[llvm] 2934229 - [LoopInterchange] Fix legality for triangular loops
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llvm-commits at lists.llvm.org
Tue May 11 08:06:19 PDT 2021
Author: Congzhe Cao
Date: 2021-05-11T11:00:46-04:00
New Revision: 29342291d25b83da97e74d75004b177ba41114fc
URL: https://github.com/llvm/llvm-project/commit/29342291d25b83da97e74d75004b177ba41114fc
DIFF: https://github.com/llvm/llvm-project/commit/29342291d25b83da97e74d75004b177ba41114fc.diff
LOG: [LoopInterchange] Fix legality for triangular loops
This is a bug fix in legality check.
When we encounter triangular loops such as the following form:
for (int i = 0; i < m; i++)
for (int j = 0; j < i; j++), or
for (int i = 0; i < m; i++)
for (int j = 0; j*i < n; j++),
we should not perform interchange since the number of executions of the loop body
will be different before and after interchange, resulting in incorrect results.
Reviewed By: bmahjour
Differential Revision: https://reviews.llvm.org/D101305
Added:
llvm/test/Transforms/LoopInterchange/inner-indvar-depend-on-outer-indvar.ll
Modified:
llvm/lib/Transforms/Scalar/LoopInterchange.cpp
Removed:
################################################################################
diff --git a/llvm/lib/Transforms/Scalar/LoopInterchange.cpp b/llvm/lib/Transforms/Scalar/LoopInterchange.cpp
index 5aed49dccf820..58b456d5615fd 100644
--- a/llvm/lib/Transforms/Scalar/LoopInterchange.cpp
+++ b/llvm/lib/Transforms/Scalar/LoopInterchange.cpp
@@ -656,6 +656,65 @@ bool LoopInterchangeLegality::isLoopStructureUnderstood(
return false;
}
}
+
+ // TODO: Handle triangular loops of another form.
+ // e.g. for(int i=0;i<N;i++)
+ // for(int j=0;j<i;j++)
+ // or,
+ // for(int i=0;i<N;i++)
+ // for(int j=0;j*i<N;j++)
+ BasicBlock *InnerLoopLatch = InnerLoop->getLoopLatch();
+ BranchInst *InnerLoopLatchBI =
+ dyn_cast<BranchInst>(InnerLoopLatch->getTerminator());
+ if (!InnerLoopLatchBI->isConditional())
+ return false;
+ if (CmpInst *InnerLoopCmp =
+ dyn_cast<CmpInst>(InnerLoopLatchBI->getCondition())) {
+ Value *Op0 = InnerLoopCmp->getOperand(0);
+ Value *Op1 = InnerLoopCmp->getOperand(1);
+
+ // LHS and RHS of the inner loop exit condition, e.g.,
+ // in "for(int j=0;j<i;j++)", LHS is j and RHS is i.
+ Value *Left = nullptr;
+ Value *Right = nullptr;
+
+ // Check if V only involves inner loop induction variable.
+ // Return true if V is InnerInduction, or a cast from
+ // InnerInduction, or a binary operator that involves
+ // InnerInduction and a constant.
+ std::function<bool(Value *)> IsPathToIndVar;
+ IsPathToIndVar = [&InnerInduction, &IsPathToIndVar](Value *V) -> bool {
+ if (V == InnerInduction)
+ return true;
+ if (isa<Constant>(V))
+ return true;
+ Instruction *I = dyn_cast<Instruction>(V);
+ if (!I)
+ return false;
+ if (isa<CastInst>(I))
+ return IsPathToIndVar(I->getOperand(0));
+ if (isa<BinaryOperator>(I))
+ return IsPathToIndVar(I->getOperand(0)) &&
+ IsPathToIndVar(I->getOperand(1));
+ return false;
+ };
+
+ if (IsPathToIndVar(Op0) && !isa<Constant>(Op0)) {
+ Left = Op0;
+ Right = Op1;
+ } else if (IsPathToIndVar(Op1) && !isa<Constant>(Op1)) {
+ Left = Op1;
+ Right = Op0;
+ }
+
+ if (Left == nullptr)
+ return false;
+
+ const SCEV *S = SE->getSCEV(Right);
+ if (!SE->isLoopInvariant(S, OuterLoop))
+ return false;
+ }
+
return true;
}
diff --git a/llvm/test/Transforms/LoopInterchange/inner-indvar-depend-on-outer-indvar.ll b/llvm/test/Transforms/LoopInterchange/inner-indvar-depend-on-outer-indvar.ll
new file mode 100644
index 0000000000000..9a571acc47ec9
--- /dev/null
+++ b/llvm/test/Transforms/LoopInterchange/inner-indvar-depend-on-outer-indvar.ll
@@ -0,0 +1,152 @@
+; RUN: opt < %s -basic-aa -loop-interchange -verify-dom-info -verify-loop-info \
+; RUN: -S -debug 2>&1 | FileCheck %s
+
+ at A = common global [100 x [100 x i64]] zeroinitializer
+ at N = dso_local local_unnamed_addr global i64 100, align 8
+
+
+;; for(int i=0;i<100;i++)
+;; for(int j=0;j<i;j++)
+;; A[j][i] = A[j][i]+k;
+
+;; Inner loop induction variable exit condition depends on the
+;; outer loop induction variable, i.e., triangular loops.
+; CHECK: Loop structure not understood by pass
+; CHECK: Not interchanging loops. Cannot prove legality.
