Do not speculatively execute an instruction by hoisting it to its predecessor BB if any of its operands are defined but not used in BB. The transformation will prevent the operand from being sunk into the use block.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@52244 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Transforms/Utils/SimplifyCFG.cpp b/lib/Transforms/Utils/SimplifyCFG.cpp
index 605855d..a993784 100644
--- a/lib/Transforms/Utils/SimplifyCFG.cpp
+++ b/lib/Transforms/Utils/SimplifyCFG.cpp
@@ -23,12 +23,15 @@
#include "llvm/Transforms/Utils/BasicBlockUtils.h"
#include "llvm/ADT/SmallVector.h"
#include "llvm/ADT/SmallPtrSet.h"
+#include "llvm/ADT/Statistic.h"
#include <algorithm>
#include <functional>
#include <set>
#include <map>
using namespace llvm;
+STATISTIC(NumSpeculations, "Number of speculative executed instructions");
+
/// SafeToMergeTerminators - Return true if it is safe to merge these two
/// terminator instructions together.
///
@@ -1030,12 +1033,22 @@
if (!FalseV) // Can this happen?
return false;
+ // Do not hoist the instruction if any of its operands are defined but not
+ // used in this BB. The transformation will prevent the operand from
+ // being sunk into the use block.
+ for (User::op_iterator i = I->op_begin(), e = I->op_end(); i != e; ++i) {
+ Instruction *OpI = dyn_cast<Instruction>(*i);
+ if (OpI && OpI->getParent() == BIParent &&
+ !OpI->isUsedInBasicBlock(BIParent))
+ return false;
+ }
+
// If we get here, we can hoist the instruction. Try to place it before the
- // icmp / fcmp instruction preceeding the conditional branch.
+ // icmp instruction preceeding the conditional branch.
BasicBlock::iterator InsertPos = BI;
if (InsertPos != BIParent->begin())
--InsertPos;
- if (InsertPos == BrCond)
+ if (InsertPos == BrCond && !isa<PHINode>(BrCond))
BIParent->getInstList().splice(InsertPos, BB1->getInstList(), I);
else
BIParent->getInstList().splice(BI, BB1->getInstList(), I);
@@ -1060,6 +1073,7 @@
PN->setIncomingValue(j, SI);
}
+ ++NumSpeculations;
return true;
}