[LoopInterchange] Bail out when finding a dependency with all * elements
#149049
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@llvm/pr-subscribers-llvm-transforms Author: Ryotaro Kasuga (kasuga-fj) ChangesFull diff: https://github.com/llvm/llvm-project/pull/149049.diff 6 Files Affected:
diff --git a/llvm/lib/Transforms/Scalar/LoopInterchange.cpp b/llvm/lib/Transforms/Scalar/LoopInterchange.cpp
index a5008907b9014..68ecf37f90628 100644
--- a/llvm/lib/Transforms/Scalar/LoopInterchange.cpp
+++ b/llvm/lib/Transforms/Scalar/LoopInterchange.cpp
@@ -221,6 +221,18 @@ static bool populateDependencyMatrix(CharMatrix &DepMatrix, unsigned Level,
Dep.push_back('I');
}
+ // If there is a direction vector with all entries being '*', we cannot
+ // prove the legality of the interchange for arbitrary pairs of loops.
+ // Exit early in this case to save compile time.
+ if (all_of(Dep, [](char C) { return C == '*'; })) {
+ ORE->emit([&]() {
+ return OptimizationRemarkMissed(DEBUG_TYPE, "Dependence",
+ L->getStartLoc(), L->getHeader())
+ << "All loops have dependencies in all directions.";
+ });
+ return false;
+ }
+
// Make sure we only add unique entries to the dependency matrix.
if (Seen.insert(StringRef(Dep.data(), Dep.size())).second)
DepMatrix.push_back(Dep);
diff --git a/llvm/test/Transforms/LoopInterchange/bail-out-all-deps.ll b/llvm/test/Transforms/LoopInterchange/bail-out-all-deps.ll
new file mode 100644
index 0000000000000..e22d17e5f5400
--- /dev/null
+++ b/llvm/test/Transforms/LoopInterchange/bail-out-all-deps.ll
@@ -0,0 +1,45 @@
+; RUN: opt < %s -passes=loop-interchange -pass-remarks-output=%t \
+; RUN: -disable-output
+; RUN: FileCheck -input-file %t %s
+
+; Check that loop interchange bail out early when all loops have dependencies
+; in (potentially) all directions.
+;
+; for (int i = 0; i < 4; i++)
+; for (int j = 0; j < 4; j++)
+; A[i & val][j & val] = 42;
+
+; CHECK: --- !Missed
+; CHECK-NEXT: Pass: loop-interchange
+; CHECK-NEXT: Name: Dependence
+; CHECK-NEXT: Function: f
+; CHECK-NEXT: Args:
+; CHECK-NEXT: - String: All loops have dependencies in all directions.
+; CHECK-NEXT: ...
+define void @f(ptr %A, i32 %val) {
+entry:
+ br label %for.i.header
+
+for.i.header:
+ %i = phi i32 [ 0, %entry ], [ %i.next, %for.i.latch ]
+ %subscript.0 = and i32 %i, %val
+ %i2 = mul i32 %i, %i
+ br label %for.j
+
+for.j:
+ %j = phi i32 [ 0, %for.i.header ], [ %j.next, %for.j ]
+ %subscript.1 = and i32 %j, %val
+ %idx = getelementptr inbounds [4 x [4 x i32]], ptr %A, i32 0, i32 %subscript.0, i32 %subscript.1
+ store i32 42, ptr %idx, align 4
+ %j.next = add i32 %j, 1
+ %j.exit = icmp eq i32 %j.next, 4
+ br i1 %j.exit, label %for.i.latch, label %for.j
+
+for.i.latch:
+ %i.next = add i32 %i, 1
+ %i.exit = icmp eq i32 %i.next, 4
+ br i1 %i.exit, label %exit, label %for.i.header
+
+exit:
+ ret void
+}
diff --git a/llvm/test/Transforms/LoopInterchange/confused-dependence.ll b/llvm/test/Transforms/LoopInterchange/confused-dependence.ll
index 49b7b0e4797b8..94080949f0af8 100644
--- a/llvm/test/Transforms/LoopInterchange/confused-dependence.ll
+++ b/llvm/test/Transforms/LoopInterchange/confused-dependence.ll
@@ -1,6 +1,6 @@
-; REQUIRES: asserts
-; RUN: opt < %s -passes=loop-interchange -verify-dom-info -verify-loop-info \
-; RUN: -disable-output -debug 2>&1 | FileCheck %s
+; RUN: opt < %s -passes=loop-interchange -pass-remarks-output=%t \
+; RUN: -disable-output
+; RUN: FileCheck -input-file %t %s
;; In the following case, p0 and p1 may alias, so the direction vector must be [* *].
