[DA] Add check for base pointer invariance

[kasuga-fj]

As specified in #53942, DA assumes base pointer invariance in its process. Some cases were fixed by #116628. However, that PR only addressed the parts related to AliasAnalysis, so the original issue persists in later stages, especially when the AliasAnalysis results in MustAlias.
This patch insert an explicit loop-invariant checks for the base pointer and skips analysis when it is not loop-invariant.

Fix the cases added in #148240.

[llvmbot]

@llvm/pr-subscribers-llvm-analysis

Author: Ryotaro Kasuga (kasuga-fj)

Changes

---

Full diff: https://github.com/llvm/llvm-project/pull/148241.diff

2 Files Affected:

• (modified) llvm/lib/Analysis/DependenceAnalysis.cpp (+16)
• (modified) llvm/test/Analysis/DependenceAnalysis/FlipFlopBaseAddress.ll (+9-9)

diff --git a/llvm/lib/Analysis/DependenceAnalysis.cpp b/llvm/lib/Analysis/DependenceAnalysis.cpp
index 428342f51ad2e..07bf560772c8c 100644
--- a/llvm/lib/Analysis/DependenceAnalysis.cpp
+++ b/llvm/lib/Analysis/DependenceAnalysis.cpp
@@ -3383,6 +3383,10 @@ bool DependenceInfo::tryDelinearize(Instruction *Src, Instruction *Dst,
                                     SrcSubscripts, DstSubscripts))
     return false;
 
+  assert(isLoopInvariant(SrcBase, SrcLoop) &&
+         isLoopInvariant(DstBase, DstLoop) &&
+         "Expected SrcBase and DstBase to be loop invariant");
+
   int Size = SrcSubscripts.size();
   LLVM_DEBUG({
     dbgs() << "\nSrcSubscripts: ";
@@ -3666,6 +3670,18 @@ DependenceInfo::depends(Instruction *Src, Instruction *Dst,
                                         SCEVUnionPredicate(Assume, *SE));
   }
 
