[llvm-branch-commits] [llvm-branch] r329793 - Backport of rL326666 and rL326668 for PR36607 and PR36608.
Florian Hahn via llvm-branch-commits
llvm-branch-commits at lists.llvm.org
Wed Apr 11 05:01:38 PDT 2018
Author: fhahn
Date: Wed Apr 11 05:01:38 2018
New Revision: 329793
URL: http://llvm.org/viewvc/llvm-project?rev=329793&view=rev
Log:
Backport of rL326666 and rL326668 for PR36607 and PR36608.
[CallSiteSplitting] properly split musttail calls.
The original author was Fedor Indutny <fedor at indutny.com>.
`musttail` calls can't be naively splitted. The split blocks must
include not only the call instruction itself, but also (optional)
`bitcast` and `return` instructions that follow it.
Clone `bitcast` and `ret`, place them into the split blocks, and
remove the tail block when done.
Reviewers: junbuml, mcrosier, davidxl, davide, fhahn
Reviewed By: fhahn
Subscribers: JDevlieghere, llvm-commits
Differential Revision: https://reviews.llvm.org/D43729
Added:
llvm/branches/release_60/test/Transforms/CallSiteSplitting/musttail.ll
Modified:
llvm/branches/release_60/lib/Transforms/Scalar/CallSiteSplitting.cpp
Modified: llvm/branches/release_60/lib/Transforms/Scalar/CallSiteSplitting.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/branches/release_60/lib/Transforms/Scalar/CallSiteSplitting.cpp?rev=329793&r1=329792&r2=329793&view=diff
==============================================================================
--- llvm/branches/release_60/lib/Transforms/Scalar/CallSiteSplitting.cpp (original)
+++ llvm/branches/release_60/lib/Transforms/Scalar/CallSiteSplitting.cpp Wed Apr 11 05:01:38 2018
@@ -201,6 +201,46 @@ static bool canSplitCallSite(CallSite CS
return CallSiteBB->canSplitPredecessors();
}
+static Instruction *cloneInstForMustTail(Instruction *I, Instruction *Before,
+ Value *V) {
+ Instruction *Copy = I->clone();
+ Copy->setName(I->getName());
+ Copy->insertBefore(Before);
+ if (V)
+ Copy->setOperand(0, V);
+ return Copy;
+}
+
+/// Copy mandatory `musttail` return sequence that follows original `CI`, and
+/// link it up to `NewCI` value instead:
+///
+/// * (optional) `bitcast NewCI to ...`
+/// * `ret bitcast or NewCI`
+///
+/// Insert this sequence right before `SplitBB`'s terminator, which will be
+/// cleaned up later in `splitCallSite` below.
+static void copyMustTailReturn(BasicBlock *SplitBB, Instruction *CI,
+ Instruction *NewCI) {
+ bool IsVoid = SplitBB->getParent()->getReturnType()->isVoidTy();
+ auto II = std::next(CI->getIterator());
+
+ BitCastInst *BCI = dyn_cast<BitCastInst>(&*II);
+ if (BCI)
+ ++II;
+
+ ReturnInst *RI = dyn_cast<ReturnInst>(&*II);
+ assert(RI && "`musttail` call must be followed by `ret` instruction");
+
+ TerminatorInst *TI = SplitBB->getTerminator();
+ Value *V = NewCI;
+ if (BCI)
+ V = cloneInstForMustTail(BCI, TI, V);
+ cloneInstForMustTail(RI, TI, IsVoid ? nullptr : V);
+
+ // FIXME: remove TI here, `DuplicateInstructionsInSplitBetween` has a bug
+ // that prevents doing this now.
+}
+
/// Return true if the CS is split into its new predecessors which are directly
/// hooked to each of its original predecessors pointed by PredBB1 and PredBB2.
/// CallInst1 and CallInst2 will be the new call-sites placed in the new
@@ -245,6 +285,7 @@ static void splitCallSite(CallSite CS, B
Instruction *CallInst1, Instruction *CallInst2) {
Instruction *Instr = CS.getInstruction();
BasicBlock *TailBB = Instr->getParent();
+ bool IsMustTailCall = CS.isMustTailCall();
assert(Instr == (TailBB->getFirstNonPHIOrDbg()) && "Unexpected call-site");
BasicBlock *SplitBlock1 =
@@ -276,9 +317,14 @@ static void splitCallSite(CallSite CS, B
++ArgNo;
}
}
+ // Clone and place bitcast and return instructions before `TI`
+ if (IsMustTailCall) {
+ copyMustTailReturn(SplitBlock1, CS.getInstruction(), CallInst1);
+ copyMustTailReturn(SplitBlock2, CS.getInstruction(), CallInst2);
+ }
// Replace users of the original call with a PHI mering call-sites split.
