[DAGCombiner] Slice a big load in two loads when the element are next to each

[oota-llvm.git] / include / llvm / Target / TargetLowering.h

diff --git a/include/llvm/Target/TargetLowering.h b/include/llvm/Target/TargetLowering.h
index cd95a732234fa9e392e86c148b1a20c81a95eeb4..1c0ad63ac6191dea8ff774f310897ed5ff69eb8f 100644 (file)
--- a/include/llvm/Target/TargetLowering.h
+++ b/include/llvm/Target/TargetLowering.h
@@ -1183,6 +1183,35 @@ public:
     return false;
   }
 
+  /// Return true if the target supplies and combines to a paired load
+  /// two loaded values of type LoadedType next to each other in memory.
+  /// RequiredAlignment gives the minimal alignment constraints that must be met to
+  /// be able to select this paired load.
+  ///
+  /// This information is *not* used to generate actual paired loads, but it is used
+  /// to generate a sequence of loads that is easier to combine into a paired load.
+  /// For instance, something like this:
+  /// a = load i64* addr
+  /// b = trunc i64 a to i32
+  /// c = lshr i64 a, 32
+  /// d = trunc i64 c to i32
+  /// will be optimized into:
+  /// b = load i32* addr1
+  /// d = load i32* addr2
+  /// Where addr1 = addr2 +/- sizeof(i32).
+  ///
+  /// In other words, unless the target performs a post-isel load combining, this 
+  /// information should not be provided because it will generate more loads.
+  virtual bool hasPairedLoad(Type * /*LoadedType*/,
+                             unsigned & /*RequiredAligment*/) const {
+    return false;
+  }
+
+  virtual bool hasPairedLoad(EVT /*LoadedType*/,
+                             unsigned & /*RequiredAligment*/) const {
+    return false;
+  }
+
   /// Return true if zero-extending the specific node Val to type VT2 is free
   /// (either because it's implicitly zero-extended such as ARM ldrb / ldrh or
   /// because it's folded such as X86 zero-extending loads).
@@ -1473,10 +1502,12 @@ public:
     if (NumElts == 1)
       return LegalizeKind(TypeScalarizeVector, EltVT);
 
-    // Try to widen vector elements until a legal type is found.
+    // Try to widen vector elements until the element type is a power of two and 
+    // promote it to a legal type later on, for example:
+    // <3 x i8> -> <4 x i8> -> <4 x i32>
     if (EltVT.isInteger()) {
       // Vectors with a number of elements that is not a power of two are always
-      // widened, for example <3 x float> -> <4 x float>.
+      // widened, for example <3 x i8> -> <4 x i8>.
       if (!VT.isPow2VectorType()) {
         NumElts = (unsigned)NextPowerOf2(NumElts);
         EVT NVT = EVT::getVectorVT(Context, EltVT, NumElts);