[llvm-commits] [llvm] r136583 - /llvm/trunk/lib/Analysis/BranchProbabilityInfo.cpp
Jakub Staszak
jstaszak at apple.com
Sat Jul 30 20:27:24 PDT 2011
Author: kuba
Date: Sat Jul 30 22:27:24 2011
New Revision: 136583
URL: http://llvm.org/viewvc/llvm-project?rev=136583&view=rev
Log:
Add Zero Heurestics to BranchProbabilityInfo. If we compare value to zero we
decide whether condition is likely to be true this way:
x == 0 -> false
x < 0 -> false
x <= 0 -> false
x != 0 -> true
x > 0 -> true
x >= 0 -> true
Modified:
llvm/trunk/lib/Analysis/BranchProbabilityInfo.cpp
Modified: llvm/trunk/lib/Analysis/BranchProbabilityInfo.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Analysis/BranchProbabilityInfo.cpp?rev=136583&r1=136582&r2=136583&view=diff
==============================================================================
--- llvm/trunk/lib/Analysis/BranchProbabilityInfo.cpp (original)
+++ llvm/trunk/lib/Analysis/BranchProbabilityInfo.cpp Sat Jul 30 22:27:24 2011
@@ -11,6 +11,7 @@
//
//===----------------------------------------------------------------------===//
+#include "llvm/Constants.h"
#include "llvm/Instructions.h"
#include "llvm/Analysis/BranchProbabilityInfo.h"
#include "llvm/Analysis/LoopInfo.h"
@@ -72,6 +73,9 @@
static const uint32_t PH_TAKEN_WEIGHT = 20;
static const uint32_t PH_NONTAKEN_WEIGHT = 12;
+ static const uint32_t ZH_TAKEN_WEIGHT = 20;
+ static const uint32_t ZH_NONTAKEN_WEIGHT = 12;
+
// Standard weight value. Used when none of the heuristics set weight for
// the edge.
static const uint32_t NORMAL_WEIGHT = 16;
@@ -125,6 +129,9 @@
// Loop Branch Heuristics
bool calcLoopBranchHeuristics(BasicBlock *BB);
+ // Zero Heurestics
+ bool calcZeroHeuristics(BasicBlock *BB);
+
bool runOnFunction(Function &F);
};
} // end anonymous namespace
@@ -270,6 +277,86 @@
return true;
}
+bool BranchProbabilityAnalysis::calcZeroHeuristics(BasicBlock *BB) {
+ BranchInst * BI = dyn_cast<BranchInst>(BB->getTerminator());
+ if (!BI || !BI->isConditional())
+ return false;
+
+ Value *Cond = BI->getCondition();
+ ICmpInst *CI = dyn_cast<ICmpInst>(Cond);
+ if (!CI)
+ return false;
+
+ Value *LHS = CI->getOperand(0);
+ Value *RHS = CI->getOperand(1);
+
+ bool hasZero = false;
+ bool lhsZero = false;
+ if (ConstantInt *CI = dyn_cast<ConstantInt>(LHS)) {
+ hasZero = CI->isZero();
+ lhsZero = true;
+ }
+
+ if (!hasZero)
+ if (ConstantInt *CI = dyn_cast<ConstantInt>(RHS))
+ hasZero = CI->isZero();
+
+ if (!hasZero)
+ return false;
+
+ bool isProb;
+ switch (CI->getPredicate()) {
+ case CmpInst::ICMP_EQ:
+ // Equal to zero is not expected to be taken.
+ isProb = false;
+ break;
+
+ case CmpInst::ICMP_NE:
+ // Not equal to zero is expected.
+ isProb = true;
+ break;
+
+ case CmpInst::ICMP_ULT:
+ case CmpInst::ICMP_ULE:
+ case CmpInst::ICMP_SLT:
+ case CmpInst::ICMP_SLE:
+ // Less or equal to zero is not expected.
+ // 0 < X -> isProb = true
+ // 0 <= X -> isProb = true
+ // X < 0 -> isProb = false
+ // X <= 0 -> isProb = false
+ isProb = lhsZero;
+ break;
+
+ case CmpInst::ICMP_UGT:
+ case CmpInst::ICMP_UGE:
+ case CmpInst::ICMP_SGT:
+ case CmpInst::ICMP_SGE:
+ // Greater or equal to zero is expected.
+ // 0 > X -> isProb = false
+ // 0 >= X -> isProb = false
+ // X > 0 -> isProb = true
+ // X >= 0 -> isProb = true
+ isProb = !lhsZero;
+ break;
+
+ default:
+ return false;
+ };
+
+ BasicBlock *Taken = BI->getSuccessor(0);
+ BasicBlock *NonTaken = BI->getSuccessor(1);
+
+ if (!isProb)
+ std::swap(Taken, NonTaken);
+
+ BP->setEdgeWeight(BB, Taken, ZH_TAKEN_WEIGHT);
+ BP->setEdgeWeight(BB, NonTaken, ZH_NONTAKEN_WEIGHT);
+
+ return true;
+}
+
+
bool BranchProbabilityAnalysis::runOnFunction(Function &F) {
for (Function::iterator I = F.begin(), E = F.end(); I != E; ) {
@@ -284,7 +371,10 @@
if (calcReturnHeuristics(BB))
continue;
- calcPointerHeuristics(BB);
+ if (calcPointerHeuristics(BB))
+ continue;
+
+ calcZeroHeuristics(BB);
}
return false;
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