https://bugs.llvm.org/show_bug.cgi?id=50615
Bug ID: 50615
Summary: Miscompile with "[X86FixupLEAs] Transform the sequence
LEA/SUB to SUB/SUB"
Product: new-bugs
Version: trunk
Hardware: PC
OS: Windows NT
Status: NEW
Severity: enhancement
Priority: P
Component: new bugs
Assignee: unassignedb...@nondot.org
Reporter: max.kazant...@azul.com
CC: htmldevelo...@gmail.com, llvm-bugs@lists.llvm.org
Created attachment 24925
--> https://bugs.llvm.org/attachment.cgi?id=24925&action=edit
Resulting assembly (good and bad)
The miscompile is caused by the following patch:
commit 1b748faf2bae246e2fc77d88420df13c2e60f4df
Author: Guozhi Wei <car...@google.com>
Date: Tue Jun 1 10:31:30 2021 -0700
[X86FixupLEAs] Transform the sequence LEA/SUB to SUB/SUB
This patch transforms the sequence
lea (reg1, reg2), reg3
sub reg3, reg4
to two sub instructions
sub reg1, reg4
sub reg2, reg4
Similar optimization can also be applied to LEA/ADD sequence.
The modifications to TwoAddressInstructionPass is to ensure the operands of
ADD
instruction has expected order (the dest register of LEA should be src
register of ADD).
Differential Revision: https://reviews.llvm.org/D101970
The prior revision of this patch was reverted due to a miscompile. We are sill
observing a miscompile, original test is written in Java and I could not easily
make a C++ repro. In attachment - resulting assembly for bad (current trunk)
and good (with the problematic patch reverted) cases, and llc logs with
-print-after-all/print-before-all for each of them
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