Fix constant folding of fp2int to large integers

We make the assumption in most of our constant folding code that a fp2int will target an integer of 128-bits or less, calling the APFloat::convertToInteger with only uint64_t[2] of raw bits for the result.

Fuzz testing (PR24662) showed that we don't handle other cases at all, resulting in stack overflows and all sorts of crashes.

This patch uses the APSInt version of APFloat::convertToInteger instead to better handle such cases.

Differential Revision: https://reviews.llvm.org/D31074

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@298226 91177308-0d34-0410-b5e6-96231b3b80d8

lib/CodeGen/SelectionDAG/FastISel.cpp

@@ -40,7 +40,7 @@
 //===----------------------------------------------------------------------===//
 
 #include "llvm/ADT/APFloat.h"
-#include "llvm/ADT/APInt.h"
+#include "llvm/ADT/APSInt.h"
 #include "llvm/ADT/DenseMap.h"
 #include "llvm/ADT/Optional.h"
 #include "llvm/ADT/SmallPtrSet.h"
@@ -257,17 +257,13 @@ unsigned FastISel::materializeConstant(const Value *V, MVT VT) {
       // Try to emit the constant by using an integer constant with a cast.
       const APFloat &Flt = CF->getValueAPF();
       EVT IntVT = TLI.getPointerTy(DL);
-
-      uint64_t x[2];
       uint32_t IntBitWidth = IntVT.getSizeInBits();
+      APSInt SIntVal(IntBitWidth, /*isUnsigned=*/false);
       bool isExact;
-      (void)Flt.convertToInteger(x, IntBitWidth, /*isSigned=*/true,
-                                 APFloat::rmTowardZero, &isExact);
+      (void)Flt.convertToInteger(SIntVal, APFloat::rmTowardZero, &isExact);
       if (isExact) {
-        APInt IntVal(IntBitWidth, x);
-
         unsigned IntegerReg =
-            getRegForValue(ConstantInt::get(V->getContext(), IntVal));
+            getRegForValue(ConstantInt::get(V->getContext(), SIntVal));
         if (IntegerReg != 0)
           Reg = fastEmit_r(IntVT.getSimpleVT(), VT, ISD::SINT_TO_FP, IntegerReg,
                            /*Kill=*/false);

lib/CodeGen/SelectionDAG/SelectionDAG.cpp

@@ -3434,17 +3434,14 @@ SDValue SelectionDAG::getNode(unsigned Opcode, const SDLoc &DL, EVT VT,
     }
     case ISD::FP_TO_SINT:
     case ISD::FP_TO_UINT: {
-      integerPart x[2];
       bool ignored;
-      static_assert(integerPartWidth >= 64, "APFloat parts too small!");
+      APSInt IntVal(VT.getSizeInBits(), Opcode == ISD::FP_TO_UINT);
       // FIXME need to be more flexible about rounding mode.
-      APFloat::opStatus s = V.convertToInteger(x, VT.getSizeInBits(),
-                            Opcode==ISD::FP_TO_SINT,
-                            APFloat::rmTowardZero, &ignored);
-      if (s==APFloat::opInvalidOp)     // inexact is OK, in fact usual
+      APFloat::opStatus s =
+          V.convertToInteger(IntVal, APFloat::rmTowardZero, &ignored);
+      if (s == APFloat::opInvalidOp) // inexact is OK, in fact usual
         break;
-      APInt api(VT.getSizeInBits(), x);
-      return getConstant(api, DL, VT);
+      return getConstant(IntVal, DL, VT);
     }
     case ISD::BITCAST:
       if (VT == MVT::i16 && C->getValueType(0) == MVT::f16)

lib/IR/ConstantFold.cpp

@@ -18,6 +18,7 @@
 //===----------------------------------------------------------------------===//
 
 #include "ConstantFold.h"
+#include "llvm/ADT/APSInt.h"
 #include "llvm/ADT/SmallVector.h"
 #include "llvm/IR/Constants.h"
 #include "llvm/IR/DerivedTypes.h"
@@ -606,17 +607,15 @@ Constant *llvm::ConstantFoldCastInstruction(unsigned opc, Constant *V,
     if (ConstantFP *FPC = dyn_cast<ConstantFP>(V)) {
       const APFloat &V = FPC->getValueAPF();
       bool ignored;
-      uint64_t x[2];
       uint32_t DestBitWidth = cast<IntegerType>(DestTy)->getBitWidth();
+      APSInt IntVal(DestBitWidth, opc == Instruction::FPToUI);
       if (APFloat::opInvalidOp ==
-          V.convertToInteger(x, DestBitWidth, opc==Instruction::FPToSI,
-                             APFloat::rmTowardZero, &ignored)) {
+          V.convertToInteger(IntVal, APFloat::rmTowardZero, &ignored)) {
         // Undefined behavior invoked - the destination type can't represent
         // the input constant.
         return UndefValue::get(DestTy);
       }
-      APInt Val(DestBitWidth, x);
-      return ConstantInt::get(FPC->getContext(), Val);
+      return ConstantInt::get(FPC->getContext(), IntVal);
     }
     return nullptr; // Can't fold.
   case Instruction::IntToPtr:   //always treated as unsigned

test/CodeGen/Generic/pr24662.ll

@@ -0,0 +1,12 @@
+; RUN: llc < %s -fast-isel
+; RUN: llc < %s
+
+define i60 @PR24662a() {
+  ret i60 trunc (i670010 fptoui(float 0x400D9999A0000000 to i670010) to i60)
+}
+
+define i60 @PR24662b() {
+  %1 = fptoui float 0x400D9999A0000000 to i670010
+  %2 = trunc i670010 %1 to i60
+  ret i60 %2
+}