[LoopCacheAnalysis] Drop incorrect nowrap flags from addrec

[kasuga-fj]

This patch stops propagating nowrap flags unconditionally. In the modified part, when we have an addrec {%a,+,%b} where %b is known to be negative, we create a new addrec {%a,+,(-1 * %b)}. When creating it, the nowrap flags are transferred from the original addrec to the new one without any checks, which is generally incorrect. Since the nowrap property is not essential for this analysis, it would be better to drop it to avoid potential bugs.

[llvmbot]

@llvm/pr-subscribers-llvm-analysis

Author: Ryotaro Kasuga (kasuga-fj)

Changes

This patch stops propagating nowrap flags unconditionally. In the modified part, when we have an addrec {%a,+,%b} where %b is known to be negative, we create a new addrec {%a,+,(-1 * %b)}. In this case, the nowrap flags are transferred from the original addrec to the new one without any checks, which is generally incorrect. Since the nowrap property is not essential for this analysis, it would be better to drop it to avoid potential bugs.

---

Full diff: https://github.com/llvm/llvm-project/pull/164796.diff

1 Files Affected:

• (modified) llvm/lib/Analysis/LoopCacheAnalysis.cpp (+3-4)

diff --git a/llvm/lib/Analysis/LoopCacheAnalysis.cpp b/llvm/lib/Analysis/LoopCacheAnalysis.cpp
index 050c32707596a..424a7fe3721bb 100644
--- a/llvm/lib/Analysis/LoopCacheAnalysis.cpp
+++ b/llvm/lib/Analysis/LoopCacheAnalysis.cpp
@@ -436,10 +436,9 @@ bool IndexedReference::delinearize(const LoopInfo &LI) {
       const SCEV *StepRec = AccessFnAR ? AccessFnAR->getStepRecurrence(SE) : nullptr;
 
       if (StepRec && SE.isKnownNegative(StepRec))
-        AccessFn = SE.getAddRecExpr(AccessFnAR->getStart(),
-                                    SE.getNegativeSCEV(StepRec),
-                                    AccessFnAR->getLoop(),
-                                    AccessFnAR->getNoWrapFlags());
+        AccessFn = SE.getAddRecExpr(
+            AccessFnAR->getStart(), SE.getNegativeSCEV(StepRec),
+            AccessFnAR->getLoop(), SCEV::NoWrapFlags::FlagAnyWrap);
       const SCEV *Div = SE.getUDivExactExpr(AccessFn, ElemSize);
       Subscripts.push_back(Div);
       Sizes.push_back(ElemSize);

[nikic]

LGTM, but this change does not look NFC to me?

[kasuga-fj]

LGTM, but this change does not look NFC to me?

Yes, you're right, this is not NFC. Thanks.