[Float2Int] Fix miscompile with floats that can be converted to large values

There is an issue with Float2Int whenever it has to deal with floats that evaluate to numbers that are over INT_MAX, but under UINT_MAX.

Simply, because the conversion method always assumes a signed integer, this works until the 32 bit number is actually a positive 32 bit number that would be interpreted as a negative number when evaluated as an integer, being put in an i32.

This was messing up the Float2Int conversions and causing miscompiles.

To fix this, tell the APSInt constructor if the value is positive or negative.

Author: AZero13

llvm/lib/Transforms/Scalar/Float2Int.cpp

@@ -407,11 +407,10 @@ Value *Float2IntPass::convert(Instruction *I, Type *ToTy) {
     } else if (Instruction *VI = dyn_cast<Instruction>(V)) {
       NewOperands.push_back(convert(VI, ToTy));
     } else if (ConstantFP *CF = dyn_cast<ConstantFP>(V)) {
-      APSInt Val(ToTy->getPrimitiveSizeInBits(), /*isUnsigned=*/false);
+      const APFloat &F = CF->getValueAPF();
+      APSInt Val(ToTy->getPrimitiveSizeInBits(), !F.isNegative());
       bool Exact;
-      CF->getValueAPF().convertToInteger(Val,
-                                         APFloat::rmNearestTiesToEven,
-                                         &Exact);
+      F.convertToInteger(Val, APFloat::rmNearestTiesToEven, &Exact);
       NewOperands.push_back(ConstantInt::get(ToTy, Val));
     } else {
       llvm_unreachable("Unhandled operand type?");

llvm/test/Transforms/Float2Int/basic.ll

@@ -359,7 +359,7 @@ define i32 @pr79158() {
 ; CHECK-NEXT:    [[X_I_0_X_I_0_X_0_X_0_X_0__I:%.*]] = load volatile i32, ptr [[X_I]], align 4
 ; CHECK-NEXT:    [[CMP_I:%.*]] = icmp sgt i32 [[X_I_0_X_I_0_X_0_X_0_X_0__I]], 0
 ; CHECK-NEXT:    [[TMP0:%.*]] = zext i1 [[CMP_I]] to i32
-; CHECK-NEXT:    [[MUL_I1:%.*]] = mul i32 [[TMP0]], 2147483647
+; CHECK-NEXT:    [[MUL_I1:%.*]] = mul i32 [[TMP0]], -1
 ; CHECK-NEXT:    call void @llvm.lifetime.end.p0(i64 4, ptr nonnull [[X_I]])
 ; CHECK-NEXT:    ret i32 [[MUL_I1]]
 ;
@@ -385,7 +385,7 @@ define i32 @pr79158_2() {
 ; CHECK-NEXT:    [[X_I_0_X_I_0_X_0_X_0_X_0__I:%.*]] = load volatile i32, ptr [[X_I]], align 4
 ; CHECK-NEXT:    [[CMP_I:%.*]] = icmp sgt i32 [[X_I_0_X_I_0_X_0_X_0_X_0__I]], 0
 ; CHECK-NEXT:    [[TMP0:%.*]] = zext i1 [[CMP_I]] to i32
-; CHECK-NEXT:    [[MUL_I1:%.*]] = mul i32 [[TMP0]], 2147483647
+; CHECK-NEXT:    [[MUL_I1:%.*]] = mul i32 [[TMP0]], -2147483648
 ; CHECK-NEXT:    call void @llvm.lifetime.end.p0(i64 4, ptr nonnull [[X_I]])
 ; CHECK-NEXT:    ret i32 [[MUL_I1]]
 ;