[llvm] 0074a46 - [LoopInterchange] Hoist isComputableLoopNest() in the control flow (#124247)
via llvm-commits
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Wed Feb 5 00:20:22 PST 2025
Author: Madhur Amilkanthwar
Date: 2025-02-05T13:50:17+05:30
New Revision: 0074a462f1e62ed1df4ac13107043305ba7b8781
URL: https://github.com/llvm/llvm-project/commit/0074a462f1e62ed1df4ac13107043305ba7b8781
DIFF: https://github.com/llvm/llvm-project/commit/0074a462f1e62ed1df4ac13107043305ba7b8781.diff
LOG: [LoopInterchange] Hoist isComputableLoopNest() in the control flow (#124247)
The profiling of the LLVM Test-suite reveals that a significant portion,
specifically 14,090 out of 139,323, loop nests were identified as
non-viable candidates for transformation, leading to the transform
exiting from isComputableLoopNest() without any action.
More importantly, dependence information was computed for these loop
nests before reaching the function isComputableLoopNest(), which does
not require DI and relies solely on scalar evolution (SE).
To enhance compile-time efficiency, this patch moves the call to
isComputableLoopNest() earlier in the control-flow, thereby avoiding
unnecessary dependence calculations.
The impact of this change is evident on the compile-time-tracker, with
the overall geometric mean improvement recorded at 0.11%, while the
lencode benchmark gets a more substantial benefit of 0.44%.
This improvement can be tracked in the isc-ln-exp-2 branch under my
repo.
Added:
llvm/test/Transforms/LoopInterchange/no-dependence-info.ll
Modified:
llvm/lib/Transforms/Scalar/LoopInterchange.cpp
llvm/test/Transforms/LoopInterchange/loop-interchange-optimization-remarks.ll
llvm/test/Transforms/LoopInterchange/pr43326-ideal-access-pattern.ll
llvm/test/Transforms/LoopInterchange/pr43326.ll
llvm/test/Transforms/LoopInterchange/pr48212.ll
llvm/test/Transforms/LoopInterchange/reductions-across-inner-and-outer-loop.ll
Removed:
################################################################################
diff --git a/llvm/lib/Transforms/Scalar/LoopInterchange.cpp b/llvm/lib/Transforms/Scalar/LoopInterchange.cpp
index ca125d2c0c490c..d88fdf41db7a8e 100644
--- a/llvm/lib/Transforms/Scalar/LoopInterchange.cpp
+++ b/llvm/lib/Transforms/Scalar/LoopInterchange.cpp
@@ -276,6 +276,27 @@ static bool hasSupportedLoopDepth(SmallVectorImpl<Loop *> &LoopList,
}
return true;
}
+
+static bool isComputableLoopNest(ScalarEvolution *SE,
+ ArrayRef<Loop *> LoopList) {
+ for (Loop *L : LoopList) {
+ const SCEV *ExitCountOuter = SE->getBackedgeTakenCount(L);
+ if (isa<SCEVCouldNotCompute>(ExitCountOuter)) {
+ LLVM_DEBUG(dbgs() << "Couldn't compute backedge count\n");
+ return false;
+ }
+ if (L->getNumBackEdges() != 1) {
+ LLVM_DEBUG(dbgs() << "NumBackEdges is not equal to 1\n");
+ return false;
+ }
+ if (!L->getExitingBlock()) {
+ LLVM_DEBUG(dbgs() << "Loop doesn't have unique exit block\n");
+ return false;
+ }
+ }
+ return true;
+}
+
namespace {
/// LoopInterchangeLegality checks if it is legal to interchange the loop.
@@ -431,25 +452,6 @@ struct LoopInterchange {
return processLoopList(LoopList);
}
- bool isComputableLoopNest(ArrayRef<Loop *> LoopList) {
- for (Loop *L : LoopList) {
- const SCEV *ExitCountOuter = SE->getBackedgeTakenCount(L);
- if (isa<SCEVCouldNotCompute>(ExitCountOuter)) {
- LLVM_DEBUG(dbgs() << "Couldn't compute backedge count\n");
- return false;
- }
- if (L->getNumBackEdges() != 1) {
- LLVM_DEBUG(dbgs() << "NumBackEdges is not equal to 1\n");
- return false;
- }
- if (!L->getExitingBlock()) {
- LLVM_DEBUG(dbgs() << "Loop doesn't have unique exit block\n");
- return false;
- }
- }
- return true;
- }
-
unsigned selectLoopForInterchange(ArrayRef<Loop *> LoopList) {
// TODO: Add a better heuristic to select the loop to be interchanged based
// on the dependence matrix. Currently we select the innermost loop.
