add TLI support indicating that jumps are more expensive than logical operations
and use this to disable a specific optimization. Patch by Micah Villmow!
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@120435 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/include/llvm/Target/TargetLowering.h b/include/llvm/Target/TargetLowering.h
index 75e5325..b450f42 100644
--- a/include/llvm/Target/TargetLowering.h
+++ b/include/llvm/Target/TargetLowering.h
@@ -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;
diff --git a/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp b/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
index d00643f..6dfc6b5 100644
--- a/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
+++ b/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
@@ -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,
diff --git a/lib/CodeGen/SelectionDAG/TargetLowering.cpp b/lib/CodeGen/SelectionDAG/TargetLowering.cpp
index 12ca9291..b2c2dbb 100644
--- a/lib/CodeGen/SelectionDAG/TargetLowering.cpp
+++ b/lib/CodeGen/SelectionDAG/TargetLowering.cpp
@@ -572,6 +572,7 @@
SelectIsExpensive = false;
IntDivIsCheap = false;
Pow2DivIsCheap = false;
+ JumpIsExpensive = false;
StackPointerRegisterToSaveRestore = 0;
ExceptionPointerRegister = 0;
ExceptionSelectorRegister = 0;