[llvm] 14d8f15 - [SCEV] Fold (0 udiv %x) to 0

[Philip Reames via llvm-commits]

Author: Philip Reames
Date: 2021-06-30T08:31:13-07:00
New Revision: 14d8f1546a0483ef54a7a09442848d0a470c94c0

URL: https://github.com/llvm/llvm-project/commit/14d8f1546a0483ef54a7a09442848d0a470c94c0
DIFF: https://github.com/llvm/llvm-project/commit/14d8f1546a0483ef54a7a09442848d0a470c94c0.diff

LOG: [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.

Added: 
    

Modified: 
    llvm/lib/Analysis/ScalarEvolution.cpp
    llvm/test/Analysis/ScalarEvolution/fold.ll

Removed: 
    


################################################################################
diff  --git a/llvm/lib/Analysis/ScalarEvolution.cpp b/llvm/lib/Analysis/ScalarEvolution.cpp
index 990f3d6040f4..97ea60f93c54 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 72b62ecaeffc..c23029d521d4 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
 }