[TRE] Improve code motion in TRE, use AA to tell whether a load can be moved before a call that writes to memory.
Summary: use AA to tell whether a load can be moved before a call that writes to memory.
Reviewers: dberlin, davide, sanjoy, hfinkel
Reviewed By: hfinkel
Subscribers: hfinkel, llvm-commits
Differential Revision: https://reviews.llvm.org/D34115
llvm-svn: 305698
diff --git a/llvm/lib/Transforms/Scalar/TailRecursionElimination.cpp b/llvm/lib/Transforms/Scalar/TailRecursionElimination.cpp
index 365566c..9397b87c 100644
--- a/llvm/lib/Transforms/Scalar/TailRecursionElimination.cpp
+++ b/llvm/lib/Transforms/Scalar/TailRecursionElimination.cpp
@@ -321,7 +321,7 @@
/// instruction from after the call to before the call, assuming that all
/// instructions between the call and this instruction are movable.
///
-static bool canMoveAboveCall(Instruction *I, CallInst *CI) {
+static bool canMoveAboveCall(Instruction *I, CallInst *CI, AliasAnalysis *AA) {
// FIXME: We can move load/store/call/free instructions above the call if the
// call does not mod/ref the memory location being processed.
if (I->mayHaveSideEffects()) // This also handles volatile loads.
@@ -332,10 +332,10 @@
if (CI->mayHaveSideEffects()) {
// Non-volatile loads may be moved above a call with side effects if it
// does not write to memory and the load provably won't trap.
- // FIXME: Writes to memory only matter if they may alias the pointer
+ // Writes to memory only matter if they may alias the pointer
// being loaded from.
const DataLayout &DL = L->getModule()->getDataLayout();
- if (CI->mayWriteToMemory() ||
+ if ((AA->getModRefInfo(CI, MemoryLocation::get(L)) & MRI_Mod) ||
!isSafeToLoadUnconditionally(L->getPointerOperand(),
L->getAlignment(), DL, L))
return false;
@@ -492,10 +492,11 @@
return CI;
}
-static bool
-eliminateRecursiveTailCall(CallInst *CI, ReturnInst *Ret, BasicBlock *&OldEntry,
- bool &TailCallsAreMarkedTail,
- SmallVectorImpl<PHINode *> &ArgumentPHIs) {
+static bool eliminateRecursiveTailCall(CallInst *CI, ReturnInst *Ret,
+ BasicBlock *&OldEntry,
+ bool &TailCallsAreMarkedTail,
+ SmallVectorImpl<PHINode *> &ArgumentPHIs,
+ AliasAnalysis *AA) {
// If we are introducing accumulator recursion to eliminate operations after
// the call instruction that are both associative and commutative, the initial
// value for the accumulator is placed in this variable. If this value is set
@@ -515,7 +516,8 @@
// Check that this is the case now.
BasicBlock::iterator BBI(CI);
for (++BBI; &*BBI != Ret; ++BBI) {
- if (canMoveAboveCall(&*BBI, CI)) continue;
+ if (canMoveAboveCall(&*BBI, CI, AA))
+ continue;
// If we can't move the instruction above the call, it might be because it
// is an associative and commutative operation that could be transformed
@@ -674,7 +676,8 @@
bool &TailCallsAreMarkedTail,
SmallVectorImpl<PHINode *> &ArgumentPHIs,
bool CannotTailCallElimCallsMarkedTail,
- const TargetTransformInfo *TTI) {
+ const TargetTransformInfo *TTI,
+ AliasAnalysis *AA) {
bool Change = false;
// Make sure this block is a trivial return block.
