[PATCH] D87854: [SCEV] Use information from assume for BE taken count.

[Florian Hahn via Phabricator via llvm-commits]

fhahn created this revision.
Herald added a subscriber: hiraditya.
Herald added a project: LLVM.
fhahn requested review of this revision.

Fixes PR47247


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D87854

Files:
  llvm/lib/Analysis/ScalarEvolution.cpp
  llvm/test/Analysis/ScalarEvolution/max-backedge-taken-count-guard-info.ll


Index: llvm/test/Analysis/ScalarEvolution/max-backedge-taken-count-guard-info.ll
===================================================================
--- llvm/test/Analysis/ScalarEvolution/max-backedge-taken-count-guard-info.ll
+++ llvm/test/Analysis/ScalarEvolution/max-backedge-taken-count-guard-info.ll
@@ -30,7 +30,7 @@
 define void @test_guard_and_assume(i32* nocapture readonly %data, i64 %count) {
 ; CHECK-LABEL: Determining loop execution counts for: @test_guard_and_assume
 ; CHECK-NEXT:  Loop %loop: backedge-taken count is (-1 + %count)
-; CHECK-NEXT:  Loop %loop: max backedge-taken count is -2
+; CHECK-NEXT:  Loop %loop: max backedge-taken count is 3
 ; CHECK-NEXT:  Loop %loop: Predicated backedge-taken count is (-1 + %count)
 ;
 entry:
Index: llvm/lib/Analysis/ScalarEvolution.cpp
===================================================================
--- llvm/lib/Analysis/ScalarEvolution.cpp
+++ llvm/lib/Analysis/ScalarEvolution.cpp
@@ -12535,6 +12535,39 @@
 }
 
 const SCEV *ScalarEvolution::applyLoopGuards(const SCEV *Expr, const Loop *L) {
+  auto ApplyCondition = [&](ICmpInst *Cmp) {
+    Value *V = Cmp->getOperand(0);
+    const SCEV *Op0 = getSCEV(Cmp->getOperand(0));
+    const SCEV *Op1 = getSCEV(Cmp->getOperand(1));
+    auto Predicate = Cmp->getPredicate();
+    if (isa<SCEVConstant>(Op0)) {
+      std::swap(Op0, Op1);
+      Predicate = CmpInst::getSwappedPredicate(Predicate);
+      V = Cmp->getOperand(1);
+    }
+    if (!isa<SCEVUnknown>(Op0) || !isa<SCEVConstant>(Op1))
+      return;
+
+    // TODO: use information from more predicates.
+    switch (Predicate) {
+    case CmpInst::ICMP_ULT: {
+      ValueToSCEVMapTy RewriteMap;
+      RewriteMap[V] =
+          getUMinExpr(Op0, getMinusSCEV(Op1, getOne(Op1->getType())));
+      Expr = SCEVParameterRewriter::rewrite(Expr, *this, RewriteMap);
+      break;
+    }
+
+    case CmpInst::ICMP_EQ: {
+      ValueToSCEVMapTy RewriteMap;
+      RewriteMap[V] = getUMaxExpr(Op0, getAddExpr(Op1, getOne(Op1->getType())));
+      Expr = SCEVParameterRewriter::rewrite(Expr, *this, RewriteMap);
+      break;
+    }
+    default:
+      break;
+    }
+  };
   // Starting at the loop predecessor, climb up the predecessor chain, as long
   // as there are predecessors that can be found that have unique successors
   // leading to the original header.
@@ -12553,23 +12586,20 @@
     if (!Cmp)
       continue;
 
-    // TODO: use information from more predicates.
-    switch (Cmp->getPredicate()) {
-    case CmpInst::ICMP_ULT: {
-      const SCEV *LHS = getSCEV(Cmp->getOperand(0));
-      const SCEV *RHS = getSCEV(Cmp->getOperand(1));
-      if (isa<SCEVUnknown>(LHS)) {
-        ValueToSCEVMapTy RewriteMap;
-        RewriteMap[Cmp->getOperand(0)] =
-            getUMinExpr(LHS, getMinusSCEV(RHS, getOne(RHS->getType())));
-        Expr = SCEVParameterRewriter::rewrite(Expr, *this, RewriteMap);
-      }
+    ApplyCondition(Cmp);
+  }
 
-      break;
-    }
-    default:
-      break;
-    }
+  for (auto &AssumeVH : AC.assumptions()) {
+    if (!AssumeVH)
+      continue;
+    auto *CI = cast<CallInst>(AssumeVH);
+    if (!DT.dominates(CI, L->getHeader()))
+      continue;
+    auto *Cmp = dyn_cast<ICmpInst>(CI->getOperand(0));
+    if (!Cmp)
+      continue;
+
+    ApplyCondition(Cmp);
   }
 
   return Expr;


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