[polly] Reduction series : [polly] Make reduction detection checks more robust - part 1 (PR #75297)
Karthika Devi C via llvm-commits
llvm-commits at lists.llvm.org
Wed Dec 13 00:14:42 PST 2023
https://github.com/kartcq created https://github.com/llvm/llvm-project/pull/75297
Existing redection detection algorithm does two types of memory checks before marking a load store pair as reduction.
First is to check if load and store are pointing to the same memory.This check right now detects the following case as reduction. sum[0] = sum[1] + A[i]
This is because the check compares only base of the memory addresses involved and not their indices. This patch addresses this issue and introduces some debug prints. Added couple of test cases to verify the functionality of patch as well.
>From 1440d2f96cf981aa90e4cb69c39cde3a81e70c6c Mon Sep 17 00:00:00 2001
From: kartcq <quic_kartc at quicinc.com>
Date: Tue, 12 Dec 2023 01:41:06 -0800
Subject: [PATCH] [polly] Make reduction detection checks more robust - part 1
Existing redection detection algorithm does two types of memory checks
before marking a load store pair as reduction.
First is to check if load and store are pointing to the same memory.This
check right now detects the following case as reduction.
sum[0] = sum[1] + A[i]
This is because the check compares only base of the memory addresses
involved and not their indices. This patch addresses this issue and
introduces some debug prints. Added couple of test cases to verify the
functionality of patch as well.
Change-Id: Ibe523a7d5f1538162f802fb079f32b30ba32175f
---
polly/lib/Analysis/ScopBuilder.cpp | 30 +++++++++++--
.../ScopInfo/reduction_different_index.ll | 38 ++++++++++++++++
.../ScopInfo/reduction_different_index1.ll | 45 +++++++++++++++++++
3 files changed, 110 insertions(+), 3 deletions(-)
create mode 100644 polly/test/ScopInfo/reduction_different_index.ll
create mode 100644 polly/test/ScopInfo/reduction_different_index1.ll
diff --git a/polly/lib/Analysis/ScopBuilder.cpp b/polly/lib/Analysis/ScopBuilder.cpp
index 0af0f6915b145..172f0fa67f29f 100644
--- a/polly/lib/Analysis/ScopBuilder.cpp
+++ b/polly/lib/Analysis/ScopBuilder.cpp
@@ -2536,19 +2536,43 @@ bool hasIntersectingAccesses(isl::set AllAccs, MemoryAccess *LoadMA,
bool checkCandidatePairAccesses(MemoryAccess *LoadMA, MemoryAccess *StoreMA,
isl::set Domain,
SmallVector<MemoryAccess *, 8> &MemAccs) {
+ // First check if the base value is the same.
isl::map LoadAccs = LoadMA->getAccessRelation();
isl::map StoreAccs = StoreMA->getAccessRelation();
-
- // Skip those with obviously unequal base addresses.
bool Valid = LoadAccs.has_equal_space(StoreAccs);
+ LLVM_DEBUG(dbgs() << " == The accessed space below is "
+ << (Valid ? "" : "not ") << "equal!\n");
+ LLVM_DEBUG(LoadMA->dump(); StoreMA->dump());
+
+ if (Valid) {
+ // Then check if they actually access the same memory.
+ isl::map R = isl::manage(LoadAccs.copy())
+ .intersect_domain(isl::manage(Domain.copy()));
+ isl::map W = isl::manage(StoreAccs.copy())
+ .intersect_domain(isl::manage(Domain.copy()));
+ isl::set RS = R.range();
+ isl::set WS = W.range();
+
+ isl::set InterAccs =
+ isl::manage(RS.copy()).intersect(isl::manage(WS.copy()));
+ Valid = !InterAccs.is_empty();
+ LLVM_DEBUG(dbgs() << " == The accessed memory is " << (Valid ? "" : "not ")
+ << "overlapping!\n");
+ }
- // And check if the remaining for overlap with other memory accesses.
if (Valid) {
+ // Finally, check if they are no other instructions accessing this memory
isl::map AllAccsRel = LoadAccs.unite(StoreAccs);
+
AllAccsRel = AllAccsRel.intersect_domain(Domain);
isl::set AllAccs = AllAccsRel.range();
+
Valid = !hasIntersectingAccesses(AllAccs, LoadMA, StoreMA, Domain, MemAccs);
+
+ LLVM_DEBUG(dbgs() << " == The accessed memory is " << (Valid ? "not " : "")
+ << "accessed by other instructions!\n");
}
+
return Valid;
}
diff --git a/polly/test/ScopInfo/reduction_different_index.ll b/polly/test/ScopInfo/reduction_different_index.ll
new file mode 100644
index 0000000000000..575e5a16d7b21
--- /dev/null
+++ b/polly/test/ScopInfo/reduction_different_index.ll
@@ -0,0 +1,38 @@
+; RUN: opt %loadPolly -polly-print-scops -disable-output < %s | FileCheck %s
+; Verify if the following case is not detected as reduction.