;;
@@ -10,9 +10,13 @@
;; p0[4 * i + j] = p1[4 * j + i];
;; }
-; CHECK: Dependency matrix before interchange:
-; CHECK-NEXT: * *
-; CHECK-NEXT: Processing InnerLoopId = 1 and OuterLoopId = 0
+; CHECK: --- !Missed
+; CHECK-NEXT: Pass: loop-interchange
+; CHECK-NEXT: Name: Dependence
+; CHECK-NEXT: Function: may_alias
+; CHECK-NEXT: Args:
+; CHECK-NEXT: - String: All loops have dependencies in all directions.
+; CHECK-NEXT: ...
define void @may_alias(ptr %p0, ptr %p1) {
entry:
br label %for.i.header
diff --git a/llvm/test/Transforms/LoopInterchange/legality-for-scalar-deps.ll b/llvm/test/Transforms/LoopInterchange/legality-for-scalar-deps.ll
index c30f9a399fed8..5f4a8486d9ad7 100644
--- a/llvm/test/Transforms/LoopInterchange/legality-for-scalar-deps.ll
+++ b/llvm/test/Transforms/LoopInterchange/legality-for-scalar-deps.ll
@@ -21,13 +21,13 @@
; CHECK-NEXT: Name: Dependence
; CHECK-NEXT: Function: issue46867
; CHECK-NEXT: Args:
-; CHECK-NEXT: - String: Cannot interchange loops due to dependences.
+; CHECK-NEXT: - String: All loops have dependencies in all directions.
; CHECK: --- !Missed
; CHECK-NEXT: Pass: loop-interchange
; CHECK-NEXT: Name: Dependence
; CHECK-NEXT: Function: issue46867
; CHECK-NEXT: Args:
-; CHECK-NEXT: - String: Cannot interchange loops due to dependences.
+; CHECK-NEXT: - String: All loops have dependencies in all directions.
define void @issue46867(ptr noundef captures(none) %s, i32 noundef %c, ptr noundef readonly captures(none) %ff) {
entry:
%tobool7.not = icmp eq i32 %c, 0
@@ -121,7 +121,7 @@ land.end:
; CHECK-NEXT: Name: Dependence
; CHECK-NEXT: Function: issue47401
; CHECK-NEXT: Args:
-; CHECK-NEXT: - String: Cannot interchange loops due to dependences.
+; CHECK-NEXT: - String: All loops have dependencies in all directions.
define void @issue47401(ptr noundef writeonly captures(none) %e, ptr noundef readonly captures(none) %bb) {
entry:
br label %for.cond1.preheader
@@ -175,7 +175,7 @@ land.end:
; CHECK-NEXT: Name: Dependence
; CHECK-NEXT: Function: issue47295
; CHECK-NEXT: Args:
-; CHECK-NEXT: - String: Cannot interchange loops due to dependences.
+; CHECK-NEXT: - String: All loops have dependencies in all directions.
define void @issue47295(ptr noundef captures(none) %f, ptr noundef writeonly captures(none) %cc) {
entry:
br label %for.cond1.preheader
@@ -221,7 +221,7 @@ for.body4:
; CHECK-NEXT: Name: Dependence
; CHECK-NEXT: Function: issue54176
; CHECK-NEXT: Args:
-; CHECK-NEXT: - String: Cannot interchange loops due to dependences.
