[llvm] [ConstraintElim] Generalize IV logic to chain of exiting blocks. (PR #108031)
Florian Hahn via llvm-commits
llvm-commits at lists.llvm.org
Tue Sep 10 09:24:33 PDT 2024
https://github.com/fhahn updated https://github.com/llvm/llvm-project/pull/108031
>From a5fd3c91a4e46d103c43c39b2a56b73725fb5187 Mon Sep 17 00:00:00 2001
From: Florian Hahn <flo at fhahn.com>
Date: Mon, 9 Sep 2024 14:35:43 +0100
Subject: [PATCH 1/2] [ConstraintElim] Generalize IV logic to chain of exiting
blocks.
Generalize the logic to add facts for inductions in the header block to
any chain of exiting blocks starting at the header.
Such IR is for generated by Swift for a number of loops with runtime
checks.
The logic could probably generalized further.
---
.../Scalar/ConstraintElimination.cpp | 47 ++++++++++++++-----
.../monotonic-pointer-phis-chain-of-exits.ll | 12 ++---
2 files changed, 39 insertions(+), 20 deletions(-)
diff --git a/llvm/lib/Transforms/Scalar/ConstraintElimination.cpp b/llvm/lib/Transforms/Scalar/ConstraintElimination.cpp
index 6565aed4bc390c..08fe5b2aa1ff2c 100644
--- a/llvm/lib/Transforms/Scalar/ConstraintElimination.cpp
+++ b/llvm/lib/Transforms/Scalar/ConstraintElimination.cpp
@@ -193,10 +193,14 @@ struct State {
/// Process block \p BB and add known facts to work-list.
void addInfoFor(BasicBlock &BB);
- /// Try to add facts for loop inductions (AddRecs) in EQ/NE compares
- /// controlling the loop header.
+ /// Try to add facts for loop inductions (AddRecs) from EQ/NE compares
+ /// controlling loop exits.
void addInfoForInductions(BasicBlock &BB);
+ /// Try to add facts for loop inductions (AddRecs) from \p Cond which controls
+ /// an exit from \p L.
+ void addInfoForInduction(ICmpInst *Cond, Loop *L);
+
/// Returns true if we can add a known condition from BB to its successor
/// block Succ.
bool canAddSuccessor(BasicBlock &BB, BasicBlock *Succ) const {
@@ -900,18 +904,14 @@ static void dumpConstraint(ArrayRef<int64_t> C,
}
#endif
-void State::addInfoForInductions(BasicBlock &BB) {
- auto *L = LI.getLoopFor(&BB);
- if (!L || L->getHeader() != &BB)
- return;
-
+void State::addInfoForInduction(ICmpInst *Cond, Loop *L) {
Value *A;
Value *B;
CmpInst::Predicate Pred;
- if (!match(BB.getTerminator(),
- m_Br(m_ICmp(Pred, m_Value(A), m_Value(B)), m_Value(), m_Value())))
+ if (!match(Cond, m_ICmp(Pred, m_Value(A), m_Value(B))))
return;
+
PHINode *PN = dyn_cast<PHINode>(A);
if (!PN) {
Pred = CmpInst::getSwappedPredicate(Pred);
@@ -919,10 +919,11 @@ void State::addInfoForInductions(BasicBlock &BB) {
PN = dyn_cast<PHINode>(A);
}
- if (!PN || PN->getParent() != &BB || PN->getNumIncomingValues() != 2 ||
- !SE.isSCEVable(PN->getType()))
+ if (!PN || PN->getParent() != L->getHeader() ||
+ PN->getNumIncomingValues() != 2 || !SE.isSCEVable(PN->getType()))
return;
+ BasicBlock &BB = *Cond->getParent();
BasicBlock *InLoopSucc = nullptr;
if (Pred == CmpInst::ICMP_NE)
InLoopSucc = cast<BranchInst>(BB.getTerminator())->getSuccessor(0);
@@ -931,6 +932,8 @@ void State::addInfoForInductions(BasicBlock &BB) {
else
return;
+ assert(InLoopSucc != L->getHeader() &&
+ "Cannot inject condition back to loop header");
if (!L->contains(InLoopSucc) || !L->isLoopExiting(&BB) || InLoopSucc == &BB)
return;
@@ -1048,6 +1051,28 @@ void State::addInfoForInductions(BasicBlock &BB) {
}
}
+void State::addInfoForInductions(BasicBlock &BB) {
+ auto *L = LI.getLoopFor(&BB);
+ if (!L)
+ return;
+ if (L->getHeader() != &BB)
+ return;
+
+ BasicBlock *Curr = &BB;
+ while (L->isLoopExiting(Curr)) {
+ // Don't try to add condition from latch to loop header.