@@ -464,10 +466,6 @@ struct LoopInterchange {
"Unsupported depth of loop nest.");
unsigned LoopNestDepth = LoopList.size();
- if (!isComputableLoopNest(LoopList)) {
- LLVM_DEBUG(dbgs() << "Not valid loop candidate for interchange\n");
- return false;
- }
LLVM_DEBUG(dbgs() << "Processing LoopList of size = " << LoopNestDepth
<< "\n");
@@ -1761,10 +1759,23 @@ PreservedAnalyses LoopInterchangePass::run(LoopNest &LN,
// Ensure minimum depth of the loop nest to do the interchange.
if (!hasSupportedLoopDepth(LoopList, ORE))
return PreservedAnalyses::all();
+ // Ensure computable loop nest.
+ if (!isComputableLoopNest(&AR.SE, LoopList)) {
+ LLVM_DEBUG(dbgs() << "Not valid loop candidate for interchange\n");
+ return PreservedAnalyses::all();
+ }
+
+ ORE.emit([&]() {
+ return OptimizationRemarkAnalysis(DEBUG_TYPE, "Dependence",
+ LN.getOutermostLoop().getStartLoc(),
+ LN.getOutermostLoop().getHeader())
+ << "Computed dependence info, invoking the transform.";
+ });
+
DependenceInfo DI(&F, &AR.AA, &AR.SE, &AR.LI);
std::unique_ptr<CacheCost> CC =
CacheCost::getCacheCost(LN.getOutermostLoop(), AR, DI);
-
+
if (!LoopInterchange(&AR.SE, &AR.LI, &DI, &AR.DT, CC, &ORE).run(LN))
return PreservedAnalyses::all();
U.markLoopNestChanged(true);
diff --git a/llvm/test/Transforms/LoopInterchange/loop-interchange-optimization-remarks.ll b/llvm/test/Transforms/LoopInterchange/loop-interchange-optimization-remarks.ll
index 3c7828a49477c3..73a566a310157d 100644
--- a/llvm/test/Transforms/LoopInterchange/loop-interchange-optimization-remarks.ll
+++ b/llvm/test/Transforms/LoopInterchange/loop-interchange-optimization-remarks.ll
@@ -58,6 +58,14 @@ for.end19:
ret void
}
+; CHECK: --- !Analysis
+; CHECK-NEXT: Pass: loop-interchange
+; CHECK-NEXT: Name: Dependence
+; CHECK-NEXT: Function: test01
+; CHECK-NEXT: Args:
+; CHECK-NEXT: - String: Computed dependence info, invoking the transform.
+; CHECK-NEXT: ...
+
; CHECK: --- !Missed
; CHECK-NEXT: Pass: loop-interchange
; CHECK-NEXT: Name: Dependence
@@ -66,6 +74,14 @@ for.end19:
; CHECK-NEXT: - String: Cannot interchange loops due to dependences.
; CHECK-NEXT: ...
+; DELIN: --- !Analysis
+; DELIN-NEXT: Pass: loop-interchange
+; DELIN-NEXT: Name: Dependence
+; DELIN-NEXT: Function: test01
+; DELIN-NEXT: Args:
+; DELIN-NEXT: - String: Computed dependence info, invoking the transform.
+; DELIN-NEXT: ...
+
; DELIN: --- !Missed
; DELIN-NEXT: Pass: loop-interchange
; DELIN-NEXT: Name: InterchangeNotProfitable
@@ -118,6 +134,14 @@ define void @test02(i32 %k, i32 %N) {
ret void
}
+; CHECK: --- !Analysis
+; CHECK-NEXT: Pass: loop-interchange
+; CHECK-NEXT: Name: Dependence
+; CHECK-NEXT: Function: test02
+; CHECK-NEXT: Args:
+; CHECK-NEXT: - String: Computed dependence info, invoking the transform.