+;
+; void f(int *A,int *sum) {
+; for (int i = 0; i < 1024; i++)
+; sum[0] = sum[1] + A[i];
+; }
+;
+; Verify that we don't detect the reduction on sum
+;
+; CHECK: ReadAccess := [Reduction Type: NONE] [Scalar: 0]
+; CHECK-NEXT: { Stmt_for_body[i0] -> MemRef_sum[1] };
+; CHECK-NEXT:ReadAccess := [Reduction Type: NONE] [Scalar: 0]
+; CHECK-NEXT: { Stmt_for_body[i0] -> MemRef_A[i0] };
+; CHECK-NEXT:MustWriteAccess := [Reduction Type: NONE] [Scalar: 0]
+; CHECK-NEXT: { Stmt_for_body[i0] -> MemRef_sum[0] };
+;
+target datalayout = "e-m:e-i8:8:32-i16:16:32-i64:64-i128:128-n32:64-S128"
+
+define dso_local void @f(ptr nocapture noundef readonly %A, ptr nocapture noundef %sum) local_unnamed_addr #0 {
+entry:
+ br label %for.body
+
+for.cond.cleanup: ; preds = %for.body
+ ret void
+
+for.body: ; preds = %entry.split, %for.body
+ %indvars.iv = phi i64 [ 0, %entry ], [ %indvars.iv.next, %for.body ]
+ %arrayidx = getelementptr inbounds i32, ptr %sum, i64 1
+ %0 = load i32, ptr %arrayidx
+ %arrayidx1 = getelementptr inbounds i32, ptr %A, i64 %indvars.iv
+ %1 = load i32, ptr %arrayidx1
+ %add = add nsw i32 %1, %0
+ store i32 %add, ptr %sum
+ %indvars.iv.next = add nuw nsw i64 %indvars.iv, 1
+ %exitcond.not = icmp eq i64 %indvars.iv.next, 1024
+ br i1 %exitcond.not, label %for.cond.cleanup, label %for.body
+}
diff --git a/polly/test/ScopInfo/reduction_different_index1.ll b/polly/test/ScopInfo/reduction_different_index1.ll
new file mode 100644
index 0000000000000..39bd3c4b9abe4
--- /dev/null
+++ b/polly/test/ScopInfo/reduction_different_index1.ll
@@ -0,0 +1,45 @@
+; RUN: opt %loadPolly -polly-print-scops -disable-output < %s | FileCheck %s
+; Verify if the following case is not detected as reduction.
+;
+; void f(int *A, int *sum, int i1, int i2) {
+; for (int i = 0; i < 1024; i++)
+; sum[i2] = sum[i1] + A[i];
+; }
+;
+; Verify that we don't detect the reduction on sum
+;
+; CHECK: ReadAccess := [Reduction Type: NONE] [Scalar: 0]
+; CHECK-NEXT: { Stmt_for_body[i0] -> MemRef_sum[i1] };
+; CHECK-NEXT:ReadAccess := [Reduction Type: NONE] [Scalar: 0]
+; CHECK-NEXT: { Stmt_for_body[i0] -> MemRef_A[i0] };
+; CHECK-NEXT:MustWriteAccess := [Reduction Type: NONE] [Scalar: 0]
+; CHECK-NEXT: { Stmt_for_body[i0] -> MemRef_sum[i2] };
+;
+target datalayout = "e-m:e-i8:8:32-i16:16:32-i64:64-i128:128-n32:64-S128"
+
+; Function Attrs: nofree norecurse nosync nounwind memory(argmem: readwrite) uwtable
+define dso_local void @f(ptr nocapture noundef readonly %A, ptr nocapture noundef %sum, i32 noundef %i1, i32 noundef %i2) local_unnamed_addr #0 {
+entry:
+ br label %entry.split
+
+entry.split: ; preds = %entry
+ %idxprom = sext i32 %i1 to i64
+ %arrayidx = getelementptr inbounds i32, ptr %sum, i64 %idxprom
+ %idxprom3 = sext i32 %i2 to i64
+ %arrayidx4 = getelementptr inbounds i32, ptr %sum, i64 %idxprom3
+ br label %for.body
+
+for.cond.cleanup: ; preds = %for.body
+ ret void
+
+for.body: ; preds = %entry.split, %for.body
+ %indvars.iv = phi i64 [ 0, %entry.split ], [ %indvars.iv.next, %for.body ]
+ %0 = load i32, ptr %arrayidx, align 4
+ %arrayidx2 = getelementptr inbounds i32, ptr %A, i64 %indvars.iv
+ %1 = load i32, ptr %arrayidx2, align 4
+ %add = add nsw i32 %1, %0
+ store i32 %add, ptr %arrayidx4, align 4
+ %indvars.iv.next = add nuw nsw i64 %indvars.iv, 1
+ %exitcond.not = icmp eq i64 %indvars.iv.next, 1024
+ br i1 %exitcond.not, label %for.cond.cleanup, label %for.body
+}
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