[llvm] [ConstraintElim] Handle switch cases with the same destination (PR #76928)
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Thu Jan 4 01:28:07 PST 2024
llvmbot wrote:
<!--LLVM PR SUMMARY COMMENT-->
@llvm/pr-subscribers-llvm-transforms
Author: Yingwei Zheng (dtcxzyw)
<details>
<summary>Changes</summary>
The original implementation only adds the fact `cond == C` if BB dominates DestBB and there is a unique edge from BB to DestBB.
This patch adds more range information for switch cases with the same destination if BB is the unique predecessor of DestBB.
The original motivation of this patch is to optimize a pattern in cvc5. For example:
```
%bf.load.i = load i16, ptr %d_kind.i, align 8
%bf.clear.i = and i16 %bf.load.i, 1023
%bf.cast.i = zext nneg i16 %bf.clear.i to i32
switch i32 %bf.cast.i, label %if.else [
i32 335, label %if.then
i32 303, label %if.then
]
if.then: ; preds = %entry, %entry
%d_children.i.i = getelementptr inbounds %"class.cvc5::internal::expr::NodeValue", ptr %0, i64 0, i32 3
%cmp.i.i.i.i.i = icmp eq i16 %bf.clear.i, 1023
%cond.i.i.i.i.i = select i1 %cmp.i.i.i.i.i, i32 -1, i32 %bf.cast.i
```
`%cmp.i.i.i.i.i` always evaluates to false because `%bf.clear.i` can only be 335 or 303.
Compile-time impact: http://llvm-compile-time-tracker.com/compare.php?from=8c72ff716b3e4b298695fa3faf6add860c6dbcb2&to=24a93e6c04b60b5d7d567379b8a0cd082c6554b0&stat=instructions%3Au
|stage1-O3|stage1-ReleaseThinLTO|stage1-ReleaseLTO-g|stage1-O0-g|stage2-O3|stage2-O0-g|stage2-clang|
|--|--|--|--|--|--|--|
|-0.00%|+0.02%|+0.01%|+0.03%|-0.05%|+0.03%|+0.02%|
---
Full diff: https://github.com/llvm/llvm-project/pull/76928.diff
2 Files Affected:
- (modified) llvm/lib/Transforms/Scalar/ConstraintElimination.cpp (+42-6)
- (modified) llvm/test/Transforms/ConstraintElimination/switch.ll (+113-4)
``````````diff
diff --git a/llvm/lib/Transforms/Scalar/ConstraintElimination.cpp b/llvm/lib/Transforms/Scalar/ConstraintElimination.cpp
index cc93c8617c05e2..59c23ea5993f6f 100644
--- a/llvm/lib/Transforms/Scalar/ConstraintElimination.cpp
+++ b/llvm/lib/Transforms/Scalar/ConstraintElimination.cpp
@@ -1057,13 +1057,49 @@ void State::addInfoFor(BasicBlock &BB) {
}
if (auto *Switch = dyn_cast<SwitchInst>(BB.getTerminator())) {
- for (auto &Case : Switch->cases()) {
- BasicBlock *Succ = Case.getCaseSuccessor();
- Value *V = Case.getCaseValue();
- if (!canAddSuccessor(BB, Succ))
+ DenseMap<BasicBlock *, SmallVector<ConstantInt *>> BBMap;
+ for (auto &Case : Switch->cases())
+ BBMap[Case.getCaseSuccessor()].push_back(Case.getCaseValue());
+ // TODO: handle default dest
+ BBMap.erase(Switch->getDefaultDest());
+ Value *Cond = Switch->getCondition();