- if (Instr->getNumUses()) {
+ if (!IsMustTailCall && Instr->getNumUses()) {
PHINode *PN = PHINode::Create(Instr->getType(), 2, "phi.call",
TailBB->getFirstNonPHI());
PN->addIncoming(CallInst1, SplitBlock1);
@@ -290,8 +336,25 @@ static void splitCallSite(CallSite CS, B
<< "\n");
DEBUG(dbgs() << " " << *CallInst2 << " in " << SplitBlock2->getName()
<< "\n");
- Instr->eraseFromParent();
+
NumCallSiteSplit++;
+
+ // FIXME: remove TI in `copyMustTailReturn`
+ if (IsMustTailCall) {
+ // Remove superfluous `br` terminators from the end of the Split blocks
+ // NOTE: Removing terminator removes the SplitBlock from the TailBB's
+ // predecessors. Therefore we must get complete list of Splits before
+ // attempting removal.
+ SmallVector<BasicBlock *, 2> Splits(predecessors((TailBB)));
+ assert(Splits.size() == 2 && "Expected exactly 2 splits!");
+ for (unsigned i = 0; i < Splits.size(); i++)
+ Splits[i]->getTerminator()->eraseFromParent();
+
+ // Erase the tail block once done with musttail patching
+ TailBB->eraseFromParent();
+ return;
+ }
+ Instr->eraseFromParent();
}
// Return true if the call-site has an argument which is a PHI with only
@@ -369,7 +432,17 @@ static bool doCallSiteSplitting(Function
Function *Callee = CS.getCalledFunction();
if (!Callee || Callee->isDeclaration())
continue;
+
+ // Successful musttail call-site splits result in erased CI and erased BB.
+ // Check if such path is possible before attempting the splitting.
+ bool IsMustTail = CS.isMustTailCall();
+
Changed |= tryToSplitCallSite(CS);
+
+ // There're no interesting instructions after this. The call site
+ // itself might have been erased on splitting.
+ if (IsMustTail)
+ break;
}
}
return Changed;
Added: llvm/branches/release_60/test/Transforms/CallSiteSplitting/musttail.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/branches/release_60/test/Transforms/CallSiteSplitting/musttail.ll?rev=329793&view=auto
==============================================================================
--- llvm/branches/release_60/test/Transforms/CallSiteSplitting/musttail.ll (added)
+++ llvm/branches/release_60/test/Transforms/CallSiteSplitting/musttail.ll Wed Apr 11 05:01:38 2018
@@ -0,0 +1,109 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
+; RUN: opt < %s -callsite-splitting -S | FileCheck %s
+
+define i8* @caller(i8* %a, i8* %b) {
+; CHECK-LABEL: @caller(
+; CHECK-NEXT: Top:
+; CHECK-NEXT: [[C:%.*]] = icmp eq i8* [[A:%.*]], null
+; CHECK-NEXT: br i1 [[C]], label [[TAIL_PREDBB1_SPLIT:%.*]], label [[TBB:%.*]]
+; CHECK: TBB:
+; CHECK-NEXT: [[C2:%.*]] = icmp eq i8* [[B:%.*]], null
+; CHECK-NEXT: br i1 [[C2]], label [[TAIL_PREDBB2_SPLIT:%.*]], label [[END:%.*]]
+; CHECK: Tail.predBB1.split:
+; CHECK-NEXT: [[TMP0:%.*]] = musttail call i8* @callee(i8* null, i8* [[B]])
