[llvm] [LoopInterchange] Increment isDirectionNegative check to next level for scalar direction (PR #78951)

[via llvm-commits]

llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-llvm-transforms

Author: None (ShivaChen)

<details>
<summary>Changes</summary>

It could be an alternative way of https://github.com/llvm/llvm-project/pull/77719 to enable interchange for the following case.

    for (int nl = 0; nl < 10000000/256; nl++) // Level 1
      for (int i = 0; i < 256; ++i)                      // Level 2
        for (int j = 1; j < 256; j++)                    // Level 3
          aa[j][i] = aa[j - 1][i] + bb[j][i];

isDirectionNegative() is the function to detect `>` occur and enable normalize ().
It bail out due to the DV for Level 1 is a scalar instead of  `=`.
This commit increments the check to next level as `=` for scalar direction.

---
Full diff: https://github.com/llvm/llvm-project/pull/78951.diff


2 Files Affected:

- (modified) llvm/lib/Analysis/DependenceAnalysis.cpp (+1-1) 
- (added) llvm/test/Transforms/LoopInterchange/pr71519.ll (+64) 


``````````diff
diff --git a/llvm/lib/Analysis/DependenceAnalysis.cpp b/llvm/lib/Analysis/DependenceAnalysis.cpp
index 1bce9aae09bb26..7d25049e03692f 100644
--- a/llvm/lib/Analysis/DependenceAnalysis.cpp
+++ b/llvm/lib/Analysis/DependenceAnalysis.cpp
@@ -290,7 +290,7 @@ FullDependence::FullDependence(Instruction *Source, Instruction *Destination,
 bool FullDependence::isDirectionNegative() const {
   for (unsigned Level = 1; Level <= Levels; ++Level) {
     unsigned char Direction = DV[Level - 1].Direction;
-    if (Direction == Dependence::DVEntry::EQ)
+    if (Direction == Dependence::DVEntry::EQ || isScalar(Level))
       continue;
     if (Direction == Dependence::DVEntry::GT ||
         Direction == Dependence::DVEntry::GE)
diff --git a/llvm/test/Transforms/LoopInterchange/pr71519.ll b/llvm/test/Transforms/LoopInterchange/pr71519.ll
new file mode 100644
index 00000000000000..c364d89873a5dc
--- /dev/null
+++ b/llvm/test/Transforms/LoopInterchange/pr71519.ll
@@ -0,0 +1,64 @@
+; REQUIRES: asserts
+; RUN: opt < %s -passes=loop-interchange -cache-line-size=64 -verify-dom-info -verify-loop-info \
+; RUN:     -S -debug 2>&1 | FileCheck %s
+
+ at aa = global [256 x [256 x float]] zeroinitializer, align 64
+ at bb = global [256 x [256 x float]] zeroinitializer, align 64
+
+;;  for (int nl = 0; nl < 10000000/256; nl++)
+;;    for (int i = 0; i < 256; ++i)
+;;      for (int j = 1; j < 256; j++)
+;;        aa[j][i] = aa[j - 1][i] + bb[j][i];
+
+; CHECK: Before normalizing negative direction vectors:
+; CHECK: consistent anti [S 0 -1]!
+; CHECK: After normalizing negative direction vectors:
+; CHECK: consistent flow [S 0 1]!
+; CHECK: Negative dependence vector normalized.
+; CHECK: Found flow dependency between Src and Dst
+; CHECK:  Src:  %1 = load float, ptr %arrayidx10, align 4
+; CHECK:  Dst:  store float %add, ptr %arrayidx18, align 4
+; CHECK: Processing InnerLoopId = 2 and OuterLoopId = 1
+; CHECK: Loops interchanged.
+
+define float @s231() {
+entry:
+  br label %for.cond1.preheader
+
+; Loop:
+for.cond1.preheader:                              ; preds = %entry, %for.cond.cleanup3
+  %nl.036 = phi i32 [ 0, %entry ], [ %inc23, %for.cond.cleanup3 ]
+  br label %for.cond5.preheader
+
+for.cond.cleanup3:                                ; preds = %for.cond.cleanup7
+  %inc23 = add nuw nsw i32 %nl.036, 1
+  %exitcond41 = icmp ne i32 %inc23, 39062
+  br i1 %exitcond41, label %for.cond1.preheader, label %for.cond.cleanup
+
+for.cond.cleanup7:                                ; preds = %for.body8
+  %indvars.iv.next39 = add nuw nsw i64 %indvars.iv38, 1
+  %exitcond40 = icmp ne i64 %indvars.iv.next39, 256
+  br i1 %exitcond40, label %for.cond5.preheader, label %for.cond.cleanup3
+
+for.body8:                                        ; preds = %for.cond5.preheader, %for.body8
+  %indvars.iv = phi i64 [ 1, %for.cond5.preheader ], [ %indvars.iv.next, %for.body8 ]
+  %0 = add nsw i64 %indvars.iv, -1
+  %arrayidx10 = getelementptr inbounds [256 x [256 x float]], ptr @aa, i64 0, i64 %0, i64 %indvars.iv38
+  %1 = load float, ptr %arrayidx10, align 4
+  %arrayidx14 = getelementptr inbounds [256 x [256 x float]], ptr @bb, i64 0, i64 %indvars.iv, i64 %indvars.iv38
+  %2 = load float, ptr %arrayidx14, align 4
+  %add = fadd fast float %2, %1
+  %arrayidx18 = getelementptr inbounds [256 x [256 x float]], ptr @aa, i64 0, i64 %indvars.iv, i64 %indvars.iv38
+  store float %add, ptr %arrayidx18, align 4
+  %indvars.iv.next = add nuw nsw i64 %indvars.iv, 1
+  %exitcond = icmp ne i64 %indvars.iv.next, 256
+  br i1 %exitcond, label %for.body8, label %for.cond.cleanup7
+
+for.cond5.preheader:                              ; preds = %for.cond1.preheader, %for.cond.cleanup7
+  %indvars.iv38 = phi i64 [ 0, %for.cond1.preheader ], [ %indvars.iv.next39, %for.cond.cleanup7 ]
+  br label %for.body8
+
+; Exit blocks
+for.cond.cleanup:                                 ; preds = %for.cond.cleanup3
+  ret float undef
+}

``````````

</details>


https://github.com/llvm/llvm-project/pull/78951