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Report From: Delphi-BCB/Compiler/Delphi/Code Generation/Optimization [ Add a report in this area ]

Report #: 102926

Status: Closed

Compiler bug, apparently related to the optimiser

Project: Delphi

Build #: 16.0.4358.45540

Version: 16.3

Submitted By: David Heffernan

Report Type: Crash / Data loss / Total failure

Date Reported: 1/26/2012 5:30:20 AM

Severity: Serious / Highly visible problem

Last Updated: 9/5/2012 8:01:50 PM

Platform: All versions

Internal Tracking #: 289659

Resolution: Fixed (Resolution Comments)

Resolved in Build: : 17.0.4625.53395

Duplicate of: None

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Description

The compiler has a rather nasty bug related to parameter passing that is very hard to reproduce. In order to do so I have had to copy the original code in my app and mock the various objects that are used by the mis-behaving routine.

The function in question, when optimisation is enabled, loses track of its self pointer and ends up passing garbage to another procedure.

The bug affects the 32 bit Windows compiler. It does not affect the 64 bit compiler.

Steps to Reproduce:

The attached program illustrates a compiler bug.  The code gen is clearly incorrect.  The code gen is fine when optimisation is switched off, but broken when optimisation is on.  The bug is present in D6 and D2010 also.  I did not test any other versions.  The bug affects the 32 bit Windows compiler.  It does not affect the 64 bit compiler.

The error occurs at this piece of code.  The parameter passing is incorrect because the emitted code uses an incorrect Self pointer.

        Origin3DSeabed := FSeabedOrigin;
        if SpecialDouble(Origin3DSeabed.Z) then begin
          Origin3DSeabed.Z := 0.0; // Ensure that something is drawn even if the depth at the origin is infinite.
        end;
        ViewPort.DrawGeneralSurface(
          Origin3DSeabed,
          FSeabedOrientation,
          GridSize,
          GridSize,
          ViewPort.ScaleBarSize/5.0,
          ViewPort.ScaleBarSize/5.0,
          sdtGrid,
          stGeneral,
          FSeabedPenData,
          [],
          FSeabedPenData,
          CalcSeabedZForRegularlySpacedLine
        );

The (annotated) assembly for this is:

CompilerOptimisationBug.dpr.204: Origin3DSeabed := FSeabedOrigin;
0045DBBA 8B07             mov eax,[edi]  // [edi] is Self
0045DBBC 8D7018           lea esi,[eax+$18]
0045DBBF 8D7DC0           lea edi,[ebp-$40]
0045DBC2 B906000000       mov ecx,$00000006
0045DBC7 F3A5             rep movsd //oops, this modifies edi
........
0045DC39 8B07             mov eax,[edi] //eax is meant to be Self, but is not due to edi having been modified by rep movsd
0045DC3B 8D4830           lea ecx,[eax+$30]
0045DC3E 8D55C0           lea edx,[ebp-$40]
0045DC41 8B4508           mov eax,[ebp+$08]
0045DC44 8B40FC           mov eax,[eax-$04]
0045DC47 E82C020000       call TViewPort.DrawGeneralSurface

I would have added a more complete diagnosis but your QC software limits how much text I can enter!  Please allow me to add more text!

Workarounds

None

Attachment

CompilerOptimisationBug.zip

Comments

None

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