#include "llvm/Transforms/Scalar.h"
#include "llvm/ADT/Statistic.h"
+#include "llvm/Analysis/GlobalsModRef.h"
#include "llvm/Analysis/InstructionSimplify.h"
#include "llvm/Analysis/LazyValueInfo.h"
#include "llvm/IR/CFG.h"
STATISTIC(NumSelects, "Number of selects propagated");
STATISTIC(NumMemAccess, "Number of memory access targets propagated");
STATISTIC(NumCmps, "Number of comparisons propagated");
+STATISTIC(NumReturns, "Number of return values propagated");
STATISTIC(NumDeadCases, "Number of switch cases removed");
namespace {
bool processMemAccess(Instruction *I);
bool processCmp(CmpInst *C);
bool processSwitch(SwitchInst *SI);
+ bool processCallSite(CallSite CS);
+
+ /// Return a constant value for V usable at At and everything it
+ /// dominates. If no such Constant can be found, return nullptr.
+ Constant *getConstantAt(Value *V, Instruction *At);
public:
static char ID;
void getAnalysisUsage(AnalysisUsage &AU) const override {
AU.addRequired<LazyValueInfo>();
+ AU.addPreserved<GlobalsAAWrapperPass>();
}
};
-} // namespace
+}
char CorrelatedValuePropagation::ID = 0;
INITIALIZE_PASS_BEGIN(CorrelatedValuePropagation, "correlated-propagation",
return true;
}
-/// processCmp - If the value of this comparison could be determined locally,
-/// constant propagation would already have figured it out. Instead, walk
-/// the predecessors and statically evaluate the comparison based on information
-/// available on that edge. If a given static evaluation is true on ALL
-/// incoming edges, then it's true universally and we can simplify the compare.
+/// processCmp - See if LazyValueInfo's ability to exploit edge conditions,
+/// or range information is sufficient to prove this comparison. Even for
+/// local conditions, this can sometimes prove conditions instcombine can't by
+/// exploiting range information.
bool CorrelatedValuePropagation::processCmp(CmpInst *C) {
Value *Op0 = C->getOperand(0);
- if (isa<Instruction>(Op0) &&
- cast<Instruction>(Op0)->getParent() == C->getParent())
- return false;
-
Constant *Op1 = dyn_cast<Constant>(C->getOperand(1));
if (!Op1) return false;
- pred_iterator PI = pred_begin(C->getParent()), PE = pred_end(C->getParent());
- if (PI == PE) return false;
+ // As a policy choice, we choose not to waste compile time on anything where
+ // the comparison is testing local values. While LVI can sometimes reason
+ // about such cases, it's not its primary purpose. We do make sure to do
+ // the block local query for uses from terminator instructions, but that's
+ // handled in the code for each terminator.
+ auto *I = dyn_cast<Instruction>(Op0);
+ if (I && I->getParent() == C->getParent())
+ return false;
- LazyValueInfo::Tristate Result = LVI->getPredicateOnEdge(C->getPredicate(),
- C->getOperand(0), Op1, *PI,
- C->getParent(), C);
+ LazyValueInfo::Tristate Result =
+ LVI->getPredicateAt(C->getPredicate(), Op0, Op1, C);
if (Result == LazyValueInfo::Unknown) return false;
- ++PI;
- while (PI != PE) {
- LazyValueInfo::Tristate Res = LVI->getPredicateOnEdge(C->getPredicate(),
- C->getOperand(0), Op1, *PI,
- C->getParent(), C);
- if (Res != Result) return false;
- ++PI;
- }
-
++NumCmps;
-
if (Result == LazyValueInfo::True)
C->replaceAllUsesWith(ConstantInt::getTrue(C->getContext()));
else
C->replaceAllUsesWith(ConstantInt::getFalse(C->getContext()));
-
C->eraseFromParent();
return true;
return Changed;
}
+/// processCallSite - Infer nonnull attributes for the arguments at the
+/// specified callsite.
+bool CorrelatedValuePropagation::processCallSite(CallSite CS) {
+ bool Changed = false;
+
+ unsigned ArgNo = 0;
+ for (Value *V : CS.args()) {
+ PointerType *Type = dyn_cast<PointerType>(V->getType());
+
+ if (Type && !CS.paramHasAttr(ArgNo + 1, Attribute::NonNull) &&
+ LVI->getPredicateAt(ICmpInst::ICMP_EQ, V,
+ ConstantPointerNull::get(Type),
+ CS.getInstruction()) == LazyValueInfo::False) {
+ AttributeSet AS = CS.getAttributes();
+ AS = AS.addAttribute(CS.getInstruction()->getContext(), ArgNo + 1,
+ Attribute::NonNull);
+ CS.setAttributes(AS);
+ Changed = true;
+ }
+ ArgNo++;
+ }
+ assert(ArgNo == CS.arg_size() && "sanity check");
+
+ return Changed;
+}
+
+Constant *CorrelatedValuePropagation::getConstantAt(Value *V, Instruction *At) {
+ if (Constant *C = LVI->getConstant(V, At->getParent(), At))
+ return C;
+
+ // TODO: The following really should be sunk inside LVI's core algorithm, or
+ // at least the outer shims around such.
+ auto *C = dyn_cast<CmpInst>(V);
+ if (!C) return nullptr;
+
+ Value *Op0 = C->getOperand(0);
+ Constant *Op1 = dyn_cast<Constant>(C->getOperand(1));
+ if (!Op1) return nullptr;
+
+ LazyValueInfo::Tristate Result =
+ LVI->getPredicateAt(C->getPredicate(), Op0, Op1, At);
+ if (Result == LazyValueInfo::Unknown)
+ return nullptr;
+
+ return (Result == LazyValueInfo::True) ?
+ ConstantInt::getTrue(C->getContext()) :
+ ConstantInt::getFalse(C->getContext());
+}
+
bool CorrelatedValuePropagation::runOnFunction(Function &F) {
if (skipOptnoneFunction(F))
return false;
for (Function::iterator FI = F.begin(), FE = F.end(); FI != FE; ++FI) {
bool BBChanged = false;
for (BasicBlock::iterator BI = FI->begin(), BE = FI->end(); BI != BE; ) {
- Instruction *II = BI++;
+ Instruction *II = &*BI++;
switch (II->getOpcode()) {
case Instruction::Select:
BBChanged |= processSelect(cast<SelectInst>(II));
case Instruction::Store:
BBChanged |= processMemAccess(II);
break;
+ case Instruction::Call:
+ case Instruction::Invoke:
+ BBChanged |= processCallSite(CallSite(II));
+ break;
}
}
case Instruction::Switch:
BBChanged |= processSwitch(cast<SwitchInst>(Term));
break;
+ case Instruction::Ret: {
+ auto *RI = cast<ReturnInst>(Term);
+ // Try to determine the return value if we can. This is mainly here to
+ // simplify the writing of unit tests, but also helps to enable IPO by
+ // constant folding the return values of callees.
+ auto *RetVal = RI->getReturnValue();
+ if (!RetVal) break; // handle "ret void"
+ if (isa<Constant>(RetVal)) break; // nothing to do
+ if (auto *C = getConstantAt(RetVal, RI)) {
+ ++NumReturns;
+ RI->replaceUsesOfWith(RetVal, C);
+ BBChanged = true;
+ }
}
+ };
FnChanged |= BBChanged;
}
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