handle equality memcmp of 8 bytes on x86-64 with two unaligned loads and a

compare.  On other targets we end up with a call to memcmp because we don't
want 16 individual byte loads.  We should be able to use movups as well, but
we're failing to select the generated icmp.



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@92107 91177308-0d34-0410-b5e6-96231b3b80d8

lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp

@@ -5092,17 +5092,8 @@ static bool IsOnlyUsedInZeroEqualityComparison(Value *V) {
   return true;
 }
 
-static SDValue getMemCmpLoad(Value *PtrVal, unsigned Size,
+static SDValue getMemCmpLoad(Value *PtrVal, MVT LoadVT, const Type *LoadTy,
                              SelectionDAGBuilder &Builder) {
-  MVT LoadVT;
-  const Type *LoadTy;
-  if (Size == 2) {
-    LoadVT = MVT::i16;
-    LoadTy = Type::getInt16Ty(PtrVal->getContext());
-  } else {
-    LoadVT = MVT::i32;
-    LoadTy = Type::getInt32Ty(PtrVal->getContext()); 
-  }
   
   // Check to see if this load can be trivially constant folded, e.g. if the
   // input is from a string literal.
@@ -5158,10 +5149,54 @@ bool SelectionDAGBuilder::visitMemCmpCall(CallInst &I) {
   
   // memcmp(S1,S2,2) != 0 -> (*(short*)LHS != *(short*)RHS)  != 0
   // memcmp(S1,S2,4) != 0 -> (*(int*)LHS != *(int*)RHS)  != 0
-  if (Size && (Size->getValue() == 2 || Size->getValue() == 4) &&
+  if (Size && IsOnlyUsedInZeroEqualityComparison(&I)) {
-      IsOnlyUsedInZeroEqualityComparison(&I)) {
+    bool ActuallyDoIt = true;
-    SDValue LHSVal = getMemCmpLoad(LHS, Size->getZExtValue(), *this);
+    MVT LoadVT;
-    SDValue RHSVal = getMemCmpLoad(RHS, Size->getZExtValue(), *this);
+    const Type *LoadTy;
+    switch (Size->getZExtValue()) {
+    default:
+      LoadVT = MVT::Other;
+      LoadTy = 0;
+      ActuallyDoIt = false;
+      break;
+    case 2:
+      LoadVT = MVT::i16;
+      LoadTy = Type::getInt16Ty(Size->getContext());
+      break;
+    case 4:
+      LoadVT = MVT::i32;
+      LoadTy = Type::getInt32Ty(Size->getContext()); 
+      break;
+    case 8:
+      LoadVT = MVT::i64;
+      LoadTy = Type::getInt64Ty(Size->getContext()); 
+      break;
+        /*
+    case 16:
+      LoadVT = MVT::v4i32;
+      LoadTy = Type::getInt32Ty(Size->getContext()); 
+      LoadTy = VectorType::get(LoadTy, 4);
+      break;
+         */
+    }
+    
+    // This turns into unaligned loads.  We only do this if the target natively
+    // supports the MVT we'll be loading or if it is small enough (<= 4) that
+    // we'll only produce a small number of byte loads.
+    
+    // Require that we can find a legal MVT, and only do this if the target
+    // supports unaligned loads of that type.  Expanding into byte loads would
+    // bloat the code.
+    if (ActuallyDoIt && Size->getZExtValue() > 4) {
+      // TODO: Handle 5 byte compare as 4-byte + 1 byte.
+      // TODO: Handle 8 byte compare on x86-32 as two 32-bit loads.
+      if (!TLI.isTypeLegal(LoadVT) ||!TLI.allowsUnalignedMemoryAccesses(LoadVT))
+        ActuallyDoIt = false;
+    }
+    
+    if (ActuallyDoIt) {
+      SDValue LHSVal = getMemCmpLoad(LHS, LoadVT, LoadTy, *this);
+      SDValue RHSVal = getMemCmpLoad(RHS, LoadVT, LoadTy, *this);
       
