[PATCH] D89548: [SCEV] Prove implications of different type via truncation

[Max Kazantsev via Phabricator via llvm-commits]

This revision was automatically updated to reflect the committed changes.
Closed by commit rG5ef84688fba2: Re-enable "[SCEV] Prove implications of different type via truncation" (authored by mkazantsev).

Changed prior to commit:
  https://reviews.llvm.org/D89548?vs=299555&id=301200#toc

Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D89548/new/

https://reviews.llvm.org/D89548

Files:
  llvm/lib/Analysis/ScalarEvolution.cpp
  llvm/test/Analysis/ScalarEvolution/srem.ll
  llvm/unittests/Analysis/ScalarEvolutionTest.cpp


Index: llvm/unittests/Analysis/ScalarEvolutionTest.cpp
===================================================================
--- llvm/unittests/Analysis/ScalarEvolutionTest.cpp
+++ llvm/unittests/Analysis/ScalarEvolutionTest.cpp
@@ -1316,4 +1316,51 @@
   });
 }
 
+TEST_F(ScalarEvolutionsTest, ProveImplicationViaNarrowing) {
+  LLVMContext C;
+  SMDiagnostic Err;
+  std::unique_ptr<Module> M = parseAssemblyString(
+      "define i32 @foo(i32 %start, i32* %q) { "
+      "entry: "
+      "  %wide.start = zext i32 %start to i64 "
+      "  br label %loop "
+      "loop: "
+      "  %wide.iv = phi i64 [%wide.start, %entry], [%wide.iv.next, %backedge] "
+      "  %iv = phi i32 [%start, %entry], [%iv.next, %backedge] "
+      "  %cond = icmp eq i64 %wide.iv, 0 "
+      "  br i1 %cond, label %exit, label %backedge "
+      "backedge: "
+      "  %iv.next = add i32 %iv, -1 "
+      "  %index = zext i32 %iv.next to i64 "
+      "  %load.addr = getelementptr i32, i32* %q, i64 %index "
+      "  %stop = load i32, i32* %load.addr "
+      "  %loop.cond = icmp eq i32 %stop, 0 "
+      "  %wide.iv.next = add nsw i64 %wide.iv, -1 "
+      "  br i1 %loop.cond, label %loop, label %failure "
+      "exit: "
+      "  ret i32 0 "
+      "failure: "
+      "  unreachable "
+      "} ",
+      Err, C);
+
+  ASSERT_TRUE(M && "Could not parse module?");
+  ASSERT_TRUE(!verifyModule(*M) && "Must have been well formed!");
+
+  runWithSE(*M, "foo", [](Function &F, LoopInfo &LI, ScalarEvolution &SE) {
+    auto *IV = SE.getSCEV(getInstructionByName(F, "iv"));
+    auto *Zero = SE.getZero(IV->getType());
+    auto *Backedge = getInstructionByName(F, "iv.next")->getParent();
+    ASSERT_TRUE(Backedge);
+    (void)IV;
+    (void)Zero;
+    // FIXME: This can only be proved with turned on option
+    // scalar-evolution-use-expensive-range-sharpening which is currently off.
+    // Enable the check once it's switched true by default.
+    // EXPECT_TRUE(SE.isBasicBlockEntryGuardedByCond(Backedge,
+    //                                               ICmpInst::ICMP_UGT,
+    //                                               IV, Zero));
+  });
+}
+
 }  // end namespace llvm
Index: llvm/test/Analysis/ScalarEvolution/srem.ll
===================================================================
--- llvm/test/Analysis/ScalarEvolution/srem.ll
+++ llvm/test/Analysis/ScalarEvolution/srem.ll
@@ -29,7 +29,7 @@
 ; CHECK-NEXT:    %add = add nsw i32 %2, %call
 ; CHECK-NEXT:    --> (%2 + %call) U: full-set S: full-set Exits: <<Unknown>> LoopDispositions: { %for.cond: Variant }
 ; CHECK-NEXT:    %inc = add nsw i32 %i.0, 1
-; CHECK-NEXT:    --> {1,+,1}<nuw><%for.cond> U: [1,0) S: [1,0) Exits: (1 + %width) LoopDispositions: { %for.cond: Computable }
+; CHECK-NEXT:    --> {1,+,1}<nuw><%for.cond> U: full-set S: full-set Exits: (1 + %width) LoopDispositions: { %for.cond: Computable }
 ; CHECK-NEXT:  Determining loop execution counts for: @_Z4loopi
 ; CHECK-NEXT:  Loop %for.cond: backedge-taken count is %width
 ; CHECK-NEXT:  Loop %for.cond: max backedge-taken count is -1
Index: llvm/lib/Analysis/ScalarEvolution.cpp
===================================================================
--- llvm/lib/Analysis/ScalarEvolution.cpp
+++ llvm/lib/Analysis/ScalarEvolution.cpp
@@ -9794,6 +9794,25 @@
   // Balance the types.
   if (getTypeSizeInBits(LHS->getType()) <
       getTypeSizeInBits(FoundLHS->getType())) {
+    // For unsigned and equality predicates, try to prove that both found
+    // operands fit into narrow unsigned range. If so, try to prove facts in
+    // narrow types.
+    if (!CmpInst::isSigned(FoundPred)) {
+      auto *NarrowType = LHS->getType();
+      auto *WideType = FoundLHS->getType();
+      auto BitWidth = getTypeSizeInBits(NarrowType);
+      const SCEV *MaxValue = getZeroExtendExpr(
+          getConstant(APInt::getMaxValue(BitWidth)), WideType);
+      if (isKnownPredicate(ICmpInst::ICMP_ULE, FoundLHS, MaxValue) &&
+          isKnownPredicate(ICmpInst::ICMP_ULE, FoundRHS, MaxValue)) {
+        const SCEV *TruncFoundLHS = getTruncateExpr(FoundLHS, NarrowType);
+        const SCEV *TruncFoundRHS = getTruncateExpr(FoundRHS, NarrowType);
+        if (isImpliedCondBalancedTypes(Pred, LHS, RHS, FoundPred, TruncFoundLHS,
+                                       TruncFoundRHS, Context))
+          return true;
+      }
+    }
+
     if (CmpInst::isSigned(Pred)) {
       LHS = getSignExtendExpr(LHS, FoundLHS->getType());
       RHS = getSignExtendExpr(RHS, FoundLHS->getType());


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