[IndVars] Support different types of ExitCount when optimizing exit conds

[mkazantsev]

Summary

In some cases we can handle IV and iter count of different types. It's a typical situation
after IV have been widened. This patch adds support for such cases, when legal.

[mkazantsev]

Rebased

[skatkov]

lgtm

llvm/lib/Transforms/Scalar/IndVarSimplify.cpp

if (SE->isKnownPredicateAt(Pred, LHSS, RHSS, BI))
     return CanBeRemoved;
 
   if (ProvingLoopExit)
     return CannotOptimize;
 
   ICmpInst::Predicate InvariantPred;
   const SCEV *InvariantLHS, *InvariantRHS;
 
+  auto *ARTy = LHSS->getType();
+  auto *MaxIterTy = MaxIter->getType();
+  if (ARTy != MaxIterTy) {
+    // If AR's type is wider, just extend the type of max iter.
+    if (SE->getTypeSizeInBits(ARTy) > SE->getTypeSizeInBits(MaxIterTy))
+      MaxIter = SE->getZeroExtendExpr(MaxIter, ARTy);
+    else {
+      const SCEV *MinusOne = SE->getMinusOne(ARTy);
+      auto *MaxAllowedIter = SE->getZeroExtendExpr(MinusOne, MaxIterTy);
+      if (!SE->isKnownPredicateAt(ICmpInst::ICMP_ULE, MaxIter, MaxAllowedIter, BI))
+        return CannotOptimize;
+      MaxIter = SE->getTruncateExpr(MaxIter, ARTy);
+    }
+  }
+
   if (SkipLastIter) {
     const SCEV *One = SE->getOne(MaxIter->getType());
     MaxIter = SE->getMinusSCEV(MaxIter, One);
   }
 
   // Check if there is a loop-invariant predicate equivalent to our check.
   if (!SE->isLoopInvariantExitCondDuringFirstIterations(
            Pred, LHSS, RHSS, L, BI, MaxIter, InvariantPred, InvariantLHS,

llvm/test/Transforms/IndVarSimplify/predicated_ranges.ll

fail:
   unreachable
 }
 
 define void @test_can_predicate_trunc_unsigned(i32* %p, i32* %arr) {
 ; CHECK-LABEL: @test_can_predicate_trunc_unsigned(
 ; CHECK-NEXT:  preheader:
 ; CHECK-NEXT:    [[LEN:%.*]] = load i32, i32* [[P:%.*]], align 4
 ; CHECK-NEXT:    [[START:%.*]] = zext i32 [[LEN]] to i64
+; CHECK-NEXT:    [[TMP0:%.*]] = add i32 [[LEN]], -1
 ; CHECK-NEXT:    br label [[LOOP:%.*]]
 ; CHECK:       loop:
 ; CHECK-NEXT:    [[IV:%.*]] = phi i64 [ [[START]], [[PREHEADER:%.*]] ], [ [[IV_NEXT:%.*]], [[BACKEDGE:%.*]] ]
 ; CHECK-NEXT:    [[ZERO_COND:%.*]] = icmp eq i64 [[IV]], 0
 ; CHECK-NEXT:    br i1 [[ZERO_COND]], label [[EXIT:%.*]], label [[RANGE_CHECK_BLOCK:%.*]]
 ; CHECK:       range_check_block:
 ; CHECK-NEXT:    [[IV_NEXT]] = sub nsw i64 [[IV]], 1
 ; CHECK-NEXT:    [[NARROW:%.*]] = trunc i64 [[IV_NEXT]] to i32
-; CHECK-NEXT:    [[RANGE_CHECK:%.*]] = icmp ult i32 [[NARROW]], [[LEN]]
-; CHECK-NEXT:    br i1 [[RANGE_CHECK]], label [[BACKEDGE]], label [[FAIL:%.*]]
+; CHECK-NEXT:    [[RANGE_CHECK1:%.*]] = icmp ult i32 [[TMP0]], [[LEN]]
+; CHECK-NEXT:    br i1 [[RANGE_CHECK1]], label [[BACKEDGE]], label [[FAIL:%.*]]
 ; CHECK:       backedge:
 ; CHECK-NEXT:    [[EL_PTR:%.*]] = getelementptr i32, i32* [[ARR:%.*]], i64 [[IV]]
 ; CHECK-NEXT:    [[EL:%.*]] = load i32, i32* [[EL_PTR]], align 4
 ; CHECK-NEXT:    [[LOOP_COND:%.*]] = icmp eq i32 [[EL]], 0
 ; CHECK-NEXT:    br i1 [[LOOP_COND]], label [[LOOP]], label [[EXIT]]
 ; CHECK:       exit:
 ; CHECK-NEXT:    ret void
 ; CHECK:       fail: