[PATCH] D129710: [SCEVExpander] Allow udiv with isKnownNonZero(RHS) + add vscale case

[Philip Reames via Phabricator via llvm-commits]

This revision was landed with ongoing or failed builds.
This revision was automatically updated to reflect the committed changes.
Closed by commit rG3bc09c7da50a: [SCEVExpander] Allow udiv with isKnownNonZero(RHS) + add vscale case (authored by reames).

Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D129710/new/

https://reviews.llvm.org/D129710

Files:
  llvm/lib/Analysis/ScalarEvolution.cpp
  llvm/lib/Transforms/Utils/ScalarEvolutionExpander.cpp
  llvm/test/Transforms/LoopStrengthReduce/RISCV/icmp-zero.ll


Index: llvm/test/Transforms/LoopStrengthReduce/RISCV/icmp-zero.ll
===================================================================
--- llvm/test/Transforms/LoopStrengthReduce/RISCV/icmp-zero.ll
+++ llvm/test/Transforms/LoopStrengthReduce/RISCV/icmp-zero.ll
@@ -129,10 +129,10 @@
 ; CHECK-NEXT:    [[UREM:%.*]] = urem i64 [[N:%.*]], [[NONZERO]]
 ; CHECK-NEXT:    br label [[VECTOR_BODY:%.*]]
 ; CHECK:       vector.body:
-; CHECK-NEXT:    [[IV:%.*]] = phi i64 [ 0, [[ENTRY:%.*]] ], [ [[IV_NEXT:%.*]], [[VECTOR_BODY]] ]
+; CHECK-NEXT:    [[LSR_IV:%.*]] = phi i64 [ [[LSR_IV_NEXT:%.*]], [[VECTOR_BODY]] ], [ [[UREM]], [[ENTRY:%.*]] ]
 ; CHECK-NEXT:    store i64 0, ptr [[P:%.*]], align 8
-; CHECK-NEXT:    [[IV_NEXT]] = add i64 [[IV]], 2
-; CHECK-NEXT:    [[DONE:%.*]] = icmp eq i64 [[IV_NEXT]], [[UREM]]
+; CHECK-NEXT:    [[LSR_IV_NEXT]] = add i64 [[LSR_IV]], -2
+; CHECK-NEXT:    [[DONE:%.*]] = icmp eq i64 [[LSR_IV_NEXT]], 0
 ; CHECK-NEXT:    br i1 [[DONE]], label [[EXIT:%.*]], label [[VECTOR_BODY]]
 ; CHECK:       exit:
 ; CHECK-NEXT:    ret void
@@ -161,10 +161,10 @@
 ; CHECK-NEXT:    [[UREM:%.*]] = urem i64 [[N:%.*]], [[VSCALE]]
 ; CHECK-NEXT:    br label [[VECTOR_BODY:%.*]]
 ; CHECK:       vector.body:
-; CHECK-NEXT:    [[IV:%.*]] = phi i64 [ 0, [[ENTRY:%.*]] ], [ [[IV_NEXT:%.*]], [[VECTOR_BODY]] ]
+; CHECK-NEXT:    [[LSR_IV:%.*]] = phi i64 [ [[LSR_IV_NEXT:%.*]], [[VECTOR_BODY]] ], [ [[UREM]], [[ENTRY:%.*]] ]
 ; CHECK-NEXT:    store i64 0, ptr [[P:%.*]], align 8
-; CHECK-NEXT:    [[IV_NEXT]] = add i64 [[IV]], 2
-; CHECK-NEXT:    [[DONE:%.*]] = icmp eq i64 [[IV_NEXT]], [[UREM]]
+; CHECK-NEXT:    [[LSR_IV_NEXT]] = add i64 [[LSR_IV]], -2
+; CHECK-NEXT:    [[DONE:%.*]] = icmp eq i64 [[LSR_IV_NEXT]], 0
 ; CHECK-NEXT:    br i1 [[DONE]], label [[EXIT:%.*]], label [[VECTOR_BODY]]
 ; CHECK:       exit:
 ; CHECK-NEXT:    ret void
Index: llvm/lib/Transforms/Utils/ScalarEvolutionExpander.cpp
===================================================================
--- llvm/lib/Transforms/Utils/ScalarEvolutionExpander.cpp
+++ llvm/lib/Transforms/Utils/ScalarEvolutionExpander.cpp
@@ -2572,9 +2572,7 @@
 // only needed when the expression includes some subexpression that is not IV
 // derived.
 //
-// Currently, we only allow division by a nonzero constant here. If this is
-// inadequate, we could easily allow division by SCEVUnknown by using
-// ValueTracking to check isKnownNonZero().
+// Currently, we only allow division by a value provably non-zero here.
 //
 // We cannot generally expand recurrences unless the step dominates the loop
 // header. The expander handles the special case of affine recurrences by
@@ -2592,8 +2590,7 @@
 
   bool follow(const SCEV *S) {
     if (const SCEVUDivExpr *D = dyn_cast<SCEVUDivExpr>(S)) {
-      const SCEVConstant *SC = dyn_cast<SCEVConstant>(D->getRHS());
-      if (!SC || SC->getValue()->isZero()) {
+      if (!SE.isKnownNonZero(D->getRHS())) {
         IsUnsafe = true;
         return false;
       }
Index: llvm/lib/Analysis/ScalarEvolution.cpp
===================================================================
--- llvm/lib/Analysis/ScalarEvolution.cpp
+++ llvm/lib/Analysis/ScalarEvolution.cpp
@@ -6651,6 +6651,13 @@
       }
     }
 
+    // vscale can't be equal to zero
+    if (const auto *II = dyn_cast<IntrinsicInst>(U->getValue()))
+      if (II->getIntrinsicID() == Intrinsic::vscale) {
+        ConstantRange Disallowed = APInt::getZero(BitWidth);
+        ConservativeResult = ConservativeResult.difference(Disallowed);
+      }
+
     return setRange(U, SignHint, std::move(ConservativeResult));
   }
 


-------------- next part --------------
A non-text attachment was scrubbed...
Name: D129710.444687.patch
Type: text/x-patch
Size: 3585 bytes
Desc: not available
URL: <http://lists.llvm.org/pipermail/llvm-commits/attachments/20220714/6441d352/attachment.bin>