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[LoopInterchange] Handle confused dependence correctly (#140709)

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This patch fixes the handling of a confused `Dependence` object. Such an
object doesn’t contain any information about dependencies, so we must
process it conservatively. However, it was converted into a direction
vector like `[I I ... I]`. As a result, it was treated as if there are
no loop-carried dependencies, which can lead to illegal loop exchanges.

Fixes #140238
This commit is contained in:
Ryotaro Kasuga 2025-06-05 16:44:02 +09:00 committed by GitHub
parent 0c89cbb484
commit 1e5f7f64b0
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GPG Key ID: B5690EEEBB952194
4 changed files with 52 additions and 3 deletions
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8
llvm/lib/Transforms/Scalar/LoopInterchange.cpp
View File

@ -209,6 +209,14 @@ static bool populateDependencyMatrix(CharMatrix &DepMatrix, unsigned Level,
Direction = '*';
Dep.push_back(Direction);
}
// If the Dependence object doesn't have any information, fill the
// dependency vector with '*'.
if (D->isConfused()) {
assert(Dep.empty() && "Expected empty dependency vector");
Dep.assign(Level, '*');
}
while (Dep.size() != Level) {
Dep.push_back('I');
}

41
llvm/test/Transforms/LoopInterchange/confused-dependence.ll Normal file
View File

@ -0,0 +1,41 @@
; REQUIRES: asserts
; RUN: opt < %s -passes=loop-interchange -verify-dom-info -verify-loop-info \
; RUN: -disable-output -debug 2>&1 | FileCheck %s
;; In the following case, p0 and p1 may alias, so the direction vector must be [* *].
;;
;; void may_alias(float *p0, float *p1) {
;; for (int i = 0; i < 4; i++)
;; for (int j = 0; j < 4; j++)
;; p0[4 * i + j] = p1[4 * j + i];
;; }
; CHECK: Dependency matrix before interchange:
; CHECK-NEXT: * *
; CHECK-NEXT: Processing InnerLoopId = 1 and OuterLoopId = 0
define void @may_alias(ptr %p0, ptr %p1) {
entry:
br label %for.i.header
for.i.header:
%i = phi i32 [ 0, %entry ], [ %i.inc, %for.i.latch ]
br label %for.j
for.j:
%j = phi i32 [ 0, %for.i.header ], [ %j.inc, %for.j ]
%idx.0 = getelementptr inbounds [4 x [4 x float]], ptr %p0, i32 0, i32 %j, i32 %i
%idx.1 = getelementptr inbounds [4 x [4 x float]], ptr %p1, i32 0, i32 %i, i32 %j
%0 = load float, ptr %idx.0, align 4
store float %0, ptr %idx.1, align 4
%j.inc = add nuw nsw i32 %j, 1
%cmp.j = icmp slt i32 %j.inc, 4
br i1 %cmp.j, label %for.j, label %for.i.latch
for.i.latch:
%i.inc = add nuw nsw i32 %i, 1
%cmp.i = icmp slt i32 %i.inc, 4
br i1 %cmp.i, label %for.i.header, label %exit
exit:
ret void
}

4
llvm/test/Transforms/LoopInterchange/pr43326-ideal-access-pattern.ll
View File

@ -4,7 +4,7 @@
; Triply nested loop, should be able to do interchange three times
; to get the ideal access pattern.
; void f(int e[10][10][10], int f[10][10][10]) {
; void f(int e[restrict 10][10][10], int f[restrict 10][10][10]) {
; for (int a = 0; a < 10; a++) {
; for (int b = 0; b < 10; b++) {
; for (int c = 0; c < 10; c++) {
@ -35,7 +35,7 @@
; REMARKS-NEXT: Name: Interchanged
; REMARKS-NEXT: Function: pr43326-triply-nested
define void @pr43326-triply-nested(ptr %e, ptr %f) {
define void @pr43326-triply-nested(ptr noalias %e, ptr noalias %f) {
entry:
br label %for.outermost.header

2
llvm/test/Transforms/LoopInterchange/unique-dep-matrix.ll
View File

@ -2,7 +2,7 @@
; RUN: opt < %s -passes=loop-interchange -S -debug 2>&1 | FileCheck %s
; CHECK: Dependency matrix before interchange:
; CHECK-NEXT: I I
; CHECK-NEXT: * *
; CHECK-NEXT: = *
; CHECK-NEXT: < *
; CHECK-NEXT: Processing InnerLoopId