Wrong result of inlined function

Summary

A function containing a specific mathematical calculation returns an incorrect result when the function is inlined.

System Information

  • Operating system: Linux Mint 21.1 (no issue on Windows)
  • Processor architecture: x86-64
  • Compiler version: FPC 3.3.1 commit 2584b5c175fdfb3eb7476304f34a68005a307eaa (I did not observe the issue on FPC 3.2.2)
  • Device: Computer

Steps to reproduce

Run the project shown below. In the function Calc, it calculates the value of Power(10, Floor(Log10(0.01))).

The appearance of this issue does not depend on the exact values of the literal numbers used. There are some combinations, though, where the inlined function returns the correct result (e.g. using 1.0 in the Log10).

Example Project 

program project1;
uses
  Math;

function Calc: Double; inline;
begin
  Result := Power(10, Floor(Log10(0.01)));
end;

begin
  WriteLn(Calc:0:3);
end.

What is the current bug behavior?

The return value of the function Calc is wrong, when it is declared as inline. The output of the test project is 0.250 while it should be 0.010.

The appearance of this issue usually does not depend on the exact values of the literal numbers used. There are some combinations, though, where the inlined function returns the correct result (e.g. using 1.0 in the Log10).

What is the expected (correct) behavior?

The correct result can be calculated directly: log10(0.01) = -2, Floor(-2) = -2, Power(10,-2) = 10^-2 = 0.01. This result is obtained when the inline is removed from the function declaration.

Notes

  • The issue does not appear on Windows, I saw it only on Linux.
  • The issue is tied to FPC/main, the release version does not have it. (did not test FIXES).
Edited by Werner Pamler