+; CHECK-NEXT: - String: All loops have dependencies in all directions.
define void @issue54176(i32 noundef %n, i32 noundef %m, ptr noundef captures(none) %aa, ptr noundef readonly captures(none) %bb, ptr noundef writeonly captures(none) %cc) {
entry:
diff --git a/llvm/test/Transforms/LoopInterchange/loop-interchange-optimization-remarks.ll b/llvm/test/Transforms/LoopInterchange/loop-interchange-optimization-remarks.ll
index 73a566a310157..14836ba73433d 100644
--- a/llvm/test/Transforms/LoopInterchange/loop-interchange-optimization-remarks.ll
+++ b/llvm/test/Transforms/LoopInterchange/loop-interchange-optimization-remarks.ll
@@ -71,7 +71,7 @@ for.end19:
; CHECK-NEXT: Name: Dependence
; CHECK-NEXT: Function: test01
; CHECK-NEXT: Args:
-; CHECK-NEXT: - String: Cannot interchange loops due to dependences.
+; CHECK-NEXT: - String: All loops have dependencies in all directions.
; CHECK-NEXT: ...
; DELIN: --- !Analysis
@@ -147,7 +147,7 @@ define void @test02(i32 %k, i32 %N) {
; CHECK-NEXT: Name: Dependence
; CHECK-NEXT: Function: test02
; CHECK-NEXT: Args:
-; CHECK-NEXT: - String: Cannot interchange loops due to dependences.
+; CHECK-NEXT: - String: All loops have dependencies in all directions.
; CHECK-NEXT: ...
; DELIN: --- !Analysis
@@ -290,7 +290,7 @@ for.end17:
; CHECK-NEXT: Name: Dependence
; CHECK-NEXT: Function: test04
; CHECK-NEXT: Args:
-; CHECK-NEXT: - String: Cannot interchange loops due to dependences.
+; CHECK-NEXT: - String: All loops have dependencies in all directions.
; CHECK-NEXT: ...
; DELIN: --- !Missed
diff --git a/llvm/test/Transforms/LoopInterchange/unique-dep-matrix.ll b/llvm/test/Transforms/LoopInterchange/unique-dep-matrix.ll
index 68089b43121c5..3af9e7304e3be 100644
--- a/llvm/test/Transforms/LoopInterchange/unique-dep-matrix.ll
+++ b/llvm/test/Transforms/LoopInterchange/unique-dep-matrix.ll
@@ -2,14 +2,13 @@
; RUN: opt < %s -passes=loop-interchange -S -debug 2>&1 | FileCheck %s
; CHECK: Dependency matrix before interchange:
-; CHECK-NEXT: * *
; CHECK-NEXT: = *
; CHECK-NEXT: < *
; CHECK-NEXT: Processing InnerLoopId
; This example is taken from github issue #54176
;
-define void @foo(i32 noundef %n, i32 noundef %m, ptr nocapture noundef %aa, ptr nocapture noundef readonly %bb, ptr nocapture noundef writeonly %cc) {
+define void @foo(i32 noundef %n, i32 noundef %m, ptr nocapture noundef noalias %aa, ptr nocapture noundef readonly noalias %bb, ptr nocapture noundef writeonly noalias %cc) {
entry:
%arrayidx7 = getelementptr inbounds i8, ptr %aa, i64 512
br label %for.cond1.preheader
|
kasuga-fj
commented
Jul 16, 2025
Comment on lines
-13
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| ; CHECK: Dependency matrix before interchange: | ||
| ; CHECK-NEXT: * * | ||
| ; CHECK-NEXT: Processing InnerLoopId = 1 and OuterLoopId = 0 | ||
| ; CHECK: --- !Missed | ||
| ; CHECK-NEXT: Pass: loop-interchange | ||
| ; CHECK-NEXT: Name: Dependence | ||
| ; CHECK-NEXT: Function: may_alias | ||
| ; CHECK-NEXT: Args: | ||
| ; CHECK-NEXT: - String: All loops have dependencies in all directions. | ||
| ; CHECK-NEXT: ... |
There was a problem hiding this comment.
