[llvm] 456ec1c - [LoopInterchange] Remove 'S' Scalar Dependencies (#119345)
via llvm-commits
llvm-commits at lists.llvm.org
Mon Jan 20 05:05:02 PST 2025
Author: Sjoerd Meijer
Date: 2025-01-20T13:04:58Z
New Revision: 456ec1c2f4e487de235c953e8f2832b97372e7b0
URL: https://github.com/llvm/llvm-project/commit/456ec1c2f4e487de235c953e8f2832b97372e7b0
DIFF: https://github.com/llvm/llvm-project/commit/456ec1c2f4e487de235c953e8f2832b97372e7b0.diff
LOG: [LoopInterchange] Remove 'S' Scalar Dependencies (#119345)
We are not handling 'S' scalar dependencies correctly and have at least
the following miscompiles related to that:
[LoopInterchange] incorrect handling of scalar dependencies and dependence vectors starting with ">" #54176
[LoopInterchange] Interchange breaks program correctness #46867
[LoopInterchange] Loops should not interchanged due to dependencies #47259
[LoopInterchange] Loops should not interchanged due to control flow #47401
This patch does no longer insert the "S" dependency/direction into the
dependency matrix, so a dependency is never "S". We seem to have
forgotten what the exact meaning is of this dependency type, and don't
see why it should be treated differently.
We prefer correctness over incorrect and more aggressive results. I.e.,
this prevents the miscompiles at the expense of handling less cases,
i.e. making interchange more pessimistic. However, some of the cases
that are now rejected for dependence analysis reasons, were rejected
before too but for other reasons (e.g. profitability). So at least for
the llvm regression tests, the number of regression are very reasonable.
This should be a stopgap. We would like to get interchange enabled by
default and thus prefer correctness over unsafe transforms, and later
see if we can get solve the regressions.
Added:
Modified:
llvm/lib/Transforms/Scalar/LoopInterchange.cpp
llvm/test/Transforms/LoopInterchange/gh54176-scalar-deps.ll
llvm/test/Transforms/LoopInterchange/inner-only-reductions.ll
llvm/test/Transforms/LoopInterchange/innermost-latch-uses-values-in-middle-header.ll
llvm/test/Transforms/LoopInterchange/interchange-flow-dep-outer.ll
llvm/test/Transforms/LoopInterchange/lcssa.ll
llvm/test/Transforms/LoopInterchange/outer-header-jump-to-inner-latch.ll
llvm/test/Transforms/LoopInterchange/pr43176-move-to-new-latch.ll
llvm/test/Transforms/LoopInterchange/pr43797-lcssa-for-multiple-outer-loop-blocks.ll
llvm/test/Transforms/LoopInterchange/profitability.ll
llvm/test/Transforms/LoopInterchange/reductions-across-inner-and-outer-loop.ll
llvm/test/Transforms/LoopInterchange/unique-dep-matrix.ll
llvm/test/Transforms/LoopInterchange/vector-gep-operand.ll
Removed:
################################################################################
diff --git a/llvm/lib/Transforms/Scalar/LoopInterchange.cpp b/llvm/lib/Transforms/Scalar/LoopInterchange.cpp
index a0c0080c0bda1c..0d8f52e12d5e4d 100644
--- a/llvm/lib/Transforms/Scalar/LoopInterchange.cpp
+++ b/llvm/lib/Transforms/Scalar/LoopInterchange.cpp
@@ -136,23 +136,17 @@ static bool populateDependencyMatrix(CharMatrix &DepMatrix, unsigned Level,
unsigned Levels = D->getLevels();
char Direction;
for (unsigned II = 1; II <= Levels; ++II) {
- if (D->isScalar(II)) {
- Direction = 'S';
- Dep.push_back(Direction);
- } else {
- unsigned Dir = D->getDirection(II);
- if (Dir == Dependence::DVEntry::LT ||
- Dir == Dependence::DVEntry::LE)
- Direction = '<';
- else if (Dir == Dependence::DVEntry::GT ||
- Dir == Dependence::DVEntry::GE)
- Direction = '>';
- else if (Dir == Dependence::DVEntry::EQ)
- Direction = '=';
- else
- Direction = '*';
- Dep.push_back(Direction);
- }
+ unsigned Dir = D->getDirection(II);
+ if (Dir == Dependence::DVEntry::LT || Dir == Dependence::DVEntry::LE)
+ Direction = '<';
+ else if (Dir == Dependence::DVEntry::GT ||
+ Dir == Dependence::DVEntry::GE)
+ Direction = '>';
+ else if (Dir == Dependence::DVEntry::EQ)
+ Direction = '=';
+ else
+ Direction = '*';
+ Dep.push_back(Direction);
}
while (Dep.size() != Level) {
Dep.push_back('I');
diff --git a/llvm/test/Transforms/LoopInterchange/gh54176-scalar-deps.ll b/llvm/test/Transforms/LoopInterchange/gh54176-scalar-deps.ll
index bc9f16fbe58d6f..6c2f367c2fd2b9 100644
--- a/llvm/test/Transforms/LoopInterchange/gh54176-scalar-deps.ll
+++ b/llvm/test/Transforms/LoopInterchange/gh54176-scalar-deps.ll
@@ -1,3 +1,11 @@
+; Remove 'S' Scalar Dependencies #119345
+; Scalar dependencies are not handled correctly, so they were removed to avoid
+; miscompiles. The loop nest in this test case used to be interchanged, but it's
+; no longer triggering. XFAIL'ing this test to indicate that this test should
+; interchanged if scalar deps are handled correctly.
