[IndVarSimplify] Ensure fp values can be represented as consecutive integers

When transforming floating-point induction variables into integer ones,
make sure we stay within the bounds of fp values that can be represented
as integers without gaps, i.e., 2^24 and 2^53 for IEEE-754 single and
double precision respectively (both on negative and positive side).

Fixes: #166496.

Author: antoniofrighetto

llvm/lib/Transforms/Scalar/IndVarSimplify.cpp

@@ -228,6 +228,21 @@ bool IndVarSimplify::handleFloatingPointIV(Loop *L, PHINode *PN) {
       !ConvertToSInt(IncValueVal->getValueAPF(), IncValue))
     return false;
 
+  // Ensure we stay within the bounds of fp values that can be represented
+  // as integers without gaps, i.e., 2^24 and 2^53 for IEEE-754 single and
+  // double precision respectively (both on negative and positive side).
+  const auto &SVFltSema = InitValueVal->getValueAPF().getSemantics();
+  if (!APFloat::isIEEELikeFP(SVFltSema))
+    return false;
+
+  uint64_t StartValPrecision = APFloat::semanticsPrecision(SVFltSema);
+  if (StartValPrecision >= 64)
+    return false;
+
+  uint64_t StartValIntegerLimit = 1LL << StartValPrecision;
+  if (uint64_t(std::abs(InitValue)) > StartValIntegerLimit)
+    return false;
+
   // Check Incr uses. One user is PN and the other user is an exit condition
   // used by the conditional terminator.
   Value::user_iterator IncrUse = Incr->user_begin();
@@ -265,6 +280,18 @@ bool IndVarSimplify::handleFloatingPointIV(Loop *L, PHINode *PN) {
       !ConvertToSInt(ExitValueVal->getValueAPF(), ExitValue))
     return false;
 
+  const auto &EVFltSema = ExitValueVal->getValueAPF().getSemantics();
+  if (!APFloat::isIEEELikeFP(EVFltSema))
+    return false;
+
+  uint64_t ExitValPrecision = APFloat::semanticsPrecision(EVFltSema);
+  if (ExitValPrecision >= 64)
+    return false;
+
+  uint64_t ExitValIntegerLimit = 1LL << ExitValPrecision;
+  if (uint64_t(std::abs(ExitValue)) > ExitValIntegerLimit)
+    return false;
+
   // Find new predicate for integer comparison.
   CmpInst::Predicate NewPred = CmpInst::BAD_ICMP_PREDICATE;
   switch (Compare->getPredicate()) {

llvm/test/Transforms/IndVarSimplify/floating-point-iv.ll

@@ -418,16 +418,15 @@ exit:
   ret void
 }
 
-; FIXME: These are miscompilation issues.
 define void @test_fp_to_int_irrealizable_initval() {
 ; CHECK-LABEL: @test_fp_to_int_irrealizable_initval(
 ; CHECK-NEXT:  entry:
 ; CHECK-NEXT:    br label [[LOOP:%.*]]
 ; CHECK:       loop:
-; CHECK-NEXT:    [[IV_INT:%.*]] = phi i32 [ 100000000, [[ENTRY:%.*]] ], [ [[IV_NEXT_INT:%.*]], [[LOOP]] ]
+; CHECK-NEXT:    [[IV:%.*]] = phi float [ 1.000000e+08, [[ENTRY:%.*]] ], [ [[IV_NEXT:%.*]], [[LOOP]] ]
 ; CHECK-NEXT:    call void @opaque()
-; CHECK-NEXT:    [[IV_NEXT_INT]] = add nsw i32 [[IV_INT]], -17
-; CHECK-NEXT:    [[CMP:%.*]] = icmp samesign ult i32 [[IV_NEXT_INT]], 25
+; CHECK-NEXT:    [[IV_NEXT]] = fadd float [[IV]], -1.700000e+01
+; CHECK-NEXT:    [[CMP:%.*]] = fcmp ult float [[IV_NEXT]], 2.500000e+01
 ; CHECK-NEXT:    br i1 [[CMP]], label [[EXIT:%.*]], label [[LOOP]]
 ; CHECK:       exit:
 ; CHECK-NEXT:    ret void
@@ -451,10 +450,10 @@ define void @test_fp_to_int_irrealizable_exitval() {
 ; CHECK-NEXT:  entry:
 ; CHECK-NEXT:    br label [[LOOP:%.*]]
 ; CHECK:       loop:
-; CHECK-NEXT:    [[IV_INT:%.*]] = phi i32 [ 25, [[ENTRY:%.*]] ], [ [[IV_NEXT_INT:%.*]], [[LOOP]] ]
+; CHECK-NEXT:    [[IV:%.*]] = phi float [ 2.500000e+01, [[ENTRY:%.*]] ], [ [[IV_NEXT:%.*]], [[LOOP]] ]
 ; CHECK-NEXT:    call void @opaque()
-; CHECK-NEXT:    [[IV_NEXT_INT]] = add nuw nsw i32 [[IV_INT]], 17
-; CHECK-NEXT:    [[CMP:%.*]] = icmp samesign ugt i32 [[IV_NEXT_INT]], 100000000
+; CHECK-NEXT:    [[IV_NEXT]] = fadd float [[IV]], 1.700000e+01
+; CHECK-NEXT:    [[CMP:%.*]] = fcmp ugt float [[IV_NEXT]], 1.000000e+08
 ; CHECK-NEXT:    br i1 [[CMP]], label [[EXIT:%.*]], label [[LOOP]]
 ; CHECK:       exit:
 ; CHECK-NEXT:    ret void
@@ -478,10 +477,10 @@ define void @test_fp_to_int_irrealizable_negative_exitval() {
 ; CHECK-NEXT:  entry:
 ; CHECK-NEXT:    br label [[LOOP:%.*]]
 ; CHECK:       loop:
-; CHECK-NEXT:    [[IV_INT:%.*]] = phi i32 [ -25, [[ENTRY:%.*]] ], [ [[IV_NEXT_INT:%.*]], [[LOOP]] ]
+; CHECK-NEXT:    [[IV:%.*]] = phi float [ -2.500000e+01, [[ENTRY:%.*]] ], [ [[IV_NEXT:%.*]], [[LOOP]] ]
 ; CHECK-NEXT:    call void @opaque()
-; CHECK-NEXT:    [[IV_NEXT_INT]] = add nsw i32 [[IV_INT]], -17
-; CHECK-NEXT:    [[CMP:%.*]] = icmp slt i32 [[IV_NEXT_INT]], -100000000
+; CHECK-NEXT:    [[IV_NEXT]] = fadd float [[IV]], -1.700000e+01
+; CHECK-NEXT:    [[CMP:%.*]] = fcmp ult float [[IV_NEXT]], -1.000000e+08
 ; CHECK-NEXT:    br i1 [[CMP]], label [[EXIT:%.*]], label [[LOOP]]
 ; CHECK:       exit:
 ; CHECK-NEXT:    ret void