+; CHECK-NEXT: ...
+
; CHECK: --- !Missed
; CHECK-NEXT: Pass: loop-interchange
; CHECK-NEXT: Name: Dependence
@@ -126,6 +150,14 @@ define void @test02(i32 %k, i32 %N) {
; CHECK-NEXT: - String: Cannot interchange loops due to dependences.
; CHECK-NEXT: ...
+; DELIN: --- !Analysis
+; DELIN-NEXT: Pass: loop-interchange
+; DELIN-NEXT: Name: Dependence
+; DELIN-NEXT: Function: test02
+; DELIN-NEXT: Args:
+; DELIN-NEXT: - String: Computed dependence info, invoking the transform.
+; DELIN-NEXT: ...
+
; DELIN: --- !Passed
; DELIN-NEXT: Pass: loop-interchange
; DELIN-NEXT: Name: Interchanged
@@ -174,6 +206,14 @@ for.body4: ; preds = %for.body4, %for.con
br i1 %exitcond, label %for.body4, label %for.cond.loopexit
}
+; CHECK: --- !Analysis
+; CHECK-NEXT: Pass: loop-interchange
+; CHECK-NEXT: Name: Dependence
+; CHECK-NEXT: Function: test03
+; CHECK-NEXT: Args:
+; CHECK-NEXT: - String: Computed dependence info, invoking the transform.
+; CHECK-NEXT: ...
+
; CHECK: --- !Passed
; CHECK-NEXT: Pass: loop-interchange
; CHECK-NEXT: Name: Interchanged
@@ -182,6 +222,14 @@ for.body4: ; preds = %for.body4, %for.con
; CHECK-NEXT: - String: Loop interchanged with enclosing loop.
; CHECK-NEXT: ...
+; DELIN: --- !Analysis
+; DELIN-NEXT: Pass: loop-interchange
+; DELIN-NEXT: Name: Dependence
+; DELIN-NEXT: Function: test03
+; DELIN-NEXT: Args:
+; DELIN-NEXT: - String: Computed dependence info, invoking the transform.
+; DELIN-NEXT: ...
+
; DELIN: --- !Passed
; DELIN-NEXT: Pass: loop-interchange
; DELIN-NEXT: Name: Interchanged
diff --git a/llvm/test/Transforms/LoopInterchange/no-dependence-info.ll b/llvm/test/Transforms/LoopInterchange/no-dependence-info.ll
new file mode 100644
index 00000000000000..d37fb46fc5d68a
--- /dev/null
+++ b/llvm/test/Transforms/LoopInterchange/no-dependence-info.ll
@@ -0,0 +1,52 @@
+; RUN: opt %s -passes='loop-interchange' -pass-remarks=loop-interchange -disable-output 2>&1 | FileCheck --allow-empty %s
+
+target triple = "aarch64-unknown-linux-gnu"
+
+; CHECK-NOT: Computed dependence info, invoking the transform.
+
+; For the below test, backedge count cannot be computed.
+; Computing backedge count requires only SCEV and should
+; not require dependence info.