+;
+; XFAIL: *
+
; RUN: opt < %s -passes=loop-interchange -pass-remarks-output=%t -disable-output
; RUN: FileCheck -input-file %t %s
diff --git a/llvm/test/Transforms/LoopInterchange/inner-only-reductions.ll b/llvm/test/Transforms/LoopInterchange/inner-only-reductions.ll
index 79a1cb71169665..ee1a7f16199288 100644
--- a/llvm/test/Transforms/LoopInterchange/inner-only-reductions.ll
+++ b/llvm/test/Transforms/LoopInterchange/inner-only-reductions.ll
@@ -2,8 +2,11 @@
; RUN: -verify-dom-info -verify-loop-info -verify-loop-lcssa 2>&1 | FileCheck -check-prefix=IR %s
; RUN: FileCheck --input-file=%t %s
-; Inner loop only reductions are not supported currently. See discussion at
-; D53027 for more information on the required checks.
+; Both tests should be rejected as interchange candidates. For now, they are
+; rejected for dependence analysis reasons, but that's because support for 'S'
+; scalar dependencies was removed. When that is properly, the inner loop only
+; reductions should still not be supported currently, see discussion at D53027
+; for more information on the required checks.
@A = common global [500 x [500 x i32]] zeroinitializer
@X = common global i32 0
@@ -18,7 +21,7 @@
; CHECK: --- !Missed
; CHECK-NEXT: Pass: loop-interchange
-; CHECK-NEXT: Name: UnsupportedPHI
+; CHECK-NEXT: Name: Dependence
; CHECK-NEXT: Function: reduction_01
; IR-LABEL: @reduction_01(
@@ -71,7 +74,7 @@ for.end8: ; preds = %for.cond1.for.inc6_
; CHECK: --- !Missed
; CHECK-NEXT: Pass: loop-interchange
-; CHECK-NEXT: Name: UnsupportedPHIOuter
+; CHECK-NEXT: Name: Dependence
; CHECK-NEXT: Function: reduction_03
; IR-LABEL: @reduction_03(
diff --git a/llvm/test/Transforms/LoopInterchange/innermost-latch-uses-values-in-middle-header.ll b/llvm/test/Transforms/LoopInterchange/innermost-latch-uses-values-in-middle-header.ll
index 230f7dc2bcfad9..da37395372e5f5 100644
--- a/llvm/test/Transforms/LoopInterchange/innermost-latch-uses-values-in-middle-header.ll
+++ b/llvm/test/Transforms/LoopInterchange/innermost-latch-uses-values-in-middle-header.ll
@@ -1,3 +1,11 @@
+; Remove 'S' Scalar Dependencies #119345
+; Scalar dependencies are not handled correctly, so they were removed to avoid
+; miscompiles. The loop nest in this test case used to be interchanged, but it's
+; no longer triggering. XFAIL'ing this test to indicate that this test should
+; interchanged if scalar deps are handled correctly.
+;
+; XFAIL: *
+
; RUN: opt < %s -passes=loop-interchange -verify-dom-info -verify-loop-info -pass-remarks-output=%t -disable-output
; RUN: FileCheck -input-file %t %s
diff --git a/llvm/test/Transforms/LoopInterchange/interchange-flow-dep-outer.ll b/llvm/test/Transforms/LoopInterchange/interchange-flow-dep-outer.ll
index a208c1f46a7052..77ab845846bd62 100644
--- a/llvm/test/Transforms/LoopInterchange/interchange-flow-dep-outer.ll
+++ b/llvm/test/Transforms/LoopInterchange/interchange-flow-dep-outer.ll
@@ -1,3 +1,11 @@
+; Remove 'S' Scalar Dependencies #119345
+; Scalar dependencies are not handled correctly, so they were removed to avoid
+; miscompiles. The loop nest in this test case used to be interchanged, but it's
+; no longer triggering. XFAIL'ing this test to indicate that this test should
+; interchanged if scalar deps are handled correctly.