+
+define void @interchange_01(i64 %k) {
+entry:
+ br label %for1.header
+
+for1.header:
+ %i = phi i64 [ 0, %entry ], [ %i.next, %for1.inc10 ]
+ br label %for2
+
+for2:
+ %j = phi i64 [ %j.next, %for2 ], [ 0, %for1.header ]
+ %arrayidx5 = getelementptr inbounds [100 x [100 x i64]], [100 x [100 x i64]]* @A, i64 0, i64 %j, i64 %i
+ %lv = load i64, i64* %arrayidx5
+ %add = add nsw i64 %lv, %k
+ store i64 %add, i64* %arrayidx5
+ %j.next = add nuw nsw i64 %j, 1
+ %exitcond = icmp eq i64 %j, %i
+ br i1 %exitcond, label %for1.inc10, label %for2
+
+for1.inc10:
+ %i.next = add nuw nsw i64 %i, 1
+ %exitcond26 = icmp eq i64 %i, 99
+ br i1 %exitcond26, label %for.end12, label %for1.header
+
+for.end12:
+ ret void
+}
+
+
+;; for(int i=0;i<100;i++)
+;; for(int j=0;j+i<100;j++)
+;; A[j][i] = A[j][i]+k;
+
+;; Inner loop induction variable exit condition depends on the
+;; outer loop induction variable, i.e., triangular loops.
+; CHECK: Loop structure not understood by pass
+; CHECK: Not interchanging loops. Cannot prove legality.
+
+define void @interchange_02(i64 %k) {
+entry:
+ br label %for1.header
+
+for1.header:
+ %i = phi i64 [ 0, %entry ], [ %i.next, %for1.inc10 ]
+ br label %for2
+
+for2:
+ %j = phi i64 [ %j.next, %for2 ], [ 0, %for1.header ]
+ %arrayidx5 = getelementptr inbounds [100 x [100 x i64]], [100 x [100 x i64]]* @A, i64 0, i64 %j, i64 %i
+ %lv = load i64, i64* %arrayidx5
+ %add = add nsw i64 %lv, %k
+ store i64 %add, i64* %arrayidx5
+ %0 = add nuw nsw i64 %j, %i
+ %j.next = add nuw nsw i64 %j, 1
+ %exitcond = icmp eq i64 %0, 100
+ br i1 %exitcond, label %for1.inc10, label %for2
+
+for1.inc10:
+ %i.next = add nuw nsw i64 %i, 1
+ %exitcond26 = icmp eq i64 %i, 99
+ br i1 %exitcond26, label %for.end12, label %for1.header
+
+for.end12:
+ ret void
+}
+
+;; for(int i=0;i<100;i++)
+;; for(int j=0;i>j;j++)
+;; A[j][i] = A[j][i]+k;
+
+;; Inner loop induction variable exit condition depends on the
+;; outer loop induction variable, i.e., triangular loops.
+; CHECK: Loop structure not understood by pass
+; CHECK: Not interchanging loops. Cannot prove legality.
+
+define void @interchange_03(i64 %k) {
+entry:
+ br label %for1.header
+
+for1.header:
+ %i = phi i64 [ 0, %entry ], [ %i.next, %for1.inc10 ]
+ br label %for2
+
+for2:
+ %j = phi i64 [ %j.next, %for2 ], [ 0, %for1.header ]
+ %arrayidx5 = getelementptr inbounds [100 x [100 x i64]], [100 x [100 x i64]]* @A, i64 0, i64 %j, i64 %i
+ %lv = load i64, i64* %arrayidx5
+ %add = add nsw i64 %lv, %k
+ store i64 %add, i64* %arrayidx5
+ %j.next = add nuw nsw i64 %j, 1
+ %exitcond = icmp ne i64 %i, %j
+ br i1 %exitcond, label %for2, label %for1.inc10
+
+for1.inc10:
+ %i.next = add nuw nsw i64 %i, 1
+ %exitcond26 = icmp eq i64 %i, 99
+ br i1 %exitcond26, label %for.end12, label %for1.header
+
+for.end12:
+ ret void
+}
+
+;; for(int i=0;i<100;i++)
+;; for(int j=0;N>j;j++)
+;; A[j][i] = A[j][i]+k;
+
+;; Inner loop induction variable exit condition depends on
+;; an outer loop invariant, can do interchange.
+; CHECK: Loops interchanged
+
+define void @interchange_04(i64 %k) {
+entry:
+ %0 = load i64, i64* @N, align 4
+ br label %for1.header
+
+for1.header:
+ %i = phi i64 [ 0, %entry ], [ %i.next, %for1.inc10 ]
+ br label %for2
+
+for2:
+ %j = phi i64 [ %j.next, %for2 ], [ 0, %for1.header ]
+ %arrayidx5 = getelementptr inbounds [100 x [100 x i64]], [100 x [100 x i64]]* @A, i64 0, i64 %j, i64 %i
+ %lv = load i64, i64* %arrayidx5
+ %add = add nsw i64 %lv, %k
+ store i64 %add, i64* %arrayidx5
+ %j.next = add nuw nsw i64 %j, 1
+ %exitcond = icmp ne i64 %0, %j
+ br i1 %exitcond, label %for2, label %for1.inc10
+
+for1.inc10:
+ %i.next = add nuw nsw i64 %i, 1
+ %exitcond26 = icmp eq i64 %i, 99
+ br i1 %exitcond26, label %for.end12, label %for1.header
+
+for.end12:
+ ret void
+}
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