       SDValue Res = DAG.getSetCC(getCurDebugLoc(), MVT::i1, LHSVal, RHSVal,
                                  ISD::SETNE);
@@ -5169,6 +5204,7 @@ bool SelectionDAGBuilder::visitMemCmpCall(CallInst &I) {
       setValue(&I, DAG.getZExtOrTrunc(Res, getCurDebugLoc(), CallVT));
       return true;
     }
+  }
   
   
   return false;

test/CodeGen/X86/memcmp.ll

@@ -3,7 +3,7 @@
 ; This tests codegen time inlining/optimization of memcmp
 ; rdar://6480398
 
-@.str = private constant [6 x i8] c"fooxx\00", align 1 ; <[6 x i8]*> [#uses=1]
+@.str = private constant [23 x i8] c"fooooooooooooooooooooo\00", align 1 ; <[23 x i8]*> [#uses=1]
 
 declare i32 @memcmp(...)
 
@@ -26,7 +26,7 @@ return:                                           ; preds = %entry
 
 define void @memcmp2a(i8* %X, i32* nocapture %P) nounwind {
 entry:
-  %0 = tail call i32 (...)* @memcmp(i8* %X, i8* getelementptr inbounds ([6 x i8]* @.str, i32 0, i32 1), i32 2) nounwind ; <i32> [#uses=1]
+  %0 = tail call i32 (...)* @memcmp(i8* %X, i8* getelementptr inbounds ([23 x i8]* @.str, i32 0, i32 1), i32 2) nounwind ; <i32> [#uses=1]
   %1 = icmp eq i32 %0, 0                          ; <i1> [#uses=1]
   br i1 %1, label %return, label %bb
 
@@ -60,7 +60,7 @@ return:                                           ; preds = %entry
 
 define void @memcmp4a(i8* %X, i32* nocapture %P) nounwind {
 entry:
-  %0 = tail call i32 (...)* @memcmp(i8* %X, i8* getelementptr inbounds ([6 x i8]* @.str, i32 0, i32 1), i32 4) nounwind ; <i32> [#uses=1]
+  %0 = tail call i32 (...)* @memcmp(i8* %X, i8* getelementptr inbounds ([23 x i8]* @.str, i32 0, i32 1), i32 4) nounwind ; <i32> [#uses=1]
   %1 = icmp eq i32 %0, 0                          ; <i1> [#uses=1]
   br i1 %1, label %return, label %bb
 
@@ -71,6 +71,40 @@ bb:                                               ; preds = %entry
 return:                                           ; preds = %entry
   ret void
 ; CHECK: memcmp4a:
-; CHECK: cmpl $2021158767, (%rdi)
+; CHECK: cmpl $1869573999, (%rdi)
+}
+
+define void @memcmp8(i8* %X, i8* %Y, i32* nocapture %P) nounwind {
+entry:
+  %0 = tail call i32 (...)* @memcmp(i8* %X, i8* %Y, i32 8) nounwind ; <i32> [#uses=1]
+  %1 = icmp eq i32 %0, 0                          ; <i1> [#uses=1]
+  br i1 %1, label %return, label %bb
+
+bb:                                               ; preds = %entry
+  store i32 4, i32* %P, align 4
+  ret void
+
+return:                                           ; preds = %entry
+  ret void
+; CHECK: memcmp8:
+; CHECK: movq    (%rsi), %rax
+; CHECK: cmpq    %rax, (%rdi)
+}
+
+define void @memcmp8a(i8* %X, i32* nocapture %P) nounwind {
+entry:
+  %0 = tail call i32 (...)* @memcmp(i8* %X, i8* getelementptr inbounds ([23 x i8]* @.str, i32 0, i32 0), i32 8) nounwind ; <i32> [#uses=1]
+  %1 = icmp eq i32 %0, 0                          ; <i1> [#uses=1]
+  br i1 %1, label %return, label %bb
+
+bb:                                               ; preds = %entry
+  store i32 4, i32* %P, align 4
+  ret void
+
+return:                                           ; preds = %entry
+  ret void
+; CHECK: memcmp8a:
+; CHECK: movabsq $8029759185026510694, %rax
+; CHECK: cmpq	%rax, (%rdi)
 }