simplify-libcalls: fold strstr(a, b) == a -> strncmp(a, b, strlen(b)) == 0

llvm-svn: 106047

llvm/include/llvm/Transforms/Utils/BuildLibCalls.h

@@ -34,6 +34,10 @@ namespace llvm {
   /// and the return value has 'i8*' type.
   Value *EmitStrChr(Value *Ptr, char C, IRBuilder<> &B, const TargetData *TD);
 
+  /// EmitStrNCmp - Emit a call to the strncmp function to the builder.
+  Value *EmitStrNCmp(Value *Ptr1, Value *Ptr2, Value *Len, IRBuilder<> &B,
+                     const TargetData *TD);
+
   /// EmitStrCpy - Emit a call to the strcpy function to the builder, for the
   /// specified pointer arguments.
   Value *EmitStrCpy(Value *Dst, Value *Src, IRBuilder<> &B,

llvm/lib/Transforms/Scalar/SimplifyLibCalls.cpp

@@ -92,6 +92,20 @@ static bool IsOnlyUsedInZeroEqualityComparison(Value *V) {
   return true;
 }
 
+/// IsOnlyUsedInEqualityComparison - Return true if it is only used in equality
+/// comparisons with With.
+static bool IsOnlyUsedInEqualityComparison(Value *V, Value *With) {
+  for (Value::use_iterator UI = V->use_begin(), E = V->use_end();
+       UI != E; ++UI) {
+    if (ICmpInst *IC = dyn_cast<ICmpInst>(*UI))
+      if (IC->isEquality() && IC->getOperand(1) == With)
+        continue;
+    // Unknown instruction.
+    return false;
+  }
+  return true;
+}
+
 //===----------------------------------------------------------------------===//
 // String and Memory LibCall Optimizations
 //===----------------------------------------------------------------------===//
@@ -503,6 +517,23 @@ struct StrStrOpt : public LibCallOptimization {
     if (CI->getOperand(1) == CI->getOperand(2))
       return B.CreateBitCast(CI->getOperand(1), CI->getType());
 
+    // fold strstr(a, b) == a -> strncmp(a, b, strlen(b)) == 0
+    if (TD && IsOnlyUsedInEqualityComparison(CI, CI->getOperand(1))) {
+      Value *StrLen = EmitStrLen(CI->getOperand(2), B, TD);
+      Value *StrNCmp = EmitStrNCmp(CI->getOperand(1), CI->getOperand(2),
+                                   StrLen, B, TD);
+      for (Value::use_iterator UI = CI->use_begin(), UE = CI->use_end();
+           UI != UE; ) {
+        ICmpInst *Old = cast<ICmpInst>(UI++);
+        Value *Cmp = B.CreateICmp(Old->getPredicate(), StrNCmp,
+                                  ConstantInt::getNullValue(StrNCmp->getType()),
+                                  "cmp");
+        Old->replaceAllUsesWith(Cmp);
+        Old->eraseFromParent();
+      }
+      return CI;
+    }
+
     // See if either input string is a constant string.
     std::string SearchStr, ToFindStr;
     bool HasStr1 = GetConstantStringInfo(CI->getOperand(1), SearchStr);

llvm/lib/Transforms/Utils/BuildLibCalls.cpp

@@ -69,6 +69,31 @@ Value *llvm::EmitStrChr(Value *Ptr, char C, IRBuilder<> &B,
   return CI;
 }
 
+/// EmitStrNCmp - Emit a call to the strncmp function to the builder.
+Value *llvm::EmitStrNCmp(Value *Ptr1, Value *Ptr2, Value *Len,
+                         IRBuilder<> &B, const TargetData *TD) {
+  Module *M = B.GetInsertBlock()->getParent()->getParent();
+  AttributeWithIndex AWI[3];
+  AWI[0] = AttributeWithIndex::get(1, Attribute::NoCapture);
+  AWI[1] = AttributeWithIndex::get(2, Attribute::NoCapture);
+  AWI[2] = AttributeWithIndex::get(~0u, Attribute::ReadOnly |
+                                   Attribute::NoUnwind);
+
+  LLVMContext &Context = B.GetInsertBlock()->getContext();
+  Value *StrNCmp = M->getOrInsertFunction("strncmp", AttrListPtr::get(AWI, 3),
+                                          B.getInt32Ty(),
+                                          B.getInt8PtrTy(),
+                                          B.getInt8PtrTy(),
+                                          TD->getIntPtrType(Context), NULL);
+  CallInst *CI = B.CreateCall3(StrNCmp, CastToCStr(Ptr1, B),
+                               CastToCStr(Ptr2, B), Len, "strncmp");
+
+  if (const Function *F = dyn_cast<Function>(StrNCmp->stripPointerCasts()))
+    CI->setCallingConv(F->getCallingConv());
+
+  return CI;
+}
+
 /// EmitStrCpy - Emit a call to the strcpy function to the builder, for the
 /// specified pointer arguments.
 Value *llvm::EmitStrCpy(Value *Dst, Value *Src, IRBuilder<> &B,

llvm/test/Transforms/SimplifyLibCalls/StrStr.ll

@@ -46,3 +46,15 @@ entry:
 ; CHECK: @test4
 ; CHECK: ret i8* %P
 }
+
+define i1 @test5(i8* %P, i8* %Q) nounwind readonly {
+entry:
+  %call = tail call i8* @strstr(i8* %P, i8* %Q) nounwind ; <i8*> [#uses=1]
+  %cmp = icmp eq i8* %call, %P
+  ret i1 %cmp
+; CHECK: @test5
+; CHECK: [[LEN:%[a-z]+]] = call {{i[0-9]+}} @strlen(i8* %Q)
+; CHECK: [[NCMP:%[a-z]+]] = call {{i[0-9]+}} @strncmp(i8* %P, i8* %Q, {{i[0-9]+}} [[LEN]])
+; CHECK: icmp eq {{i[0-9]+}} [[NCMP]], 0
+; CHECK: ret i1
+}