+ Type *Ty = Switch->getCondition()->getType();
+ unsigned BitWidth = Ty->getScalarSizeInBits();
+ for (auto &[Succ, Values] : BBMap) {
+ if (Succ->getUniquePredecessor() != &BB)
continue;
- WorkList.emplace_back(FactOrCheck::getConditionFact(
- DT.getNode(Succ), CmpInst::ICMP_EQ, Switch->getCondition(), V));
+ DomTreeNode *Node = DT.getNode(Succ);
+ if (Values.size() == 1)
+ WorkList.emplace_back(FactOrCheck::getConditionFact(
+ Node, CmpInst::ICMP_EQ, Cond, Values.back()));
+ else {
+ APInt SignedMin = APInt::getSignedMaxValue(BitWidth);
+ APInt SignedMax = APInt::getSignedMinValue(BitWidth);
+ APInt UnsignedMin = APInt::getMaxValue(BitWidth);
+ APInt UnsignedMax = APInt::getMinValue(BitWidth);
+
+ for (ConstantInt *V : Values) {
+ const APInt &C = V->getValue();
+ SignedMin = APIntOps::smin(SignedMin, C);
+ SignedMax = APIntOps::smax(SignedMax, C);
+ UnsignedMin = APIntOps::umin(UnsignedMin, C);
+ UnsignedMax = APIntOps::umax(UnsignedMax, C);
+ }
+ if (!SignedMin.isMinSignedValue())
+ WorkList.emplace_back(FactOrCheck::getConditionFact(
+ Node, CmpInst::ICMP_SGE, Cond, ConstantInt::get(Ty, SignedMin)));
+ if (!SignedMax.isMaxSignedValue())
+ WorkList.emplace_back(FactOrCheck::getConditionFact(
+ Node, CmpInst::ICMP_SLE, Cond, ConstantInt::get(Ty, SignedMax)));
+ if (!UnsignedMin.isMinValue())
+ WorkList.emplace_back(
+ FactOrCheck::getConditionFact(Node, CmpInst::ICMP_UGE, Cond,
+ ConstantInt::get(Ty, UnsignedMin)));
+ if (!UnsignedMax.isMaxValue())
+ WorkList.emplace_back(
+ FactOrCheck::getConditionFact(Node, CmpInst::ICMP_ULE, Cond,
+ ConstantInt::get(Ty, UnsignedMax)));
+ }
}
return;
}
diff --git a/llvm/test/Transforms/ConstraintElimination/switch.ll b/llvm/test/Transforms/ConstraintElimination/switch.ll
index b104b26e83cff2..fd581d081b4d3b 100644
--- a/llvm/test/Transforms/ConstraintElimination/switch.ll
+++ b/llvm/test/Transforms/ConstraintElimination/switch.ll
@@ -151,10 +151,8 @@ define i1 @switch_same_destination_for_different_cases(i8 %x) {
; CHECK: exit.2:
; CHECK-NEXT: [[C_3:%.*]] = icmp ult i8 [[X]], 7
; CHECK-NEXT: call void @use(i1 [[C_3]])
-; CHECK-NEXT: [[C_4:%.*]] = icmp ult i8 [[X]], 6
-; CHECK-NEXT: call void @use(i1 [[C_4]])
-; CHECK-NEXT: [[C_5:%.*]] = icmp ult i8 [[X]], 11
-; CHECK-NEXT: call void @use(i1 [[C_5]])
+; CHECK-NEXT: call void @use(i1 false)
+; CHECK-NEXT: call void @use(i1 true)
; CHECK-NEXT: [[C_6:%.*]] = icmp ult i8 [[X]], 10
; CHECK-NEXT: ret i1 [[C_6]]
;
@@ -181,4 +179,115 @@ exit.2:
ret i1 %c.6
}
+define i1 @test_switch_with_same_dest(i32 %a) {
+; CHECK-LABEL: @test_switch_with_same_dest(
+; CHECK-NEXT: entry:
+; CHECK-NEXT: [[B:%.*]] = and i32 [[A:%.*]], 1023
+; CHECK-NEXT: switch i32 [[B]], label [[SW_DEFAULT:%.*]] [
+; CHECK-NEXT: i32 37, label [[SW_BB:%.*]]
+; CHECK-NEXT: i32 38, label [[SW_BB]]
+; CHECK-NEXT: ]
+; CHECK: sw.bb:
+; CHECK-NEXT: ret i1 false
+; CHECK: sw.default:
+; CHECK-NEXT: ret i1 false
+;
+entry:
+ %b = and i32 %a, 1023
+ switch i32 %b, label %sw.default [
+ i32 37, label %sw.bb
+ i32 38, label %sw.bb
+ ]
+
+sw.bb:
+ %cmp = icmp eq i32 %b, 1023
+ ret i1 %cmp
+sw.default:
+ ret i1 false
+}
+
+define i1 @test_switch_with_same_dest_zext(i16 %a) {
+; CHECK-LABEL: @test_switch_with_same_dest_zext(
+; CHECK-NEXT: entry:
+; CHECK-NEXT: [[B:%.*]] = and i16 [[A:%.*]], 1023
+; CHECK-NEXT: [[B_EXT:%.*]] = zext nneg i16 [[B]] to i32
+; CHECK-NEXT: switch i32 [[B_EXT]], label [[SW_DEFAULT:%.*]] [
+; CHECK-NEXT: i32 37, label [[SW_BB:%.*]]
+; CHECK-NEXT: i32 38, label [[SW_BB]]
+; CHECK-NEXT: ]
+; CHECK: sw.bb:
+; CHECK-NEXT: ret i1 false
+; CHECK: sw.default:
+; CHECK-NEXT: ret i1 false
+;
+entry:
+ %b = and i16 %a, 1023
+ %b.ext = zext nneg i16 %b to i32
+ switch i32 %b.ext, label %sw.default [
+ i32 37, label %sw.bb
+ i32 38, label %sw.bb
+ ]
+
+sw.bb:
+ %cmp = icmp eq i16 %b, 1023
+ ret i1 %cmp
+sw.default:
+ ret i1 false
+}
+
+; Negative tests
+
+define i1 @test_switch_with_same_dest_fail1(i32 %a) {
+; CHECK-LABEL: @test_switch_with_same_dest_fail1(
+; CHECK-NEXT: entry:
+; CHECK-NEXT: [[B:%.*]] = and i32 [[A:%.*]], 1023
+; CHECK-NEXT: switch i32 [[B]], label [[SW_BB:%.*]] [
+; CHECK-NEXT: i32 37, label [[SW_BB]]
+; CHECK-NEXT: i32 38, label [[SW_BB]]
+; CHECK-NEXT: ]
+; CHECK: sw.bb:
+; CHECK-NEXT: [[CMP:%.*]] = icmp eq i32 [[B]], 1023
+; CHECK-NEXT: ret i1 [[CMP]]
+;
+entry:
+ %b = and i32 %a, 1023
+ switch i32 %b, label %sw.bb [
+ i32 37, label %sw.bb
+ i32 38, label %sw.bb
+ ]
+
+sw.bb:
+ %cmp = icmp eq i32 %b, 1023
+ ret i1 %cmp
+}
+
+define i1 @test_switch_with_same_dest_fail2(i32 %a, i1 %cond) {
+; CHECK-LABEL: @test_switch_with_same_dest_fail2(
+; CHECK-NEXT: entry:
+; CHECK-NEXT: [[B:%.*]] = and i32 [[A:%.*]], 1023
+; CHECK-NEXT: br i1 [[COND:%.*]], label [[IF_THEN:%.*]], label [[SW_BB:%.*]]
+; CHECK: if.then:
+; CHECK-NEXT: switch i32 [[B]], label [[SW_BB]] [
+; CHECK-NEXT: i32 37, label [[SW_BB]]
+; CHECK-NEXT: i32 38, label [[SW_BB]]
+; CHECK-NEXT: ]
+; CHECK: sw.bb:
+; CHECK-NEXT: [[CMP:%.*]] = icmp eq i32 [[B]], 1023
+; CHECK-NEXT: ret i1 [[CMP]]
+;
+entry:
+ %b = and i32 %a, 1023
+ br i1 %cond, label %if.then, label %sw.bb
+
+if.then:
+ switch i32 %b, label %sw.bb [
+ i32 37, label %sw.bb
+ i32 38, label %sw.bb
+ ]
+
+sw.bb:
+ %cmp = icmp eq i32 %b, 1023
+ ret i1 %cmp
+}
+
declare void @use(i1)
``````````
</details>
https://github.com/llvm/llvm-project/pull/76928
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