
+namespace {
+  struct StringCompare {
+    bool operator()(const char *LHS, const char *RHS) {
+      return strcmp(LHS, RHS) < 0;
+    }
+  };
+}
+
+// Note that this list cannot contain libm functions (such as acos and sqrt)
+// that set errno on a domain or other error.
+static const char *DoesntAccessMemoryTable[] = {
+  "abs", "labs", "llabs", "imaxabs", "fabs", "fabsf", "fabsl",
+  "trunc", "truncf", "truncl", "ldexp",
+  
+  "atan", "atanf", "atanl",   "atan2", "atan2f", "atan2l",
+  "cbrt",
+  "cos", "cosf", "cosl",      "cosh", "coshf", "coshl",
+  "exp", "expf", "expl", 
+  "hypot",
+  "sin", "sinf", "sinl",      "sinh", "sinhf", "sinhl",
+  "tan", "tanf", "tanl",      "tanh", "tanhf", "tanhl",
+
+  "isalnum", "isalpha", "iscntrl", "isdigit", "isgraph", "islower", "isprint"
+  "ispunct", "isspace", "isupper", "isxdigit", "tolower", "toupper",
+
+  "iswalnum", "iswalpha", "iswcntrl", "iswdigit", "iswgraph", "iswlower",
+  "iswprint", "iswpunct", "iswspace", "iswupper", "iswxdigit",
+
+  "btowc", "wctob", 
+};
+
+static const unsigned DAMTableSize =
+    sizeof(DoesntAccessMemoryTable)/sizeof(DoesntAccessMemoryTable[0]);
+
+/// doesNotAccessMemory - Return true if we know that the function does not
+/// access memory at all.  Since basicaa does no analysis, we can only do simple
+/// things here.  In particular, if we have an external function with the name
+/// of a standard C library function, we are allowed to assume it will be
+/// resolved by libc, so we can hardcode some entries in here.
+bool BasicAliasAnalysis::doesNotAccessMemory(Function *F) {
+  if (!F->isExternal()) return false;
+
+  static bool Initialized = false;
+  if (!Initialized) {
+    // Sort the table the first time through.
+    std::sort(DoesntAccessMemoryTable, DoesntAccessMemoryTable+DAMTableSize,
+              StringCompare());
+    Initialized = true;
+  }
+
+  const char **Ptr = std::lower_bound(DoesntAccessMemoryTable,
+                                      DoesntAccessMemoryTable+DAMTableSize,
+                                      F->getName().c_str(), StringCompare());
+  return Ptr != DoesntAccessMemoryTable+DAMTableSize && *Ptr == F->getName();
+}
+
+
+static const char *OnlyReadsMemoryTable[] = {
+  "atoi", "atol", "atof", "atoll", "atoq",
+  "bcmp", "memcmp", "memchr", "wmemcmp", "wmemchr", 
+
+  // Strings
+  "strcmp", "strcasecmp", "strcoll", "strncmp", "strncasecmp",
+  "strchr", "strcspn", "strlen", "strpbrk", "strrchr", "strspn", "strstr", 
+
+  // Wide char strings
+  "wcschr", "wcscmp", "wcscoll", "wcscspn", "wcslen", "wcsncmp", "wcspbrk",
+  "wcsrchr", "wcsspn", "wcsstr", 
+};
+
+static const unsigned ORMTableSize =
+    sizeof(OnlyReadsMemoryTable)/sizeof(OnlyReadsMemoryTable[0]);
+
+bool BasicAliasAnalysis::onlyReadsMemory(Function *F) {
+  if (doesNotAccessMemory(F)) return true;
+  if (!F->isExternal()) return false;
+
+  static bool Initialized = false;
+  if (!Initialized) {
+    // Sort the table the first time through.
+    std::sort(OnlyReadsMemoryTable, OnlyReadsMemoryTable+ORMTableSize,
+              StringCompare());
+    Initialized = true;
+  }
+
+  const char **Ptr = std::lower_bound(OnlyReadsMemoryTable,
+                                      OnlyReadsMemoryTable+ORMTableSize,
+                                      F->getName().c_str(), StringCompare());
+  return Ptr != OnlyReadsMemoryTable+ORMTableSize && *Ptr == F->getName();
+}
+
+