+;
+; XFAIL: *
+
; RUN: opt < %s -passes=loop-interchange -cache-line-size=64 -verify-dom-info -verify-loop-info -pass-remarks-output=%t -disable-output
; RUN: FileCheck -input-file %t %s
diff --git a/llvm/test/Transforms/LoopInterchange/lcssa.ll b/llvm/test/Transforms/LoopInterchange/lcssa.ll
index 0a5aefd9e49111..e77efe3052b40d 100644
--- a/llvm/test/Transforms/LoopInterchange/lcssa.ll
+++ b/llvm/test/Transforms/LoopInterchange/lcssa.ll
@@ -1,3 +1,11 @@
+; Remove 'S' Scalar Dependencies #119345
+; Scalar dependencies are not handled correctly, so they were removed to avoid
+; miscompiles. The loop nest in this test case used to be interchanged, but it's
+; no longer triggering. XFAIL'ing this test to indicate that this test should
+; interchanged if scalar deps are handled correctly.
+;
+; XFAIL: *
+
; RUN: opt < %s -passes=loop-interchange -cache-line-size=64 -pass-remarks-missed='loop-interchange' -verify-loop-lcssa -pass-remarks-output=%t -S
; RUN: FileCheck --input-file %t --check-prefix REMARK %s
@@ -177,7 +185,7 @@ for.end16: ; preds = %for.exit
}
; PHI node in inner latch with multiple predecessors.
-; REMARK: Interchanged
+; REMARK: Interchanged
; REMARK-NEXT: lcssa_05
define void @lcssa_05(ptr %ptr, i1 %arg) {
@@ -222,7 +230,7 @@ for.end16: ; preds = %for.exit
ret void
}
-; REMARK: UnsupportedExitPHI
+; REMARK: UnsupportedExitPHI
; REMARK-NEXT: lcssa_06
define void @lcssa_06(ptr %ptr, ptr %ptr1, i1 %arg) {
diff --git a/llvm/test/Transforms/LoopInterchange/outer-header-jump-to-inner-latch.ll b/llvm/test/Transforms/LoopInterchange/outer-header-jump-to-inner-latch.ll
index aaf8b1daf0414f..5ee1bddbe23fc1 100644
--- a/llvm/test/Transforms/LoopInterchange/outer-header-jump-to-inner-latch.ll
+++ b/llvm/test/Transforms/LoopInterchange/outer-header-jump-to-inner-latch.ll
@@ -1,3 +1,11 @@
+; Remove 'S' Scalar Dependencies #119345
+; Scalar dependencies are not handled correctly, so they were removed to avoid
+; miscompiles. The loop nest in this test case used to be interchanged, but it's
+; no longer triggering. XFAIL'ing this test to indicate that this test should
+; interchanged if scalar deps are handled correctly.
+;
+; XFAIL: *
+
; RUN: opt -passes=loop-interchange -cache-line-size=64 -verify-dom-info -verify-loop-info -verify-loop-lcssa %s -pass-remarks-output=%t -disable-output
; RUN: FileCheck -input-file %t %s
diff --git a/llvm/test/Transforms/LoopInterchange/pr43176-move-to-new-latch.ll b/llvm/test/Transforms/LoopInterchange/pr43176-move-to-new-latch.ll
index 9d2e393937bd5c..6b25c3bc9a4ba1 100644
--- a/llvm/test/Transforms/LoopInterchange/pr43176-move-to-new-latch.ll
+++ b/llvm/test/Transforms/LoopInterchange/pr43176-move-to-new-latch.ll
@@ -14,10 +14,10 @@
; CHECK: --- !Missed
; CHECK-NEXT: Pass: loop-interchange
-; CHECK-NEXT: Name: InterchangeNotProfitable
+; CHECK-NEXT: Name: Dependence
; CHECK-NEXT: Function: test1
; CHECK-NEXT: Args:
-; CHECK-NEXT: - String: Interchanging loops is not considered to improve cache locality nor vectorization.
+; CHECK-NEXT: - String: Cannot interchange loops due to dependences.
define void @test1() {
entry:
@@ -54,10 +54,10 @@ for.cond.for.end5_crit_edge: ; preds = %for.inc3
; CHECK: --- !Missed
; CHECK-NEXT: Pass: loop-interchange
-; CHECK-NEXT: Name: InterchangeNotProfitable
+; CHECK-NEXT: Name: Dependence
; CHECK-NEXT: Function: test2
; CHECK-NEXT: Args:
-; CHECK-NEXT: - String: Interchanging loops is not considered to improve cache locality nor vectorization.
