caio/clang-p2996
1
0
Fork 0
Code Issues Pull Requests Actions Packages Projects Releases Wiki Activity

[SimplifyCFG] Common code sinking: relax restriction on non-uncond predecessors

Browse Source 
While we have a known profitability issue for sinking in presence of
non-unconditional predecessors, there isn't any known issues
for having multiple such non-unconditional predecessors,
so said restriction appears to be artificial. Lift it.
This commit is contained in:
Roman Lebedev
2021-04-28 22:47:15 +03:00
parent 410d03aabf
commit 1886aad9d0
2 changed files with 10 additions and 15 deletions
Download Patch File Download Diff File Expand all files Collapse all files

16
llvm/lib/Transforms/Utils/SimplifyCFG.cpp
View File

@@ -1988,15 +1988,13 @@ static bool SinkCommonCodeFromPredecessors(BasicBlock *BB,
// [ end ]
//
SmallVector<BasicBlock*,4> UnconditionalPreds;
Instruction *Cond = nullptr;
for (auto *B : predecessors(BB)) {
auto *T = B->getTerminator();
if (isa<BranchInst>(T) && cast<BranchInst>(T)->isUnconditional())
UnconditionalPreds.push_back(B);
else if ((isa<BranchInst>(T) || isa<SwitchInst>(T)) && !Cond)
Cond = T;
bool AllPredsAreUnconditional = false;
for (auto *PredBB : predecessors(BB)) {
auto *PredBr = dyn_cast<BranchInst>(PredBB->getTerminator());
if (PredBr && PredBr->isUnconditional())
UnconditionalPreds.push_back(PredBB);
else
return false;
AllPredsAreUnconditional = true;
}
if (UnconditionalPreds.size() < 2)
return false;
@@ -2063,7 +2061,7 @@ static bool SinkCommonCodeFromPredecessors(BasicBlock *BB,
bool Changed = false;
if (Cond) {
if (AllPredsAreUnconditional) {
// It is always legal to sink common instructions from unconditional
// predecessors. However, if not all predecessors are unconditional,
// this transformation might be pessimizing. So as a rule of thumb,

9
llvm/test/Transforms/SimplifyCFG/X86/sink-common-code.ll
View File

@@ -1538,14 +1538,11 @@ define void @multiple_cond_preds(i1 %c0, i1 %c1, i1 %c2) {
; CHECK-NEXT: br i1 [[C0:%.*]], label [[DISPATCH1:%.*]], label [[DISPATCH2:%.*]]
; CHECK: dispatch1:
; CHECK-NEXT: call void @direct_callee2()
; CHECK-NEXT: br i1 [[C1:%.*]], label [[UNCOND_PRED0:%.*]], label [[END:%.*]]
; CHECK-NEXT: br i1 [[C1:%.*]], label [[END_SINK_SPLIT:%.*]], label [[END:%.*]]
; CHECK: dispatch2:
; CHECK-NEXT: call void @direct_callee3()
; CHECK-NEXT: br i1 [[C2:%.*]], label [[UNCOND_PRED1:%.*]], label [[END]]
; CHECK: uncond_pred0:
; CHECK-NEXT: call void @direct_callee()
; CHECK-NEXT: br label [[END]]
; CHECK: uncond_pred1:
; CHECK-NEXT: br i1 [[C2:%.*]], label [[END_SINK_SPLIT]], label [[END]]
; CHECK: end.sink.split:
; CHECK-NEXT: call void @direct_callee()
; CHECK-NEXT: br label [[END]]
; CHECK: end: