[SimplifyCFG] Fold the contiguous wrapping cases into ICmp. #161000
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@llvm/pr-subscribers-llvm-transforms Author: dianqk (dianqk) ChangesFixes #157113. Take the following IR as an example; we know the destination of the define i32 @<!-- -->src(i8 range(i8 0, 6) %arg) {
switch i8 %arg, label %else [
i8 0, label %if
i8 4, label %if
i8 5, label %if
]
if:
ret i32 0
else:
ret i32 1
}We can first try the non-wrapping range for both destinations, but I don't see how that would be any better. Proof: https://alive2.llvm.org/ce/z/acdWD4. Full diff: https://github.com/llvm/llvm-project/pull/161000.diff 2 Files Affected:
diff --git a/llvm/lib/Transforms/Utils/SimplifyCFG.cpp b/llvm/lib/Transforms/Utils/SimplifyCFG.cpp
index 5e719c6c8cbb7..b02aed3f8f5ea 100644
--- a/llvm/lib/Transforms/Utils/SimplifyCFG.cpp
+++ b/llvm/lib/Transforms/Utils/SimplifyCFG.cpp
@@ -5761,15 +5761,49 @@ bool SimplifyCFGOpt::simplifyUnreachable(UnreachableInst *UI) {
return Changed;
}
-static bool casesAreContiguous(SmallVectorImpl<ConstantInt *> &Cases) {
+static bool casesAreContiguous(Value *Condition,
+ SmallVectorImpl<ConstantInt *> &Cases,
+ ConstantInt *&ContiguousCasesMin,
+ ConstantInt *&ContiguousCasesMax,
+ bool &IsWrapping) {
assert(Cases.size() >= 1);
array_pod_sort(Cases.begin(), Cases.end(), constantIntSortPredicate);
- for (size_t I = 1, E = Cases.size(); I != E; ++I) {
- if (Cases[I - 1]->getValue() != Cases[I]->getValue() + 1)
+ auto Min = Cases.back()->getValue();
+ auto Max = Cases.front()->getValue();
+ auto Offset = Max - Min;
+ auto ContiguousOffset = Cases.size() - 1;
+ if (Offset == ContiguousOffset) {
+ ContiguousCasesMin = Cases.back();
+ ContiguousCasesMax = Cases.front();
+ return true;
+ }
+ ConstantRange CR = computeConstantRange(Condition, /*ForSigned=*/false);
+ // If this is a wrapping contiguous range, that is, [Min, OtherMin] +
+ // [OtherMax, Max] (also [OtherMax, OtherMin]), [OtherMin+1, OtherMax-1] is a
+ // contiguous range for the other destination. N.B. If CR is not a full range,
+ // Max+1 is not equal to Min. It's not continuous in arithmetic.
+ if (Max == CR.getUnsignedMax() && Min == CR.getUnsignedMin()) {
+ assert(Cases.size() >= 2);
+ auto *It =
+ std::adjacent_find(Cases.begin(), Cases.end(), [](auto L, auto R) {
+ return L->getValue() != R->getValue() + 1;
+ });
+ if (It == Cases.end())
return false;
+ auto *OtherMax = *It;
+ auto *OtherMin = *(It + 1);
+ if ((Max - OtherMax->getValue()) + (OtherMin->getValue() - Min) ==
+ Cases.size() - 2) {
+ ContiguousCasesMin = cast<ConstantInt>(
+ ConstantInt::get(OtherMin->getType(), OtherMin->getValue() + 1));
+ ContiguousCasesMax = cast<ConstantInt>(
+ ConstantInt::get(OtherMax->getType(), OtherMax->getValue() - 1));
+ IsWrapping = true;
+ return true;
+ }
}
- return true;
+ return false;
}
static void createUnreachableSwitchDefault(SwitchInst *Switch,
@@ -5840,25 +5874,34 @@ bool SimplifyCFGOpt::turnSwitchRangeIntoICmp(SwitchInst *SI,
assert(!CasesA.empty() || HasDefault);
// Figure out if one of the sets of cases form a contiguous range.
- SmallVectorImpl<ConstantInt *> *ContiguousCases = nullptr;
+ ConstantInt *ContiguousCasesMin = nullptr;
+ ConstantInt *ContiguousCasesMax = nullptr;
BasicBlock *ContiguousDest = nullptr;
BasicBlock *OtherDest = nullptr;
- if (!CasesA.empty() && casesAreContiguous(CasesA)) {
- ContiguousCases = &CasesA;
+ bool IsWrapping = false;
+ if (!CasesA.empty() &&
+ casesAreContiguous(SI->getCondition(), CasesA, ContiguousCasesMin,
+ ContiguousCasesMax, IsWrapping)) {
ContiguousDest = DestA;
OtherDest = DestB;
- } else if (casesAreContiguous(CasesB)) {
- ContiguousCases = &CasesB;
+ } else if (casesAreContiguous(SI->getCondition(), CasesB, ContiguousCasesMin,
+ ContiguousCasesMax, IsWrapping)) {
ContiguousDest = DestB;
OtherDest = DestA;
} else
return false;
+ if (IsWrapping)
+ std::swap(ContiguousDest, OtherDest);
+
// Start building the compare and branch.
- Constant *Offset = ConstantExpr::getNeg(ContiguousCases->back());
- Constant *NumCases =
- ConstantInt::get(Offset->getType(), ContiguousCases->size());
+ auto ContiguousCasesSize =
+ (ContiguousCasesMax->getValue() - ContiguousCasesMin->getValue())
+ .getZExtValue() +
+ 1;
+ Constant *Offset = ConstantExpr::getNeg(ContiguousCasesMin);
+ Constant *NumCases = ConstantInt::get(Offset->getType(), ContiguousCasesSize);
Value *Sub = SI->getCondition();
if (!Offset->isNullValue())
@@ -5866,7 +5909,7 @@ bool SimplifyCFGOpt::turnSwitchRangeIntoICmp(SwitchInst *SI,
Value *Cmp;
// If NumCases overflowed, then all possible values jump to the successor.
- if (NumCases->isNullValue() && !ContiguousCases->empty())
+ if (NumCases->isNullValue() && ContiguousCasesSize != 0)
Cmp = ConstantInt::getTrue(SI->getContext());
else
Cmp = Builder.CreateICmpULT(Sub, NumCases, "switch");
@@ -5895,14 +5938,14 @@ bool SimplifyCFGOpt::turnSwitchRangeIntoICmp(SwitchInst *SI,
// Prune obsolete incoming values off the successors' PHI nodes.
for (auto BBI = ContiguousDest->begin(); isa<PHINode>(BBI); ++BBI) {
- unsigned PreviousEdges = ContiguousCases->size();
+ unsigned PreviousEdges = ContiguousCasesSize;
if (ContiguousDest == SI->getDefaultDest())
++PreviousEdges;
for (unsigned I = 0, E = PreviousEdges - 1; I != E; ++I)
cast<PHINode>(BBI)->removeIncomingValue(SI->getParent());
}
for (auto BBI = OtherDest->begin(); isa<PHINode>(BBI); ++BBI) {
- unsigned PreviousEdges = SI->getNumCases() - ContiguousCases->size();
+ unsigned PreviousEdges = SI->getNumCases() - ContiguousCasesSize;
if (OtherDest == SI->getDefaultDest())
++PreviousEdges;
for (unsigned I = 0, E = PreviousEdges - 1; I != E; ++I)
diff --git a/llvm/test/Transforms/SimplifyCFG/switch-range-to-icmp.ll b/llvm/test/Transforms/SimplifyCFG/switch-range-to-icmp.ll
index 8f2ae2d054f1e..c6904fe273f09 100644
--- a/llvm/test/Transforms/SimplifyCFG/switch-range-to-icmp.ll
+++ b/llvm/test/Transforms/SimplifyCFG/switch-range-to-icmp.ll
@@ -188,4 +188,97 @@ exit:
ret void
}
+define i32 @wrapping_known_range(i8 range(i8 0, 6) %arg) {
+; CHECK-LABEL: @wrapping_known_range(
+; CHECK-NEXT: [[ARG_OFF:%.*]] = add i8 [[ARG:%.*]], -1
+; CHECK-NEXT: [[SWITCH:%.*]] = icmp ult i8 [[ARG_OFF]], 3
+; CHECK-NEXT: br i1 [[SWITCH]], label [[ELSE:%.*]], label [[IF:%.*]]
+; CHECK: common.ret:
+; CHECK-NEXT: [[COMMON_RET_OP:%.*]] = phi i32 [ [[I0:%.*]], [[IF]] ], [ [[I1:%.*]], [[ELSE]] ]
+; CHECK-NEXT: ret i32 [[COMMON_RET_OP]]
+; CHECK: if:
+; CHECK-NEXT: [[I0]] = call i32 @f(i32 0)
+; CHECK-NEXT: br label [[COMMON_RET:%.*]]
+; CHECK: else:
+; CHECK-NEXT: [[I1]] = call i32 @f(i32 1)
+; CHECK-NEXT: br label [[COMMON_RET]]
+;
+ switch i8 %arg, label %else [
+ i8 0, label %if
+ i8 4, label %if
+ i8 5, label %if
+ ]
+
+if:
+ %i0 = call i32 @f(i32 0)
+ ret i32 %i0
+
+else:
+ %i1 = call i32 @f(i32 1)
+ ret i32 %i1
+}
+
+define i32 @wrapping_range(i8 %arg) {
+; CHECK-LABEL: @wrapping_range(
+; CHECK-NEXT: [[ARG_OFF:%.*]] = add i8 [[ARG:%.*]], -1
+; CHECK-NEXT: [[SWITCH:%.*]] = icmp ult i8 [[ARG_OFF]], -4
+; CHECK-NEXT: br i1 [[SWITCH]], label [[ELSE:%.*]], label [[IF:%.*]]
+; CHECK: common.ret:
+; CHECK-NEXT: [[COMMON_RET_OP:%.*]] = phi i32 [ [[I0:%.*]], [[IF]] ], [ [[I1:%.*]], [[ELSE]] ]
+; CHECK-NEXT: ret i32 [[COMMON_RET_OP]]
+; CHECK: if:
+; CHECK-NEXT: [[I0]] = call i32 @f(i32 0)
+; CHECK-NEXT: br label [[COMMON_RET:%.*]]
+; CHECK: else:
+; CHECK-NEXT: [[I1]] = call i32 @f(i32 1)
+; CHECK-NEXT: br label [[COMMON_RET]]
+;
+ switch i8 %arg, label %else [
+ i8 0, label %if
+ i8 -3, label %if
+ i8 -2, label %if
+ i8 -1, label %if
+ ]
+
+if:
+ %i0 = call i32 @f(i32 0)
+ ret i32 %i0
+
+else:
+ %i1 = call i32 @f(i32 1)
+ ret i32 %i1
+}
+
+define i32 @no_continuous_wrapping_range(i8 %arg) {
+; CHECK-LABEL: @no_continuous_wrapping_range(
+; CHECK-NEXT: switch i8 [[ARG:%.*]], label [[ELSE:%.*]] [
+; CHECK-NEXT: i8 0, label [[IF:%.*]]
+; CHECK-NEXT: i8 -3, label [[IF]]
+; CHECK-NEXT: i8 -1, label [[IF]]
+; CHECK-NEXT: ]
+; CHECK: common.ret:
+; CHECK-NEXT: [[COMMON_RET_OP:%.*]] = phi i32 [ [[I0:%.*]], [[IF]] ], [ [[I1:%.*]], [[ELSE]] ]
+; CHECK-NEXT: ret i32 [[COMMON_RET_OP]]
+; CHECK: if:
+; CHECK-NEXT: [[I0]] = call i32 @f(i32 0)
+; CHECK-NEXT: br label [[COMMON_RET:%.*]]
+; CHECK: else:
+; CHECK-NEXT: [[I1]] = call i32 @f(i32 1)
+; CHECK-NEXT: br label [[COMMON_RET]]
+;
+ switch i8 %arg, label %else [
+ i8 0, label %if
+ i8 -3, label %if
+ i8 -1, label %if
+ ]
+
+if:
+ %i0 = call i32 @f(i32 0)
+ ret i32 %i0
+
+else:
+ %i1 = call i32 @f(i32 1)
+ ret i32 %i1
+}
+
declare void @bar(ptr nonnull dereferenceable(4))
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Fixes #157113.
Take the following IR as an example; we know the destination of the
[1, 3]cases is%else.We can first try the non-wrapping range for both destinations, but I don't see how that would be any better.
Proof: https://alive2.llvm.org/ce/z/acdWD4.