+  // Even if the base pointers are the same, they may not be loop-invariant. It
+  // could lead to incorrect results, as we're analyzing loop-carried
+  // dependencies.
+  Loop *SrcLoop = LI->getLoopFor(Src->getParent());
+  Loop *DstLoop = LI->getLoopFor(Dst->getParent());
+  if (!isLoopInvariant(SrcBase, SrcLoop) ||
+      !isLoopInvariant(DstBase, DstLoop)) {
+    LLVM_DEBUG(dbgs() << "The base pointer is not loop invariant.\n");
+    return std::make_unique<Dependence>(Src, Dst,
+                                        SCEVUnionPredicate(Assume, *SE));
+  }
+
   uint64_t EltSize = SrcLoc.Size.toRaw();
   const SCEV *SrcEv = SE->getMinusSCEV(SrcSCEV, SrcBase);
   const SCEV *DstEv = SE->getMinusSCEV(DstSCEV, DstBase);
diff --git a/llvm/test/Analysis/DependenceAnalysis/FlipFlopBaseAddress.ll b/llvm/test/Analysis/DependenceAnalysis/FlipFlopBaseAddress.ll
index 843c18a6e0d1e..a357018563be1 100644
--- a/llvm/test/Analysis/DependenceAnalysis/FlipFlopBaseAddress.ll
+++ b/llvm/test/Analysis/DependenceAnalysis/FlipFlopBaseAddress.ll
@@ -8,11 +8,11 @@
 define float @bug41488_test1(float %f) {
 ; CHECK-LABEL: 'bug41488_test1'
 ; CHECK-NEXT:  Src: %0 = load float, ptr %p, align 4 --> Dst: %0 = load float, ptr %p, align 4
-; CHECK-NEXT:    da analyze - input [*]!
+; CHECK-NEXT:    da analyze - confused!
 ; CHECK-NEXT:  Src: %0 = load float, ptr %p, align 4 --> Dst: store float %f, ptr %q, align 4
 ; CHECK-NEXT:    da analyze - confused!
 ; CHECK-NEXT:  Src: store float %f, ptr %q, align 4 --> Dst: store float %f, ptr %q, align 4
-; CHECK-NEXT:    da analyze - output [*]!
+; CHECK-NEXT:    da analyze - confused!
 ;
 entry:
   %g = alloca float, align 4
@@ -34,11 +34,11 @@ for.cond.cleanup:
 define void @bug41488_test2(i32 %n) {
 ; CHECK-LABEL: 'bug41488_test2'
 ; CHECK-NEXT:  Src: %0 = load float, ptr %p, align 4 --> Dst: %0 = load float, ptr %p, align 4
-; CHECK-NEXT:    da analyze - input [*]!
+; CHECK-NEXT:    da analyze - confused!
 ; CHECK-NEXT:  Src: %0 = load float, ptr %p, align 4 --> Dst: store float 0.000000e+00, ptr %q, align 4
 ; CHECK-NEXT:    da analyze - confused!
 ; CHECK-NEXT:  Src: store float 0.000000e+00, ptr %q, align 4 --> Dst: store float 0.000000e+00, ptr %q, align 4
-; CHECK-NEXT:    da analyze - output [*]!
+; CHECK-NEXT:    da analyze - confused!
 ;
 entry:
   %g = alloca float, align 4
@@ -68,7 +68,7 @@ define void @bug53942_foo(i32 noundef %n, ptr noalias nocapture noundef writeonl
 ; CHECK-NEXT:  Src: %.pre = load double, ptr %B, align 8 --> Dst: store double %.pre, ptr %arrayidx2, align 8
 ; CHECK-NEXT:    da analyze - confused!
 ; CHECK-NEXT:  Src: store double %.pre, ptr %arrayidx2, align 8 --> Dst: store double %.pre, ptr %arrayidx2, align 8
-; CHECK-NEXT:    da analyze - output [*]!
+; CHECK-NEXT:    da analyze - confused!
 ;
 entry:
   %cmp8 = icmp sgt i32 %n, 1
@@ -99,11 +99,11 @@ for.body:                                         ; preds = %for.body.preheader,
 define void @bug53942_bar(i32 noundef %n, ptr noalias noundef %A, ptr noalias noundef %B) {
 ; CHECK-LABEL: 'bug53942_bar'
 ; CHECK-NEXT:  Src: %0 = load double, ptr %arrayidx, align 8 --> Dst: %0 = load double, ptr %arrayidx, align 8
-; CHECK-NEXT:    da analyze - input [*]!
+; CHECK-NEXT:    da analyze - confused!
 ; CHECK-NEXT:  Src: %0 = load double, ptr %arrayidx, align 8 --> Dst: store double %0, ptr %arrayidx8, align 8
 ; CHECK-NEXT:    da analyze - confused!
 ; CHECK-NEXT:  Src: store double %0, ptr %arrayidx8, align 8 --> Dst: store double %0, ptr %arrayidx8, align 8
-; CHECK-NEXT:    da analyze - output [*]!
+; CHECK-NEXT:    da analyze - confused!
 ;
 entry:
   br label %for.cond
@@ -173,7 +173,7 @@ for.end:                                          ; preds = %for.cond.cleanup
 define void @non_invariant_baseptr_with_identical_obj(ptr %A) {
 ; CHECK-LABEL: 'non_invariant_baseptr_with_identical_obj'
 ; CHECK-NEXT:  Src: store i32 1, ptr %idx, align 4 --> Dst: store i32 1, ptr %idx, align 4
-; CHECK-NEXT:    da analyze - none!
+; CHECK-NEXT:    da analyze - confused!
 ;
 entry:
   br label %loop.i.header
@@ -222,7 +222,7 @@ exit:
 define void @non_invariant_baseptr_with_identical_underlying_obj2(ptr %A) {
 ; CHECK-LABEL: 'non_invariant_baseptr_with_identical_underlying_obj2'
 ; CHECK-NEXT:  Src: store i32 1, ptr %idx, align 4 --> Dst: store i32 1, ptr %idx, align 4
-; CHECK-NEXT:    da analyze - none!
+; CHECK-NEXT:    da analyze - confused!
 ;
 entry:
   br label %loop.i.header

[kasuga-fj]

All the test changes except for FlipFlopBaseAddress.ll are related to dependencies between memory accesses of the form *B++.