TargetLowering interface to set/get minimum block entries for jump tables.

Provide interface in TargetLowering to set or get the minimum number of basic
blocks whereby jump tables are generated for switch statements rather than an
if sequence.

    getMinimumJumpTableEntries() defaults to 4.
    setMinimumJumpTableEntries() allows target configuration.

    This patch changes the default for the Hexagon architecture to 5
    as it improves performance on some benchmarks.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@164628 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 15 insertions, 0 deletions

diff --git a/include/llvm/Target/TargetLowering.h b/include/llvm/Target/TargetLowering.h
index ff51048..9e46a40 100644
--- a/include/llvm/Target/TargetLowering.h
+++ b/include/llvm/Target/TargetLowering.h
@@ -712,6 +712,12 @@ public:
     return SupportJumpTables;
   }
 
+  /// getMinimumJumpTableEntries - return integer threshold on number of
+  /// blocks to use jump tables rather than if sequence.
+  int getMinimumJumpTableEntries() const {
+    return MinimumJumpTableEntries;
+  }
+
   /// getStackPointerRegisterToSaveRestore - If a physical register, this
   /// specifies the register that llvm.savestack/llvm.restorestack should save
   /// and restore.
@@ -1032,6 +1038,12 @@ protected:
     SupportJumpTables = Val;
   }
 
+  /// setMinimumJumpTableEntries - Indicate the number of blocks to generate
+  /// jump tables rather than if sequence.
+  void setMinimumJumpTableEntries(int Val) {
+    MinimumJumpTableEntries = Val;
+  }
+
   /// setStackPointerRegisterToSaveRestore - If set to a physical register, this
   /// specifies the register that llvm.savestack/llvm.restorestack should save
   /// and restore.
@@ -1826,6 +1838,9 @@ private:
   /// If it's not true, then each jumptable must be lowered into if-then-else's.
   bool SupportJumpTables;
 
+  /// MinimumJumpTableEntries - Number of blocks threshold to use jump tables.
+  int MinimumJumpTableEntries;
+
   /// BooleanContents - Information about the contents of the high-bits in
   /// boolean values held in a type wider than i1.  See getBooleanContents.
   BooleanContent BooleanContents;