Consider the following program: ```pascal var A, B, C: QWord; begin A := 140737488355327; WriteLn('A : ',BinStr(A, 64)); B := (A shr 47) shl 48; WriteLn('(A shr 47) shl 48: ',BinStr(B, 64)); C := A shr 47; writeln('C := A shr 47 : ',BinStr(C, 64)); C := C shl 48; WriteLn('C := C shl 48 : ',BinStr(C, 64)); end. ``` The 2 calculations should give the same result. If you build for Win64 and use -O1 or higher the output will be wrong: ``` C:\Users\Bart\LazarusProjecten\bugs\Console\bitshift>fpc test.lpr -Px86_64 -O1 Free Pascal Compiler version 3.3.1 [2024/12/18] for x86_64 Copyright (c) 1993-2024 by Florian Klaempfl and others Target OS: Win64 for x64 Compiling test.lpr Linking test.exe 17 lines compiled, 0.1 sec, 33872 bytes code, 1732 bytes data C:\Users\Bart\LazarusProjecten\bugs\Console\bitshift>test A : 0000000000000000011111111111111111111111111111111111111111111111 (A shr 47) shl 48: 0000000000000000111111111111111111111111111111110000000000000000 C := A shr 47 : 0000000000000000000000000000000000000000000000000000000000000000 C := C shl 48 : 0000000000000000000000000000000000000000000000000000000000000000 ``` You get the correct output with -O-, or compiling for 32-bit (with any value for -O): ``` C:\Users\Bart\LazarusProjecten\bugs\Console\bitshift>fpc test.lpr -Px86_64 Free Pascal Compiler version 3.3.1 [2024/12/18] for x86_64 Copyright (c) 1993-2024 by Florian Klaempfl and others Target OS: Win64 for x64 Compiling test.lpr Linking test.exe 17 lines compiled, 0.1 sec, 33920 bytes code, 1732 bytes data C:\Users\Bart\LazarusProjecten\bugs\Console\bitshift>test A : 0000000000000000011111111111111111111111111111111111111111111111 (A shr 47) shl 48: 0000000000000000000000000000000000000000000000000000000000000000 C := A shr 47 : 0000000000000000000000000000000000000000000000000000000000000000 C := C shl 48 : 0000000000000000000000000000000000000000000000000000000000000000 ``` The error does not seem to depend on the state of range-checking or overflow-checking. Issue originally raised in [the forum](https://forum.lazarus.freepascal.org/index.php/topic,69714.msg541970.html#msg541970). Tested with fpc main (3.3.1-5463-gb28681e91d). (The issue is also present in fpc 3.2.2 and 3.2.0, but not on 3.0.4)