+;
+; void bar(int m, int n) {
+; for (unsigned int i = 0; i < m; ++i) {
+; for (unsigned int j = 0; j < m; ++j) {
+; // dummy code
+; }
+; }
+;}
+
+define void @bar(i32 %m, i32 %n)
+{
+entry:
+ br label %outer.header
+
+outer.header:
+ %m_temp1 = phi i32 [%m, %entry], [%m_temp, %outer.latch]
+ br label %inner.header
+
+
+inner.header:
+ %n_temp1 = phi i32 [%n, %outer.header], [%n_temp, %inner.latch]
+
+ br label %body
+
+body:
+ ; dummy code
+
+br label %inner.latch
+
+inner.latch:
+%n_temp = add i32 %n_temp1, 1
+%cmp2 = icmp eq i32 %n_temp, 1
+br i1 %cmp2, label %outer.latch, label %inner.header
+
+outer.latch:
+%m_temp = add i32 %n, 1
+%cmp3 = icmp eq i32 %m_temp, 1
+br i1 %cmp3, label %exit, label %outer.header
+
+exit:
+ret void
+}
+
diff --git a/llvm/test/Transforms/LoopInterchange/pr43326-ideal-access-pattern.ll b/llvm/test/Transforms/LoopInterchange/pr43326-ideal-access-pattern.ll
index def68ca3cd07eb..520e1ee3506da8 100644
--- a/llvm/test/Transforms/LoopInterchange/pr43326-ideal-access-pattern.ll
+++ b/llvm/test/Transforms/LoopInterchange/pr43326-ideal-access-pattern.ll
@@ -14,6 +14,14 @@
; }
; }
+; REMARKS: --- !Analysis
+; REMARKS-NEXT: Pass: loop-interchange
+; REMARKS-NEXT: Name: Dependence
+; REMARKS-NEXT: Function: pr43326-triply-nested
+; REMARKS-NEXT: Args:
+; REMARKS-NEXT: - String: Computed dependence info, invoking the transform.
+; REMARKS-NEXT: ...
+
; REMARKS: --- !Passed
; REMARKS-NEXT: Pass: loop-interchange
; REMARKS-NEXT: Name: Interchanged
diff --git a/llvm/test/Transforms/LoopInterchange/pr43326.ll b/llvm/test/Transforms/LoopInterchange/pr43326.ll
index 4dbb06780a8984..c25c4fadd3042d 100644
--- a/llvm/test/Transforms/LoopInterchange/pr43326.ll
+++ b/llvm/test/Transforms/LoopInterchange/pr43326.ll
@@ -8,6 +8,14 @@
@d = global i32 0
@e = global [1 x [1 x i32]] zeroinitializer
+; REMARKS: --- !Analysis
+; REMARKS-NEXT: Pass: loop-interchange
+; REMARKS-NEXT: Name: Dependence
+; REMARKS-NEXT: Function: pr43326
+; REMARKS-NEXT: Args:
+; REMARKS-NEXT: - String: Computed dependence info, invoking the transform.
+; REMARKS-NEXT: ...
+
; REMARKS: --- !Passed
; REMARKS-NEXT: Pass: loop-interchange
; REMARKS-NEXT: Name: Interchanged
diff --git a/llvm/test/Transforms/LoopInterchange/pr48212.ll b/llvm/test/Transforms/LoopInterchange/pr48212.ll
index b580794ab7d36e..936c53e217540e 100644
--- a/llvm/test/Transforms/LoopInterchange/pr48212.ll
+++ b/llvm/test/Transforms/LoopInterchange/pr48212.ll
@@ -2,6 +2,14 @@
; RUN: -verify-dom-info -verify-loop-info -verify-loop-lcssa 2>&1
; RUN: FileCheck --input-file=%t --check-prefix=REMARKS %s
+; REMARKS: --- !Analysis
+; REMARKS-NEXT: Pass: loop-interchange
+; REMARKS-NEXT: Name: Dependence
+; REMARKS-NEXT: Function: pr48212
+; REMARKS-NEXT: Args:
+; REMARKS-NEXT: - String: Computed dependence info, invoking the transform.
+; REMARKS-NEXT: ...
+
; REMARKS: --- !Passed
; REMARKS-NEXT: Pass: loop-interchange
; REMARKS-NEXT: Name: Interchanged
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 eea0c2635d5959..27d99e05e84ee9 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
@@ -5,6 +5,14 @@
target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
+; REMARKS: --- !Analysis
+; REMARKS-NEXT: Pass: loop-interchange
+; REMARKS-NEXT: Name: Dependence
+; REMARKS-NEXT: Function: test1
+; REMARKS-NEXT: Args:
+; REMARKS-NEXT: - String: Computed dependence info, invoking the transform.
+; REMARKS-NEXT: ...
+
; REMARKS: --- !Passed
; REMARKS-NEXT: Pass: loop-interchange
; REMARKS-NEXT: Name: Interchanged
@@ -77,6 +85,14 @@ for1.loopexit: ; preds = %for1.inc
; In this test case, the inner reduction PHI %inner does not involve the outer
; reduction PHI %sum.outer, do not interchange.
