[llvm-commits] [llvm] r120435 - in /llvm/trunk: include/llvm/Target/TargetLowering.h lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp lib/CodeGen/SelectionDAG/TargetLowering.cpp

[Chris Lattner]

Author: lattner
Date: Tue Nov 30 12:12:52 2010
New Revision: 120435

URL: http://llvm.org/viewvc/llvm-project?rev=120435&view=rev
Log:
add TLI support indicating that jumps are more expensive than logical operations
and use this to disable a specific optimization.  Patch by Micah Villmow!

Modified:
    llvm/trunk/include/llvm/Target/TargetLowering.h
    llvm/trunk/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
    llvm/trunk/lib/CodeGen/SelectionDAG/TargetLowering.cpp

Modified: llvm/trunk/include/llvm/Target/TargetLowering.h
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/include/llvm/Target/TargetLowering.h?rev=120435&r1=120434&r2=120435&view=diff
==============================================================================
--- llvm/trunk/include/llvm/Target/TargetLowering.h (original)
+++ llvm/trunk/include/llvm/Target/TargetLowering.h Tue Nov 30 12:12:52 2010
@@ -125,6 +125,10 @@
   /// srl/add/sra.
   bool isPow2DivCheap() const { return Pow2DivIsCheap; }
 
+  /// isJumpExpensive() - Return true if Flow Control is an expensive operation
+  /// that should be avoided.
+  bool isJumpExpensive() const { return JumpIsExpensive; }
+
   /// getSetCCResultType - Return the ValueType of the result of SETCC
   /// operations.  Also used to obtain the target's preferred type for
   /// the condition operand of SELECT and BRCOND nodes.  In the case of
@@ -1013,7 +1017,16 @@
 
   /// SelectIsExpensive - Tells the code generator not to expand operations
   /// into sequences that use the select operations if possible.
-  void setSelectIsExpensive() { SelectIsExpensive = true; }
+  void setSelectIsExpensive(bool isExpensive = true) { 
+    SelectIsExpensive = isExpensive; 
+  }
+
+  /// JumpIsExpensive - Tells the code generator not to expand sequence of 
+  /// operations into a seperate sequences that increases the amount of 
+  /// flow control.
+  void setJumpIsExpensive(bool isExpensive = true) {
+    JumpIsExpensive = isExpensive;
+  }
 
   /// setIntDivIsCheap - Tells the code generator that integer divide is
   /// expensive, and if possible, should be replaced by an alternate sequence
@@ -1597,6 +1610,11 @@
   /// it.
   bool Pow2DivIsCheap;
 
+  /// JumpIsExpensive - Tells the code generator that it shouldn't generate
+  /// extra flow control instructions and should attempt to combine flow
+  /// control instructions via predication.
+  bool JumpIsExpensive;
+
   /// UseUnderscoreSetJmp - This target prefers to use _setjmp to implement
   /// llvm.setjmp.  Defaults to false.
   bool UseUnderscoreSetJmp;

Modified: llvm/trunk/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp?rev=120435&r1=120434&r2=120435&view=diff
==============================================================================
--- llvm/trunk/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp (original)
+++ llvm/trunk/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp Tue Nov 30 12:12:52 2010
@@ -1403,6 +1403,7 @@
 
   // If this is a series of conditions that are or'd or and'd together, emit
   // this as a sequence of branches instead of setcc's with and/or operations.
+  // As long as jumps are not expensive, this should improve performance.
   // For example, instead of something like:
   //     cmp A, B
   //     C = seteq
@@ -1417,7 +1418,8 @@
   //     jle foo
   //
   if (const BinaryOperator *BOp = dyn_cast<BinaryOperator>(CondVal)) {
-    if (BOp->hasOneUse() &&
+    if (!TLI.isJumpExpensive() && 
+        BOp->hasOneUse() &&
         (BOp->getOpcode() == Instruction::And ||
          BOp->getOpcode() == Instruction::Or)) {
       FindMergedConditions(BOp, Succ0MBB, Succ1MBB, BrMBB, BrMBB,

Modified: llvm/trunk/lib/CodeGen/SelectionDAG/TargetLowering.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/CodeGen/SelectionDAG/TargetLowering.cpp?rev=120435&r1=120434&r2=120435&view=diff
==============================================================================
--- llvm/trunk/lib/CodeGen/SelectionDAG/TargetLowering.cpp (original)
+++ llvm/trunk/lib/CodeGen/SelectionDAG/TargetLowering.cpp Tue Nov 30 12:12:52 2010
@@ -572,6 +572,7 @@
   SelectIsExpensive = false;
   IntDivIsCheap = false;
   Pow2DivIsCheap = false;
+  JumpIsExpensive = false;
   StackPointerRegisterToSaveRestore = 0;
   ExceptionPointerRegister = 0;
   ExceptionSelectorRegister = 0;