From: Philip Reames <listmail@philipreames.com>
Date: Wed, 30 Jun 2021 15:31:13 +0000 (-0700)
Subject: [SCEV] Fold (0 udiv %x) to 0
X-Git-Tag: llvmorg-14-init~2602
X-Git-Url: http://review.tizen.org/git/?a=commitdiff_plain;h=14d8f1546a0483ef54a7a09442848d0a470c94c0;p=platform%2Fupstream%2Fllvm.git

[SCEV] Fold (0 udiv %x) to 0

We have analogous rules in instsimplify, etc.., but were missing the same in SCEV.  The fold is near trivial, but came up in the context of a larger change.
---

diff --git a/llvm/lib/Analysis/ScalarEvolution.cpp b/llvm/lib/Analysis/ScalarEvolution.cpp
index 990f3d6..97ea60f 100644
--- a/llvm/lib/Analysis/ScalarEvolution.cpp
+++ b/llvm/lib/Analysis/ScalarEvolution.cpp
@@ -3268,6 +3268,11 @@ const SCEV *ScalarEvolution::getUDivExpr(const SCEV *LHS,
   if (const SCEV *S = UniqueSCEVs.FindNodeOrInsertPos(ID, IP))
     return S;
 
+  // 0 udiv Y == 0
+  if (const SCEVConstant *LHSC = dyn_cast<SCEVConstant>(LHS))
+    if (LHSC->getValue()->isZero())
+      return LHS;
+
   if (const SCEVConstant *RHSC = dyn_cast<SCEVConstant>(RHS)) {
     if (RHSC->getValue()->isOne())
       return LHS;                               // X udiv 1 --> x
diff --git a/llvm/test/Analysis/ScalarEvolution/fold.ll b/llvm/test/Analysis/ScalarEvolution/fold.ll
index 72b62ec..c23029d 100644
--- a/llvm/test/Analysis/ScalarEvolution/fold.ll
+++ b/llvm/test/Analysis/ScalarEvolution/fold.ll
@@ -132,6 +132,6 @@ define i64 @test11(i64 %a) {
 ; CHECK-LABEL: @test11
   %t0 = udiv i64 0, %a
 ; CHECK: %t0
-; CHECK-NEXT: -->  (0 /u %a)
+; CHECK-NEXT: -->  0
   ret i64 %t0
 }