rdar://12100355 (part 1)

This revision attempts to recognize following population-count pattern:

 while(a) { c++; ... ; a &= a - 1; ... },
  where <c> and <a>could be used multiple times in the loop body.

 TODO: On X8664 and ARM, __buildin_ctpop() are not expanded to a efficent 
instruction sequence, which need to be improved in the following commits.

Reviewed by Nadav, really appreciate!


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@168931 91177308-0d34-0410-b5e6-96231b3b80d8

2 files changed, 18 insertions, 1 deletions

diff --git a/include/llvm/Target/TargetTransformImpl.h b/include/llvm/Target/TargetTransformImpl.h
index 7ea2396076..ad38eaf95f 100644
--- a/include/llvm/Target/TargetTransformImpl.h
+++ b/include/llvm/Target/TargetTransformImpl.h
@@ -26,7 +26,7 @@ class TargetLowering;
 /// ScalarTargetTransformInfo interface. Different targets can implement
 /// this interface differently.
 class ScalarTargetTransformImpl : public ScalarTargetTransformInfo {
-private:
+protected:
   const TargetLowering *TLI;
 
 public:
diff --git a/include/llvm/TargetTransformInfo.h b/include/llvm/TargetTransformInfo.h
index 94db490443..dbe35ec4c3 100644
--- a/include/llvm/TargetTransformInfo.h
+++ b/include/llvm/TargetTransformInfo.h
@@ -75,6 +75,18 @@ public:
 /// LSR, and LowerInvoke use this interface.
 class ScalarTargetTransformInfo {
 public:
+  /// PopcntHwSupport - Hardware support for population count. Compared to the
+  /// SW implementation, HW support is supposed to significantly boost the
+  /// performance when the population is dense, and it may or not may degrade
+  /// performance if the population is sparse. A HW support is considered as
+  /// "Fast" if it can outperform, or is on a par with, SW implementaion when
+  /// the population is sparse; otherwise, it is considered as "Slow".
+  enum PopcntHwSupport {
+    None,
+    Fast,
+    Slow
+  };
+
   virtual ~ScalarTargetTransformInfo() {}
 
   /// isLegalAddImmediate - Return true if the specified immediate is legal
@@ -122,6 +134,11 @@ public:
   virtual bool shouldBuildLookupTables() const {
     return true;
   }
+
+  /// getPopcntHwSupport - Return hardware support for population count.
+  virtual PopcntHwSupport getPopcntHwSupport(unsigned IntTyWidthInBit) const {
+    return None;
+  }
 };
 
 /// VectorTargetTransformInfo - This interface is used by the vectorizers