[llvm-bugs] [Bug 51623] New: [FastISel] Regression causing miscompile on inline asm

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Wed Aug 25 08:00:46 PDT 2021


            Bug ID: 51623
           Summary: [FastISel] Regression causing miscompile on inline asm
           Product: new-bugs
           Version: trunk
          Hardware: PC
                OS: Linux
            Status: NEW
          Severity: normal
          Priority: P
         Component: new bugs
          Assignee: unassignedbugs at nondot.org
          Reporter: cameron.mcinally at nyu.edu
                CC: chad.rosier at gmail.com, htmldeveloper at gmail.com,
                    llvm-bugs at lists.llvm.org, paul.robinson at am.sony.com,
                    paul_robinson at playstation.sony.com

Created attachment 25193
  --> https://bugs.llvm.org/attachment.cgi?id=25193&action=edit
Reduced test case

The attached test case appears to miscompile after this commit:

> commit c161775decddcc86fbbfefd7485a5d0ef5842aec
> Author: Paul Robinson <Paul.Robinson at sony.com>
> Date: Mon Jan 11 08:32:36 2021 -0800
> [FastISel] Flush local value map on every instruction

This was introduced in the 12.x timeframe, but still occurs in main.

To reproduce:

llc -O0 test.ll

The expected assembly is:

        movl    %eax, %eax
        addl    %ecx, %eax

The current miscompile shows:

        movl    %eax, %ecx
        addl    %ecx, %ecx

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