commit 1408e7e17525287c596a8f575957aecb684fa75d
author shkzhang <shkzhang@cn.ibm.com> Wed Dec 11 04:46:00 2019 -0500
committer shkzhang <shkzhang@cn.ibm.com> Wed Dec 11 04:46:00 2019 -0500
tree 9dbf83122387cd937f9ece7a4383d8139a1847a2
parent 11f311875f092e59cac2936b54f922b968e615e3

[PowerPC] [CodeGen] Use MachineBranchProbabilityInfo in EarlyIfPredicator to avoid the potential bug

Summary:
In the function `EarlyIfPredicator::shouldConvertIf()`, we call
`TII->isProfitableToIfCvt()` with `BranchProbability::getUnknown()`, it may
cause the potential assertion error for those hook which use `BranchProbability`
in `isProfitableToIfCvt()`, for example `SystemZ`.
`SystemZ` use `Probability < BranchProbability(1, 8))` in the function
`SystemZInstrInfo::isProfitableToIfCvt()`, if we call this function with
`BranchProbability::getUnknown()`, it will cause assertion error.

This patch is to fix the potential bug.

Reviewed By: ThomasRaoux

Differential Revision: https://reviews.llvm.org/D71273

llvm/lib/CodeGen/EarlyIfConversion.cpp

diff --git a/llvm/lib/CodeGen/EarlyIfConversion.cpp b/llvm/lib/CodeGen/EarlyIfConversion.cpp
index 92bd9d1..d45e424 100644
--- a/llvm/lib/CodeGen/EarlyIfConversion.cpp
+++ b/llvm/lib/CodeGen/EarlyIfConversion.cpp
@@ -941,6 +941,7 @@
   TargetSchedModel SchedModel;
   MachineRegisterInfo *MRI;
   MachineDominatorTree *DomTree;
+  MachineBranchProbabilityInfo *MBPI;
   MachineLoopInfo *Loops;
   SSAIfConv IfConv;
 
@@ -966,10 +967,12 @@
 INITIALIZE_PASS_BEGIN(EarlyIfPredicator, DEBUG_TYPE, "Early If Predicator",
                       false, false)
 INITIALIZE_PASS_DEPENDENCY(MachineDominatorTree)
+INITIALIZE_PASS_DEPENDENCY(MachineBranchProbabilityInfo)
 INITIALIZE_PASS_END(EarlyIfPredicator, DEBUG_TYPE, "Early If Predicator", false,
                     false)
 
 void EarlyIfPredicator::getAnalysisUsage(AnalysisUsage &AU) const {
+  AU.addRequired<MachineBranchProbabilityInfo>();
   AU.addRequired<MachineDominatorTree>();
   AU.addPreserved<MachineDominatorTree>();
   AU.addRequired<MachineLoopInfo>();
@@ -979,6 +982,7 @@
 
 /// Apply the target heuristic to decide if the transformation is profitable.
 bool EarlyIfPredicator::shouldConvertIf() {
+  auto TrueProbability = MBPI->getEdgeProbability(IfConv.Head, IfConv.TBB);
   if (IfConv.isTriangle()) {
     MachineBasicBlock &IfBlock =
         (IfConv.TBB == IfConv.Tail) ? *IfConv.FBB : *IfConv.TBB;
@@ -993,7 +997,7 @@
     }
 
     return TII->isProfitableToIfCvt(IfBlock, Cycles, ExtraPredCost,
-                                    BranchProbability::getUnknown());
+                                    TrueProbability);
   }
   unsigned TExtra = 0;
   unsigned FExtra = 0;
@@ -1012,8 +1016,7 @@
     FExtra += TII->getPredicationCost(I);
   }
   return TII->isProfitableToIfCvt(*IfConv.TBB, TCycle, TExtra, *IfConv.FBB,
-                                  FCycle, FExtra,
-                                  BranchProbability::getUnknown());
+                                  FCycle, FExtra, TrueProbability);
 }
 
 /// Attempt repeated if-conversion on MBB, return true if successful.
@@ -1044,6 +1047,7 @@
   SchedModel.init(&STI);
   DomTree = &getAnalysis<MachineDominatorTree>();
   Loops = getAnalysisIfAvailable<MachineLoopInfo>();
+  MBPI = &getAnalysis<MachineBranchProbabilityInfo>();
 
   bool Changed = false;
   IfConv.runOnMachineFunction(MF);