Changed because the previous CHECK directives check the debug outputs, which are no longer printed due to this change.
Comment on lines
-5
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+11
| ; CHECK-NEXT: * * | ||
| ; CHECK-NEXT: = * | ||
| ; CHECK-NEXT: < * | ||
| ; CHECK-NEXT: Processing InnerLoopId | ||
|
|
||
| ; This example is taken from github issue #54176 | ||
| ; | ||
| define void @foo(i32 noundef %n, i32 noundef %m, ptr nocapture noundef %aa, ptr nocapture noundef readonly %bb, ptr nocapture noundef writeonly %cc) { | ||
| define void @foo(i32 noundef %n, i32 noundef %m, ptr nocapture noundef noalias %aa, ptr nocapture noundef readonly noalias %bb, ptr nocapture noundef writeonly noalias %cc) { |
There was a problem hiding this comment.
Added noalias to all ptr arguments to eliminate the * * dependency.
|
Ping |
kasuga-fj
changed the title
* elements
madhur13490
reviewed
Sep 25, 2025
| // If there is a direction vector with all entries being '*', we cannot | ||
| // prove the legality of the interchange for arbitrary pairs of loops. | ||
| // Exit early in this case to save compile time. | ||
| if (all_of(Dep, [](char C) { return C == '*'; })) { |
There was a problem hiding this comment.
Can be reworded to the following for clarity.
// If all the elements of any direction vector have only '*', legality can't be proven.
// Exit early to save compile time.
madhur13490
reviewed
Sep 25, 2025
madhur13490
approved these changes
Sep 25, 2025
ckoparkar
added a commit
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that referenced
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Sep 25, 2025
* main: (502 commits) GlobalISel: Adjust insert point when expanding G_[SU]DIVREM (llvm#160683) [LV] Add coverage for fixing-up scalar resume values (llvm#160492) AMDGPU: Convert wave_any test to use update_mc_test_checks [LV] Add partial reduction tests multiplying extend with constants. Revert "[MLIR] Implement remark emitting policies in MLIR" (llvm#160681) [NFC][InstSimplify] Refactor fminmax-folds.ll test (llvm#160504) [LoongArch] Pre-commit tests for [x]vldi instructions with special constant splats (llvm#159228) [BOLT] Fix dwarf5-dwoid-no-dwoname.s (llvm#160676) [lldb][test] Refactor and expand TestMemoryRegionDirtyPages.py (llvm#156035) [gn build] Port 833d5f0 AMDGPU: Ensure both wavesize features are not set (llvm#159234) [LoopInterchange] Bail out when finding a dependency with all `*` elements (llvm#149049) [libc++] Avoid constructing additional objects when using map::at (llvm#157866) [lldb][test] Make hex prefix optional in DWARF union types test [X86] Add missing prefixes to trunc-sat tests (llvm#160662) [AMDGPU] Fix vector legalization for bf16 valu ops (llvm#158439) [LoongArch][NFC] Pre-commit tests for `[x]vadda.{b/h/w/d}` [mlir][tosa] Relax constraint on matmul verifier requiring equal operand types (llvm#155799) [clang][Sema] Accept gnu format attributes (llvm#160255) [LoongArch][NFC] Add tests for element extraction from binary add operation (llvm#159725) ...
mahesh-attarde
pushed a commit
to mahesh-attarde/llvm-project
that referenced
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Oct 3, 2025
…ments (llvm#149049) If a direction vector with all `*` elements, like `[* * *]`, is present, it indicates that none of the loop pairs are legal to interchange. In such cases, continuing the analysis is meaningless. This patch introduces a check to detect such direction vectors and exits early when one is found. This slightly reduces compile time.
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If a direction vector with all
*elements, like[* * *], is present, it indicates that none of the loop pairs are legal to interchange. In such cases, continuing the analysis is meaningless.This patch introduces a check to detect such direction vectors and exits early when one is found. This slightly reduces compile time.