[llvm] b952148 - [LSR] Rewrite IV match for term-fold using existing utilities
Philip Reames via llvm-commits
llvm-commits at lists.llvm.org
Mon Mar 20 10:41:07 PDT 2023
Author: Philip Reames
Date: 2023-03-20T10:41:01-07:00
New Revision: b9521484ec72142bce8124a171206fc577abfd3f
URL: https://github.com/llvm/llvm-project/commit/b9521484ec72142bce8124a171206fc577abfd3f
DIFF: https://github.com/llvm/llvm-project/commit/b9521484ec72142bce8124a171206fc577abfd3f.diff
LOG: [LSR] Rewrite IV match for term-fold using existing utilities
Main benefit here is making the logic easier to follow, slightly more efficient, and more in line with LFTR. This is not NFC. There are three semantic changes here.
First, we drop handling for constants on the LHS of the comparison. These are non-canonical, and we're very late in the optimization pipeline here, so there's no point in supporting this. I removed a test which covered this case.
Second, we don't need the almost dead IV to be an addrec. We just need SCEV to be able to compute a trip count for it.
Third, we require a simple IV for the almost dead IV. In theory, this removes cases we could have previously handled, but given a) zero testing and b) multiple known correctness issues, I'm adopting an attidute of narrowing this down to something which works correctly, and *then* expanding.
Added:
Modified:
llvm/lib/Transforms/Scalar/LoopStrengthReduce.cpp
llvm/test/Transforms/LoopStrengthReduce/lsr-term-fold-negative-testcase.ll
llvm/test/Transforms/LoopStrengthReduce/lsr-term-fold.ll
Removed:
################################################################################
diff --git a/llvm/lib/Transforms/Scalar/LoopStrengthReduce.cpp b/llvm/lib/Transforms/Scalar/LoopStrengthReduce.cpp
index 5ff7c1027108..5d8e822eaddf 100644
--- a/llvm/lib/Transforms/Scalar/LoopStrengthReduce.cpp
+++ b/llvm/lib/Transforms/Scalar/LoopStrengthReduce.cpp
@@ -6719,49 +6719,23 @@ canFoldTermCondOfLoop(Loop *L, ScalarEvolution &SE, DominatorTree &DT,
return std::nullopt;
}
- // For `IsToFold`, a primary IV can be replaced by other affine AddRec when it
- // is only used by the terminating condition. To check for this, we may need
- // to traverse through a chain of use-def until we can examine the final
- // usage.
- // *----------------------*
- // *---->| LoopHeader: |
- // | | PrimaryIV = phi ... |
- // | *----------------------*
- // | |
- // | |
- // | chain of
- // | single use
- // used by |
- // phi |
- // | Value
- // | / \
- // | chain of chain of
- // | single use single use
- // | / \
- // | / \
- // *- Value Value --> used by terminating condition
- auto IsToFold = [&](PHINode &PN) -> bool {
- Value *V = &PN;
-
- while (V->getNumUses() == 1)
- V = *V->user_begin();
-
- if (V->getNumUses() != 2)
- return false;
+ BinaryOperator *LHS = dyn_cast<BinaryOperator>(TermCond->getOperand(0));
+ Value *RHS = TermCond->getOperand(1);
+ if (!LHS || !L->isLoopInvariant(RHS))
+ // We could pattern match the inverse form of the icmp, but that is
+ // non-canonical, and this pass is running *very* late in the pipeline.
+ return std::nullopt;
- Value *VToPN = nullptr;
- Value *VToTermCond = nullptr;
- for (User *U : V->users()) {
- while (U->getNumUses() == 1) {
- if (isa<PHINode>(U))
- VToPN = U;
- if (U == TermCond)
- VToTermCond = U;
- U = *U->user_begin();
- }
- }
- return VToPN && VToTermCond;
- };
+ // Find the IV used by the current exit condition.
+ PHINode *ToFold;
+ Value *ToFoldStart, *ToFoldStep;
+ if (!matchSimpleRecurrence(LHS, ToFold, ToFoldStart, ToFoldStep))
+ return std::nullopt;
+
+ // If that IV isn't dead after we rewrite the exit condition in terms of
+ // another IV, there's no point in doing the transform.
+ if (!isAlmostDeadIV(ToFold, LoopLatch, TermCond))
+ return std::nullopt;
// If this is an IV which we could replace the terminating condition, return
// the final value of the alternative IV on the last iteration.
