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[CVP] Improve the value solving of select at use #76700

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Jan 5, 2024
Merged

[CVP] Improve the value solving of select at use #76700

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40f29d2
[CVP] Add pre-commit tests. NFC.
dtcxzyw Jan 2, 2024
3c315b1
[CVP] Solve value of select at use
dtcxzyw Jan 2, 2024
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51 changes: 26 additions & 25 deletions llvm/lib/Transforms/Scalar/CorrelatedValuePropagation.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -94,6 +94,31 @@ STATISTIC(NumUDivURemsNarrowedExpanded,
"Number of bound udiv's/urem's expanded");
STATISTIC(NumZExt, "Number of non-negative deductions");

static Constant *getConstantAt(Value *V, Instruction *At, LazyValueInfo *LVI) {
if (Constant *C = LVI->getConstant(V, 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, /*UseBlockValue=*/false);
if (Result == LazyValueInfo::Unknown)
return nullptr;

return (Result == LazyValueInfo::True)
? ConstantInt::getTrue(C->getContext())
: ConstantInt::getFalse(C->getContext());
}

static bool processSelect(SelectInst *S, LazyValueInfo *LVI) {
if (S->getType()->isVectorTy() || isa<Constant>(S->getCondition()))
return false;
Expand All @@ -106,7 +131,7 @@ static bool processSelect(SelectInst *S, LazyValueInfo *LVI) {
C = LVI->getConstantOnEdge(S->getCondition(), PN->getIncomingBlock(U),
I->getParent(), I);
else
C = LVI->getConstant(S->getCondition(), I);
C = getConstantAt(S->getCondition(), I, LVI);

auto *CI = dyn_cast_or_null<ConstantInt>(C);
if (!CI)
Expand Down Expand Up @@ -1109,30 +1134,6 @@ static bool processAnd(BinaryOperator *BinOp, LazyValueInfo *LVI) {
return true;
}


static Constant *getConstantAt(Value *V, Instruction *At, LazyValueInfo *LVI) {
if (Constant *C = LVI->getConstant(V, 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, /*UseBlockValue=*/false);
if (Result == LazyValueInfo::Unknown)
return nullptr;

return (Result == LazyValueInfo::True) ?
ConstantInt::getTrue(C->getContext()) :
ConstantInt::getFalse(C->getContext());
}

static bool runImpl(Function &F, LazyValueInfo *LVI, DominatorTree *DT,
const SimplifyQuery &SQ) {
bool FnChanged = false;
Expand Down
23 changes: 23 additions & 0 deletions llvm/test/Transforms/CorrelatedValuePropagation/select.ll
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Original file line number Diff line number Diff line change
Expand Up @@ -372,4 +372,27 @@ define i64 @select_cond_may_undef(i32 %a) {
ret i64 %max
}

define i32 @test_solve_select_at_use(i32 %a, i32 %b, i32 %c) {
; CHECK-LABEL: define i32 @test_solve_select_at_use
; CHECK-SAME: (i32 [[A:%.*]], i32 [[B:%.*]], i32 [[C:%.*]]) {
; CHECK-NEXT: entry:
; CHECK-NEXT: [[CMP:%.*]] = icmp slt i32 [[A]], 0
; CHECK-NEXT: [[COND:%.*]] = icmp sgt i32 [[A]], -1
; CHECK-NEXT: br i1 [[COND]], label [[IF_THEN:%.*]], label [[IF_ELSE:%.*]]
; CHECK: if.then:
; CHECK-NEXT: ret i32 [[C]]
; CHECK: if.else:
; CHECK-NEXT: ret i32 [[B]]
;
entry:
%cmp = icmp slt i32 %a, 0
%retval = select i1 %cmp, i32 %b, i32 %c
%cond = icmp sgt i32 %a, -1
br i1 %cond, label %if.then, label %if.else
if.then:
ret i32 %retval
if.else:
ret i32 %retval
}

!0 = !{}