+; CHECK-NEXT: - String: Cannot interchange loops due to dependences.
define void @test2() {
entry:
diff --git a/llvm/test/Transforms/LoopInterchange/pr43797-lcssa-for-multiple-outer-loop-blocks.ll b/llvm/test/Transforms/LoopInterchange/pr43797-lcssa-for-multiple-outer-loop-blocks.ll
index 38970354c3d1ce..51493d72a827d7 100644
--- a/llvm/test/Transforms/LoopInterchange/pr43797-lcssa-for-multiple-outer-loop-blocks.ll
+++ b/llvm/test/Transforms/LoopInterchange/pr43797-lcssa-for-multiple-outer-loop-blocks.ll
@@ -1,3 +1,11 @@
+; Remove 'S' Scalar Dependencies #119345
+; Scalar dependencies are not handled correctly, so they were removed to avoid
+; miscompiles. The loop nest in this test case used to be interchanged, but it's
+; no longer triggering. XFAIL'ing this test to indicate that this test should
+; interchanged if scalar deps are handled correctly.
+;
+; XFAIL: *
+
; RUN: opt -passes=loop-interchange -cache-line-size=64 -verify-loop-lcssa %s -pass-remarks-output=%t -disable-output
; RUN: FileCheck -input-file %t %s
diff --git a/llvm/test/Transforms/LoopInterchange/profitability.ll b/llvm/test/Transforms/LoopInterchange/profitability.ll
index 505c6c422beb6d..4804ecfc8ed6f6 100644
--- a/llvm/test/Transforms/LoopInterchange/profitability.ll
+++ b/llvm/test/Transforms/LoopInterchange/profitability.ll
@@ -1,3 +1,11 @@
+; Remove 'S' Scalar Dependencies #119345
+; Scalar dependencies are not handled correctly, so they were removed to avoid
+; miscompiles. The loop nest in this test case used to be interchanged, but it's
+; no longer triggering. XFAIL'ing this test to indicate that this test should
+; interchanged if scalar deps are handled correctly.
+;
+; XFAIL: *
+
; RUN: opt < %s -passes=loop-interchange -cache-line-size=64 -pass-remarks-output=%t -verify-dom-info -verify-loop-info \
; RUN: -pass-remarks=loop-interchange -pass-remarks-missed=loop-interchange
; RUN: FileCheck -input-file %t %s
diff --git a/llvm/test/Transforms/LoopInterchange/reductions-across-inner-and-outer-loop.ll b/llvm/test/Transforms/LoopInterchange/reductions-across-inner-and-outer-loop.ll
index fa2021a15a0801..eea0c2635d5959 100644
--- a/llvm/test/Transforms/LoopInterchange/reductions-across-inner-and-outer-loop.ll
+++ b/llvm/test/Transforms/LoopInterchange/reductions-across-inner-and-outer-loop.ll
@@ -153,7 +153,7 @@ for1.loopexit: ; preds = %for1.inc
; Check that we do not interchange if reduction is stored in an invariant address inside inner loop
; REMARKS: --- !Missed
; REMARKS-NEXT: Pass: loop-interchange
-; REMARKS-NEXT: Name: UnsupportedPHIOuter
+; REMARKS-NEXT: Name: Dependence
; REMARKS-NEXT: Function: test4
define i64 @test4(ptr %Arr, ptr %dst) {
diff --git a/llvm/test/Transforms/LoopInterchange/unique-dep-matrix.ll b/llvm/test/Transforms/LoopInterchange/unique-dep-matrix.ll
index 6943e39cf163ee..e5c18830784acc 100644
--- a/llvm/test/Transforms/LoopInterchange/unique-dep-matrix.ll
+++ b/llvm/test/Transforms/LoopInterchange/unique-dep-matrix.ll
@@ -3,8 +3,8 @@
; CHECK: Dependency matrix before interchange:
; CHECK-NEXT: I I
-; CHECK-NEXT: = S
-; CHECK-NEXT: < S
+; CHECK-NEXT: = *
+; CHECK-NEXT: < *
; CHECK-NEXT: Processing InnerLoopId
; This example is taken from github issue #54176
diff --git a/llvm/test/Transforms/LoopInterchange/vector-gep-operand.ll b/llvm/test/Transforms/LoopInterchange/vector-gep-operand.ll
index 022cdd44b7f50f..478042f6f3c4df 100644
--- a/llvm/test/Transforms/LoopInterchange/vector-gep-operand.ll
+++ b/llvm/test/Transforms/LoopInterchange/vector-gep-operand.ll
@@ -1,3 +1,11 @@
+; Remove 'S' Scalar Dependencies #119345
+; Scalar dependencies are not handled correctly, so they were removed to avoid
+; miscompiles. The loop nest in this test case used to be interchanged, but it's
+; no longer triggering. XFAIL'ing this test to indicate that this test should
+; interchanged if scalar deps are handled correctly.
+;
+; XFAIL: *
+
; RUN: opt -passes=loop-interchange -cache-line-size=64 -loop-interchange-threshold=-10 %s -pass-remarks-output=%t -disable-output
; RUN: FileCheck -input-file %t %s
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