@@ -6789,11 +6763,13 @@ canFoldTermCondOfLoop(Loop *L, ScalarEvolution &SE, DominatorTree &DT,
return TermValueS;
};
- PHINode *ToFold = nullptr;
PHINode *ToHelpFold = nullptr;
const SCEV *TermValueS = nullptr;
for (PHINode &PN : L->getHeader()->phis()) {
+ if (ToFold == &PN)
+ continue;
+
if (!SE.isSCEVable(PN.getType())) {
LLVM_DEBUG(dbgs() << "IV of phi '" << PN
<< "' is not SCEV-able, not qualified for the "
@@ -6809,9 +6785,7 @@ canFoldTermCondOfLoop(Loop *L, ScalarEvolution &SE, DominatorTree &DT,
continue;
}
- if (IsToFold(PN))
- ToFold = &PN;
- else if (auto P = getAlternateIVEnd(PN)) {
+ if (auto P = getAlternateIVEnd(PN)) {
ToHelpFold = &PN;
TermValueS = P;
}
diff --git a/llvm/test/Transforms/LoopStrengthReduce/lsr-term-fold-negative-testcase.ll b/llvm/test/Transforms/LoopStrengthReduce/lsr-term-fold-negative-testcase.ll
index 8682351a4e30..1b9b58f79b48 100644
--- a/llvm/test/Transforms/LoopStrengthReduce/lsr-term-fold-negative-testcase.ll
+++ b/llvm/test/Transforms/LoopStrengthReduce/lsr-term-fold-negative-testcase.ll
@@ -106,15 +106,14 @@ define void @NonAddRecIV(ptr %a) {
; CHECK-SAME: (ptr [[A:%.*]]) {
; CHECK-NEXT: entry:
; CHECK-NEXT: [[UGLYGEP:%.*]] = getelementptr i8, ptr [[A]], i32 84
+; CHECK-NEXT: [[SCEVGEP:%.*]] = getelementptr i8, ptr [[A]], i64 148
; CHECK-NEXT: br label [[FOR_BODY:%.*]]
; CHECK: for.body:
; CHECK-NEXT: [[LSR_IV1:%.*]] = phi ptr [ [[UGLYGEP2:%.*]], [[FOR_BODY]] ], [ [[UGLYGEP]], [[ENTRY:%.*]] ]
-; CHECK-NEXT: [[LSR_IV:%.*]] = phi i32 [ [[LSR_IV_NEXT:%.*]], [[FOR_BODY]] ], [ 1, [[ENTRY]] ]
; CHECK-NEXT: store i32 1, ptr [[LSR_IV1]], align 4
-; CHECK-NEXT: [[LSR_IV_NEXT]] = mul nsw i32 [[LSR_IV]], 2
; CHECK-NEXT: [[UGLYGEP2]] = getelementptr i8, ptr [[LSR_IV1]], i64 4
-; CHECK-NEXT: [[EXITCOND_NOT:%.*]] = icmp eq i32 [[LSR_IV_NEXT]], 65536
-; CHECK-NEXT: br i1 [[EXITCOND_NOT]], label [[FOR_END:%.*]], label [[FOR_BODY]]
+; CHECK-NEXT: [[LSR_FOLD_TERM_COND_REPLACED_TERM_COND:%.*]] = icmp eq ptr [[UGLYGEP2]], [[SCEVGEP]]
+; CHECK-NEXT: br i1 [[LSR_FOLD_TERM_COND_REPLACED_TERM_COND]], label [[FOR_END:%.*]], label [[FOR_BODY]]
; CHECK: for.end:
; CHECK-NEXT: ret void
;
diff --git a/llvm/test/Transforms/LoopStrengthReduce/lsr-term-fold.ll b/llvm/test/Transforms/LoopStrengthReduce/lsr-term-fold.ll
index 7da1a73a21d1..a72e85979157 100644
--- a/llvm/test/Transforms/LoopStrengthReduce/lsr-term-fold.ll
+++ b/llvm/test/Transforms/LoopStrengthReduce/lsr-term-fold.ll
@@ -297,39 +297,6 @@ define void @IcmpSgt(ptr %a) {
; CHECK-LABEL: @IcmpSgt(
; CHECK-NEXT: entry:
; CHECK-NEXT: [[UGLYGEP:%.*]] = getelementptr i8, ptr [[A:%.*]], i32 84
-; CHECK-NEXT: [[SCEVGEP:%.*]] = getelementptr i8, ptr [[A]], i64 88
-; CHECK-NEXT: br label [[FOR_BODY:%.*]]
-; CHECK: for.body:
-; CHECK-NEXT: [[LSR_IV1:%.*]] = phi ptr [ [[UGLYGEP2:%.*]], [[FOR_BODY]] ], [ [[UGLYGEP]], [[ENTRY:%.*]] ]
-; CHECK-NEXT: store i32 1, ptr [[LSR_IV1]], align 4
-; CHECK-NEXT: [[UGLYGEP2]] = getelementptr i8, ptr [[LSR_IV1]], i32 4
-; CHECK-NEXT: [[LSR_FOLD_TERM_COND_REPLACED_TERM_COND:%.*]] = icmp eq ptr [[UGLYGEP2]], [[SCEVGEP]]
-; CHECK-NEXT: br i1 [[LSR_FOLD_TERM_COND_REPLACED_TERM_COND]], label [[FOR_END:%.*]], label [[FOR_BODY]]
-; CHECK: for.end:
-; CHECK-NEXT: ret void
-;
-entry:
- %uglygep = getelementptr i8, ptr %a, i32 84
- br label %for.body
-
-for.body: ; preds = %for.body, %entry
- %lsr.iv1 = phi ptr [ %uglygep2, %for.body ], [ %uglygep, %entry ]
- %lsr.iv = phi i32 [ %lsr.iv.next, %for.body ], [ 379, %entry ]
- store i32 1, ptr %lsr.iv1, align 4
- %lsr.iv.next = add nsw i32 %lsr.iv, -1
- %uglygep2 = getelementptr i8, ptr %lsr.iv1, i32 4
- %exitcond.not = icmp sgt i32 0, %lsr.iv.next
- br i1 %exitcond.not, label %for.body, label %for.end
-
-for.end: ; preds = %for.body
- ret void
-}
-
-; Invert predicate and branches
-define void @IcmpSgt2(ptr %a) {
-; CHECK-LABEL: @IcmpSgt2(
-; CHECK-NEXT: entry:
-; CHECK-NEXT: [[UGLYGEP:%.*]] = getelementptr i8, ptr [[A:%.*]], i32 84
; CHECK-NEXT: [[SCEVGEP:%.*]] = getelementptr i8, ptr [[A]], i64 1600
; CHECK-NEXT: br label [[FOR_BODY:%.*]]
; CHECK: for.body:
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