+; CHECK-NEXT: [[CB1:%.*]] = bitcast i8* [[TMP0]] to i8*
+; CHECK-NEXT: ret i8* [[CB1]]
+; CHECK: Tail.predBB2.split:
+; CHECK-NEXT: [[TMP1:%.*]] = musttail call i8* @callee(i8* nonnull [[A]], i8* null)
+; CHECK-NEXT: [[CB2:%.*]] = bitcast i8* [[TMP1]] to i8*
+; CHECK-NEXT: ret i8* [[CB2]]
+; CHECK: End:
+; CHECK-NEXT: ret i8* null
+;
+Top:
+ %c = icmp eq i8* %a, null
+ br i1 %c, label %Tail, label %TBB
+TBB:
+ %c2 = icmp eq i8* %b, null
+ br i1 %c2, label %Tail, label %End
+Tail:
+ %ca = musttail call i8* @callee(i8* %a, i8* %b)
+ %cb = bitcast i8* %ca to i8*
+ ret i8* %cb
+End:
+ ret i8* null
+}
+
+define i8* @callee(i8* %a, i8* %b) noinline {
+; CHECK-LABEL: define i8* @callee(
+; CHECK-NEXT: ret i8* [[A:%.*]]
+;
+ ret i8* %a
+}
+
+define i8* @no_cast_caller(i8* %a, i8* %b) {
+; CHECK-LABEL: @no_cast_caller(
+; CHECK-NEXT: Top:
+; CHECK-NEXT: [[C:%.*]] = icmp eq i8* [[A:%.*]], null
+; CHECK-NEXT: br i1 [[C]], label [[TAIL_PREDBB1_SPLIT:%.*]], label [[TBB:%.*]]
+; CHECK: TBB:
+; CHECK-NEXT: [[C2:%.*]] = icmp eq i8* [[B:%.*]], null
+; CHECK-NEXT: br i1 [[C2]], label [[TAIL_PREDBB2_SPLIT:%.*]], label [[END:%.*]]
+; CHECK: Tail.predBB1.split:
+; CHECK-NEXT: [[TMP0:%.*]] = musttail call i8* @callee(i8* null, i8* [[B]])
+; CHECK-NEXT: ret i8* [[TMP0]]
+; CHECK: Tail.predBB2.split:
+; CHECK-NEXT: [[TMP1:%.*]] = musttail call i8* @callee(i8* nonnull [[A]], i8* null)
+; CHECK-NEXT: ret i8* [[TMP1]]
+; CHECK: End:
+; CHECK-NEXT: ret i8* null
+;
+Top:
+ %c = icmp eq i8* %a, null
+ br i1 %c, label %Tail, label %TBB
+TBB:
+ %c2 = icmp eq i8* %b, null
+ br i1 %c2, label %Tail, label %End
+Tail:
+ %ca = musttail call i8* @callee(i8* %a, i8* %b)
+ ret i8* %ca
+End:
+ ret i8* null
+}
+
+define void @void_caller(i8* %a, i8* %b) {
+; CHECK-LABEL: @void_caller(
+; CHECK-NEXT: Top:
+; CHECK-NEXT: [[C:%.*]] = icmp eq i8* [[A:%.*]], null
+; CHECK-NEXT: br i1 [[C]], label [[TAIL_PREDBB1_SPLIT:%.*]], label [[TBB:%.*]]
+; CHECK: TBB:
+; CHECK-NEXT: [[C2:%.*]] = icmp eq i8* [[B:%.*]], null
+; CHECK-NEXT: br i1 [[C2]], label [[TAIL_PREDBB2_SPLIT:%.*]], label [[END:%.*]]
+; CHECK: Tail.predBB1.split:
+; CHECK-NEXT: musttail call void @void_callee(i8* null, i8* [[B]])
+; CHECK-NEXT: ret void
+; CHECK: Tail.predBB2.split:
+; CHECK-NEXT: musttail call void @void_callee(i8* nonnull [[A]], i8* null)
+; CHECK-NEXT: ret void
+; CHECK: End:
+; CHECK-NEXT: ret void
+;
+Top:
+ %c = icmp eq i8* %a, null
+ br i1 %c, label %Tail, label %TBB
+TBB:
+ %c2 = icmp eq i8* %b, null
+ br i1 %c2, label %Tail, label %End
+Tail:
+ musttail call void @void_callee(i8* %a, i8* %b)
+ ret void
+End:
+ ret void
+}
+
+define void @void_callee(i8* %a, i8* %b) noinline {
+; CHECK-LABEL: define void @void_callee(
+; CHECK-NEXT: ret void
+;
+ ret void
+}
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