@@ -710,7 +713,7 @@
BB->eraseFromParent();
eliminateRecursiveTailCall(CI, RI, OldEntry, TailCallsAreMarkedTail,
- ArgumentPHIs);
+ ArgumentPHIs, AA);
++NumRetDuped;
Change = true;
}
@@ -723,16 +726,18 @@
bool &TailCallsAreMarkedTail,
SmallVectorImpl<PHINode *> &ArgumentPHIs,
bool CannotTailCallElimCallsMarkedTail,
- const TargetTransformInfo *TTI) {
+ const TargetTransformInfo *TTI,
+ AliasAnalysis *AA) {
CallInst *CI = findTRECandidate(Ret, CannotTailCallElimCallsMarkedTail, TTI);
if (!CI)
return false;
return eliminateRecursiveTailCall(CI, Ret, OldEntry, TailCallsAreMarkedTail,
- ArgumentPHIs);
+ ArgumentPHIs, AA);
}
-static bool eliminateTailRecursion(Function &F, const TargetTransformInfo *TTI) {
+static bool eliminateTailRecursion(Function &F, const TargetTransformInfo *TTI,
+ AliasAnalysis *AA) {
if (F.getFnAttribute("disable-tail-calls").getValueAsString() == "true")
return false;
@@ -767,11 +772,11 @@
if (ReturnInst *Ret = dyn_cast<ReturnInst>(BB->getTerminator())) {
bool Change =
processReturningBlock(Ret, OldEntry, TailCallsAreMarkedTail,
- ArgumentPHIs, !CanTRETailMarkedCall, TTI);
+ ArgumentPHIs, !CanTRETailMarkedCall, TTI, AA);
if (!Change && BB->getFirstNonPHIOrDbg() == Ret)
- Change =
- foldReturnAndProcessPred(BB, Ret, OldEntry, TailCallsAreMarkedTail,
- ArgumentPHIs, !CanTRETailMarkedCall, TTI);
+ Change = foldReturnAndProcessPred(BB, Ret, OldEntry,
+ TailCallsAreMarkedTail, ArgumentPHIs,
+ !CanTRETailMarkedCall, TTI, AA);
MadeChange |= Change;
}
}
@@ -801,6 +806,7 @@
void getAnalysisUsage(AnalysisUsage &AU) const override {
AU.addRequired<TargetTransformInfoWrapperPass>();
+ AU.addRequired<AAResultsWrapperPass>();
AU.addPreserved<GlobalsAAWrapperPass>();
}
@@ -809,7 +815,8 @@
return false;
return eliminateTailRecursion(
- F, &getAnalysis<TargetTransformInfoWrapperPass>().getTTI(F));
+ F, &getAnalysis<TargetTransformInfoWrapperPass>().getTTI(F),
+ &getAnalysis<AAResultsWrapperPass>().getAAResults());
}
};
}
@@ -830,8 +837,9 @@
FunctionAnalysisManager &AM) {
TargetTransformInfo &TTI = AM.getResult<TargetIRAnalysis>(F);
+ AliasAnalysis &AA = AM.getResult<AAManager>(F);
- bool Changed = eliminateTailRecursion(F, &TTI);
+ bool Changed = eliminateTailRecursion(F, &TTI, &AA);
if (!Changed)
return PreservedAnalyses::all();
diff --git a/llvm/test/Transforms/TailCallElim/reorder_load.ll b/llvm/test/Transforms/TailCallElim/reorder_load.ll
index 2f9b692..78621b1 100644
--- a/llvm/test/Transforms/TailCallElim/reorder_load.ll
+++ b/llvm/test/Transforms/TailCallElim/reorder_load.ll
@@ -7,6 +7,7 @@
; then eliminate the tail recursion.
+
@global = external global i32 ; <i32*> [#uses=1]
@extern_weak_global = extern_weak global i32 ; <i32*> [#uses=1]
@@ -145,3 +146,29 @@
%tmp10 = add i32 %tmp9, %tmp8 ; <i32> [#uses=1]
ret i32 %tmp10
}
+
+; This load can be moved above the call because the function call does not write to the memory the load
+; is accessing and the load is safe to speculate.
+define fastcc i32 @raise_load_6(i32* %a_arg, i32 %a_len_arg, i32 %start_arg) nounwind {
+; CHECK-LABEL: @raise_load_6(
+; CHECK-NOT: call
+; CHECK: load i32, i32*
+; CHECK-NOT: call
+; CHECK: }
+entry:
+ %s = alloca i32
+ store i32 4, i32* %s
+ %tmp2 = icmp sge i32 %start_arg, %a_len_arg ; <i1> [#uses=1]
+ br i1 %tmp2, label %if, label %else
+
+if: ; preds = %entry
+ store i32 1, i32* %a_arg
+ ret i32 0
+
+else: ; preds = %entry
+ %tmp7 = add i32 %start_arg, 1 ; <i32> [#uses=1]
+ %tmp8 = call fastcc i32 @raise_load_6(i32* %a_arg, i32 %a_len_arg, i32 %tmp7) ; <i32> [#uses=1]
+ %tmp9 = load i32, i32* %s ; <i32> [#uses=1]
+ %tmp10 = add i32 %tmp9, %tmp8 ; <i32> [#uses=1]
+ ret i32 %tmp10
+}