+; REMARKS: --- !Analysis
+; REMARKS-NEXT: Pass: loop-interchange
+; REMARKS-NEXT: Name: Dependence
+; REMARKS-NEXT: Function: test2
+; REMARKS-NEXT: Args:
+; REMARKS-NEXT: - String: Computed dependence info, invoking the transform.
+; REMARKS-NEXT: ...
+
; REMARKS: --- !Missed
; REMARKS-NEXT: Pass: loop-interchange
; REMARKS-NEXT: Name: UnsupportedPHIOuter
@@ -114,6 +130,14 @@ for1.loopexit: ; preds = %for1.inc
; Check that we do not interchange if there is an additional instruction
; between the outer and inner reduction PHIs.
+; REMARKS: --- !Analysis
+; REMARKS-NEXT: Pass: loop-interchange
+; REMARKS-NEXT: Name: Dependence
+; REMARKS-NEXT: Function: test3
+; REMARKS-NEXT: Args:
+; REMARKS-NEXT: - String: Computed dependence info, invoking the transform.
+; REMARKS-NEXT: ...
+
; REMARKS: --- !Missed
; REMARKS-NEXT: Pass: loop-interchange
; REMARKS-NEXT: Name: UnsupportedPHIOuter
@@ -151,6 +175,14 @@ for1.loopexit: ; preds = %for1.inc
}
; Check that we do not interchange if reduction is stored in an invariant address inside inner loop
+; REMARKS: --- !Analysis
+; REMARKS-NEXT: Pass: loop-interchange
+; REMARKS-NEXT: Name: Dependence
+; REMARKS-NEXT: Function: test4
+; REMARKS-NEXT: Args:
+; REMARKS-NEXT: - String: Computed dependence info, invoking the transform.
+; REMARKS-NEXT: ...
+
; REMARKS: --- !Missed
; REMARKS-NEXT: Pass: loop-interchange
; REMARKS-NEXT: Name: Dependence
@@ -190,6 +222,14 @@ for1.loopexit: ; preds = %for1.inc
; Check that we do not interchange or crash if the PHI in the outer loop gets a
; constant from the inner loop.
+; REMARKS: --- !Analysis
+; REMARKS-NEXT: Pass: loop-interchange
+; REMARKS-NEXT: Name: Dependence
+; REMARKS-NEXT: Function: test_constant_inner_loop_res
+; REMARKS-NEXT: Args:
+; REMARKS-NEXT: - String: Computed dependence info, invoking the transform.
+; REMARKS-NEXT: ...
+
; REMARKS: --- !Missed
; REMARKS-NEXT: Pass: loop-interchange
; REMARKS-NEXT: Name: UnsupportedPHIOuter
@@ -229,6 +269,14 @@ for1.loopexit: ; preds = %for1.inc
; Floating point reductions are interchanged if all the fp instructions
; involved allow reassociation.
+; REMARKS: --- !Analysis
+; REMARKS-NEXT: Pass: loop-interchange
+; REMARKS-NEXT: Name: Dependence
+; REMARKS-NEXT: Function: test5
+; REMARKS-NEXT: Args:
+; REMARKS-NEXT: - String: Computed dependence info, invoking the transform.
+; REMARKS-NEXT: ...
+
; REMARKS: --- !Passed
; REMARKS-NEXT: Pass: loop-interchange
; REMARKS-NEXT: Name: Interchanged
@@ -269,6 +317,14 @@ for.exit: ; preds = %outer.inc
; Floating point reductions are not interchanged if not all the fp instructions
; involved allow reassociation.
+; REMARKS: --- !Analysis
+; REMARKS-NEXT: Pass: loop-interchange
+; REMARKS-NEXT: Name: Dependence
+; REMARKS-NEXT: Function: test6
+; REMARKS-NEXT: Args:
+; REMARKS-NEXT: - String: Computed dependence info, invoking the transform.
+; REMARKS-NEXT: ...
+
; REMARKS: --- !Missed
; REMARKS-NEXT: Pass: loop-interchange
; REMARKS-NEXT: Name: UnsupportedPHIOuter
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