[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

@@ -196,6 +196,24 @@ static bool ConvertToSInt(const APFloat &APF, int64_t &IntVal) {
   return true;
 }
 
+// Ensure we stay within the bounds of fp values that can be represented as
+// integers without gaps, namely 2^24 and 2^53 for IEEE-754 single and double
+// precision respectively (both on negative and positive side).
+static bool isRepresentableAsExactInteger(ConstantFP *FPVal, int64_t IntVal) {
+  const auto &InitValueFltSema = FPVal->getValueAPF().getSemantics();
+  if (!APFloat::isIEEELikeFP(InitValueFltSema))
+    return false;
+
+  uint64_t InitValuePrecision = APFloat::semanticsPrecision(InitValueFltSema);
+  if (InitValuePrecision >= 64)
+    return false;
+
+  uint64_t InitValueIntegerLimit = 1LL << InitValuePrecision;
+  if (AbsoluteValue(IntVal) >= InitValueIntegerLimit)
+    return false;
+  return true;
+}
+
 /// If the loop has floating induction variable then insert corresponding
 /// integer induction variable if possible.
 /// For example,
@@ -212,7 +230,8 @@ bool IndVarSimplify::handleFloatingPointIV(Loop *L, PHINode *PN) {
   auto *InitValueVal = dyn_cast<ConstantFP>(PN->getIncomingValue(IncomingEdge));
 
   int64_t InitValue;
-  if (!InitValueVal || !ConvertToSInt(InitValueVal->getValueAPF(), InitValue))
+  if (!InitValueVal || !ConvertToSInt(InitValueVal->getValueAPF(), InitValue) ||
+      !isRepresentableAsExactInteger(InitValueVal, InitValue))
     return false;
 
   // Check IV increment. Reject this PN if increment operation is not
@@ -262,7 +281,8 @@ bool IndVarSimplify::handleFloatingPointIV(Loop *L, PHINode *PN) {
   ConstantFP *ExitValueVal = dyn_cast<ConstantFP>(Compare->getOperand(1));
   int64_t ExitValue;
   if (ExitValueVal == nullptr ||
-      !ConvertToSInt(ExitValueVal->getValueAPF(), ExitValue))
+      !ConvertToSInt(ExitValueVal->getValueAPF(), ExitValue) ||
+      !isRepresentableAsExactInteger(ExitValueVal, ExitValue))
     return false;
 
   // Find new predicate for integer comparison.

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
@@ -505,10 +504,10 @@ define void @test_fp_to_int_irrealizable_exitval_pow_2_24() {
 ; CHECK-NEXT:  entry:
 ; CHECK-NEXT:    br label [[LOOP:%.*]]
 ; CHECK:       loop:
-; CHECK-NEXT:    [[IV_INT:%.*]] = phi i32 [ 0, [[ENTRY:%.*]] ], [ [[IV_NEXT_INT:%.*]], [[LOOP]] ]
+; CHECK-NEXT:    [[IV:%.*]] = phi float [ 0.000000e+00, [[ENTRY:%.*]] ], [ [[IV_NEXT:%.*]], [[LOOP]] ]
 ; CHECK-NEXT:    call void @opaque()
-; CHECK-NEXT:    [[IV_NEXT_INT]] = add nuw nsw i32 [[IV_INT]], 1
-; CHECK-NEXT:    [[CMP:%.*]] = icmp samesign ugt i32 [[IV_NEXT_INT]], 16777216
+; CHECK-NEXT:    [[IV_NEXT]] = fadd float [[IV]], 1.000000e+00
+; CHECK-NEXT:    [[CMP:%.*]] = fcmp ugt float [[IV_NEXT]], 0x4170000000000000
 ; CHECK-NEXT:    br i1 [[CMP]], label [[EXIT:%.*]], label [[LOOP]]
 ; CHECK:       exit:
 ; CHECK-NEXT:    ret void