+ if (L->isLoopLatch(Curr))
+ break;
+ auto *Term = dyn_cast<BranchInst>(Curr->getTerminator());
+ if (!Term)
+ break;
+ if (isa<ICmpInst>(Term->getCondition()))
+ addInfoForInduction(cast<ICmpInst>(Term->getCondition()), L);
+ Curr = L->contains(Term->getSuccessor(0)) ? Term->getSuccessor(0)
+ : Term->getSuccessor(1);
+ }
+}
+
void State::addInfoFor(BasicBlock &BB) {
addInfoForInductions(BB);
diff --git a/llvm/test/Transforms/ConstraintElimination/monotonic-pointer-phis-chain-of-exits.ll b/llvm/test/Transforms/ConstraintElimination/monotonic-pointer-phis-chain-of-exits.ll
index 6b128d9e525ca3..a2673bd8e73efb 100644
--- a/llvm/test/Transforms/ConstraintElimination/monotonic-pointer-phis-chain-of-exits.ll
+++ b/llvm/test/Transforms/ConstraintElimination/monotonic-pointer-phis-chain-of-exits.ll
@@ -25,9 +25,7 @@ define void @test_monotonic_ptr_iv_inc_1_different_element_types_1_chain_of_2_ex
; CHECK-NEXT: [[C_2:%.*]] = call i1 @cond()
; CHECK-NEXT: br i1 [[C_2]], label [[LOOP_NEXT:%.*]], label [[EXIT]]
; CHECK: loop.next:
-; CHECK-NEXT: [[T_1:%.*]] = icmp uge ptr [[PTR_IV]], [[START]]
-; CHECK-NEXT: [[T_2:%.*]] = icmp ult ptr [[PTR_IV]], [[UPPER]]
-; CHECK-NEXT: [[AND:%.*]] = and i1 [[T_1]], [[T_2]]
+; CHECK-NEXT: [[AND:%.*]] = and i1 true, true
; CHECK-NEXT: br i1 [[AND]], label [[LOOP_LATCH]], label [[EXIT]]
; CHECK: loop.latch:
; CHECK-NEXT: call void @use(ptr [[PTR_IV]])
@@ -94,9 +92,7 @@ define void @test_monotonic_ptr_iv_inc_1_different_element_types_1_chain_of_3_ex
; CHECK-NEXT: [[C_2:%.*]] = call i1 @cond()
; CHECK-NEXT: br i1 [[C_2]], label [[LOOP_NEXT:%.*]], label [[EXIT]]
; CHECK: loop.next:
-; CHECK-NEXT: [[T_1:%.*]] = icmp uge ptr [[PTR_IV]], [[START]]
-; CHECK-NEXT: [[T_2:%.*]] = icmp ult ptr [[PTR_IV]], [[UPPER]]
-; CHECK-NEXT: [[AND:%.*]] = and i1 [[T_1]], [[T_2]]
+; CHECK-NEXT: [[AND:%.*]] = and i1 true, true
; CHECK-NEXT: br i1 [[AND]], label [[LOOP_LATCH]], label [[EXIT]]
; CHECK: loop.latch:
; CHECK-NEXT: call void @use(ptr [[PTR_IV]])
@@ -163,9 +159,7 @@ define void @test_monotonic_ptr_iv_inc_1_different_element_types_1_chain_of_2_ex
; CHECK-NEXT: [[C_2:%.*]] = call i1 @cond()
; CHECK-NEXT: br i1 [[C_2]], label [[LOOP_NEXT:%.*]], label [[EXIT]]
; CHECK: loop.next:
-; CHECK-NEXT: [[T_1:%.*]] = icmp uge ptr [[PTR_IV]], [[START]]
-; CHECK-NEXT: [[T_2:%.*]] = icmp ult ptr [[PTR_IV]], [[UPPER]]
-; CHECK-NEXT: [[AND:%.*]] = and i1 [[T_1]], [[T_2]]
+; CHECK-NEXT: [[AND:%.*]] = and i1 true, true
; CHECK-NEXT: br i1 [[AND]], label [[LOOP_LATCH]], label [[EXIT]]
; CHECK: loop.latch:
; CHECK-NEXT: call void @use(ptr [[PTR_IV]])
>From 0a7728b2a9ad4dab87f7829b72de16fd4f38f7e9 Mon Sep 17 00:00:00 2001
From: Florian Hahn <flo at fhahn.com>
Date: Tue, 10 Sep 2024 17:23:29 +0100
Subject: [PATCH 2/2] !fixup address latest comments, thanks!
---
llvm/lib/Transforms/Scalar/ConstraintElimination.cpp | 8 +++++---
1 file changed, 5 insertions(+), 3 deletions(-)
diff --git a/llvm/lib/Transforms/Scalar/ConstraintElimination.cpp b/llvm/lib/Transforms/Scalar/ConstraintElimination.cpp
index 08fe5b2aa1ff2c..deb1592b0c147e 100644
--- a/llvm/lib/Transforms/Scalar/ConstraintElimination.cpp
+++ b/llvm/lib/Transforms/Scalar/ConstraintElimination.cpp
@@ -932,9 +932,11 @@ void State::addInfoForInduction(ICmpInst *Cond, Loop *L) {
else
return;
+ assert(L->isLoopExiting(&BB) &&
+ "Most be called with a condition in a loop-exiting block");
assert(InLoopSucc != L->getHeader() &&
"Cannot inject condition back to loop header");
- if (!L->contains(InLoopSucc) || !L->isLoopExiting(&BB) || InLoopSucc == &BB)
+ if (!L->contains(InLoopSucc) || InLoopSucc == &BB)
return;
auto *AR = dyn_cast_or_null<SCEVAddRecExpr>(SE.getSCEV(PN));
@@ -1066,8 +1068,8 @@ void State::addInfoForInductions(BasicBlock &BB) {
auto *Term = dyn_cast<BranchInst>(Curr->getTerminator());
if (!Term)
break;
- if (isa<ICmpInst>(Term->getCondition()))
- addInfoForInduction(cast<ICmpInst>(Term->getCondition()), L);
+ if (auto *CmpI = dyn_cast<ICmpInst>(Term->getCondition()))
+ addInfoForInduction(CmpI, L);
Curr = L->contains(Term->getSuccessor(0)) ? Term->getSuccessor(0)
: Term->getSuccessor(1);
}
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