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[JumpThread] Enhance finding partial redundant loads by continuing scanning single predecessor

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Summary: While scanning predecessors to find an available loaded value, if the predecessor has a single predecessor, we can continue scanning through the single predecessor.

Reviewers: mcrosier, rengolin, reames, davidxl, haicheng

Reviewed By: rengolin

Subscribers: zzheng, llvm-commits

Differential Revision: https://reviews.llvm.org/D29200

llvm-svn: 293896
This commit is contained in:
Jun Bum Lim 2017-02-02 15:12:34 +00:00
parent 417b2207b8
commit 296a001019
4 changed files with 105 additions and 6 deletions
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3
include/llvm/Analysis/Loads.h
View File

@ -85,7 +85,8 @@ Value *FindAvailableLoadedValue(LoadInst *Load,
BasicBlock::iterator &ScanFrom,
unsigned MaxInstsToScan = DefMaxInstsToScan,
AliasAnalysis *AA = nullptr,
bool *IsLoadCSE = nullptr);
bool *IsLoadCSE = nullptr,
unsigned *NumScanedInst = nullptr);
}

6
lib/Analysis/Loads.cpp
View File

@ -312,7 +312,8 @@ Value *llvm::FindAvailableLoadedValue(LoadInst *Load,
BasicBlock *ScanBB,
BasicBlock::iterator &ScanFrom,
unsigned MaxInstsToScan,
AliasAnalysis *AA, bool *IsLoadCSE) {
AliasAnalysis *AA, bool *IsLoadCSE,
unsigned *NumScanedInst) {
if (MaxInstsToScan == 0)
MaxInstsToScan = ~0U;
@ -344,6 +345,9 @@ Value *llvm::FindAvailableLoadedValue(LoadInst *Load,
// Restore ScanFrom to expected value in case next test succeeds
ScanFrom++;
if (NumScanedInst)
++(*NumScanedInst);
// Don't scan huge blocks.
if (MaxInstsToScan-- == 0)
return nullptr;

23
lib/Transforms/Scalar/JumpThreading.cpp
View File

@ -982,10 +982,25 @@ bool JumpThreadingPass::SimplifyPartiallyRedundantLoad(LoadInst *LI) {
// Scan the predecessor to see if the value is available in the pred.
BBIt = PredBB->end();
Value *PredAvailable = FindAvailableLoadedValue(LI, PredBB, BBIt,
DefMaxInstsToScan,
nullptr,
&IsLoadCSE);
unsigned NumScanedInst = 0;
Value *PredAvailable =
FindAvailableLoadedValue(LI, PredBB, BBIt, DefMaxInstsToScan, nullptr,
&IsLoadCSE, &NumScanedInst);
// If PredBB has a single predecessor, continue scanning through the single
// precessor.
BasicBlock *SinglePredBB = PredBB;
while (!PredAvailable && SinglePredBB && BBIt == SinglePredBB->begin() &&
NumScanedInst < DefMaxInstsToScan) {
SinglePredBB = SinglePredBB->getSinglePredecessor();
if (SinglePredBB) {
BBIt = SinglePredBB->end();
PredAvailable = FindAvailableLoadedValue(
LI, SinglePredBB, BBIt, (DefMaxInstsToScan - NumScanedInst),
nullptr, &IsLoadCSE, &NumScanedInst);
}
}
if (!PredAvailable) {
OneUnavailablePred = PredBB;
continue;

79
test/Transforms/JumpThreading/thread-loads.ll
View File

@ -302,6 +302,85 @@ ret2:
ret void
}
define i32 @fn_SinglePred(i1 %c2,i64* %P) {
; CHECK-LABEL: @fn_SinglePred
; CHECK-LABEL: entry:
; CHECK: %[[L1:.*]] = load i64, i64* %P
; CHECK: br i1 %c, label %cond3, label %cond1
; CHECK-LABEL: cond2:
; CHECK-NOT: load
; CHECK: %[[PHI:.*]] = phi i64 [ %[[L1]], %cond1 ]
; CHECK: call void @fn2(i64 %[[PHI]])
; CHECK: br label %end
; CHECK-LABEL: cond3:
; CHECK: call void @fn2(i64 %l1)
; CHECK: call void @fn3(i64 %l1)
entry:
%l1 = load i64, i64* %P
%c = icmp eq i64 %l1, 0
br i1 %c, label %cond2, label %cond1
cond1:
br i1 %c2, label %cond2, label %end
cond2:
%l2 = load i64, i64* %P
call void @fn2(i64 %l2)
%c3 = icmp eq i64 %l2, 0
br i1 %c3, label %cond3, label %end
cond3:
call void @fn3(i64 %l2)
br label %end
end:
ret i32 0
}
define i32 @fn_SinglePredMultihop(i1 %c1, i1 %c2,i64* %P) {
; CHECK-LABEL: @fn_SinglePredMultihop
; CHECK-LABEL: entry:
; CHECK: %[[L1:.*]] = load i64, i64* %P
; CHECK: br i1 %c0, label %cond3, label %cond0
; CHECK-LABEL: cond2:
; CHECK-NOT: load
; CHECK: %[[PHI:.*]] = phi i64 [ %[[L1]], %cond1 ]
; CHECK: call void @fn2(i64 %[[PHI]])
; CHECK: br label %end
; CHECK-LABEL: cond3:
; CHECK: call void @fn2(i64 %l1)
; CHECK: call void @fn3(i64 %l1)
entry:
%l1 = load i64, i64* %P
%c0 = icmp eq i64 %l1, 0
br i1 %c0, label %cond2, label %cond0
cond0:
br i1 %c1, label %cond1, label %end
cond1:
br i1 %c2, label %cond2, label %end
cond2:
%l2 = load i64, i64* %P
call void @fn2(i64 %l2)
%c3 = icmp eq i64 %l2, 0
br i1 %c3, label %cond3, label %end
cond3:
call void @fn3(i64 %l2)
br label %end
end:
ret i32 0
}
declare void @fn2(i64)
declare void @fn3(i64)
!0 = !{!3, !3, i64 0}
!1 = !{!"omnipotent char", !2}
!2 = !{!"Simple C/C++ TBAA"}