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memset/memcpy analysis/optimizations need improving #824

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llvmbot opened this issue Oct 20, 2004 · 6 comments
Closed

memset/memcpy analysis/optimizations need improving #824

llvmbot opened this issue Oct 20, 2004 · 6 comments
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bugzilla Issues migrated from bugzilla code-quality ipo

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@llvmbot
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llvmbot commented Oct 20, 2004

Bugzilla Link 452
Resolution FIXED
Resolved on Apr 22, 2009 04:37
Version trunk
OS All
Depends On llvm/llvm-bugzilla-archive#2058 llvm/llvm-bugzilla-archive#1226 llvm/llvm-bugzilla-archive#1952 llvm/llvm-bugzilla-archive#2059
Reporter LLVM Bugzilla Contributor

Extended Description

Just so this doesn't get lost, I'm filing a "wishlist" item for this.

Date: Wed, 6 Oct 2004 14:25:30 -0500 (CDT)
From: Chris Lattner sabre@nondot.org
Subject: memset optimizations

memset currently inhibits multiple optimizations, e.g. memset/load doesn't
get copy-propagated, memset doesn't cause dead stores to die, and memset
inhibits SRA. This should be fixed!

Also: memset(&X, 4) -> store int 0, X iff X is aligned

Also, memset should not kill unaliased loads/stores.

@llvmbot
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llvmbot commented Apr 5, 2007

Edits a hard-coded string in an unrolled loop
I was told in the IRC channel that the non optimized LLVM code I was getting of
the attached C++ code was related to this issue.
It becomes optimized when the string 's' becomes small, like "this".

@lattner
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lattner commented Apr 9, 2007

Bug 1309 is also related to this.

@llvmbot
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llvmbot commented Jan 29, 2008

example with poor memcpy optimization
In the last line
return r + x.A;
the value of x.A is zero, but LLVM doesn't understand this.
Presumably this is because it thinks memcpy has modified x,
even though it copies from x and not to it.

@lattner
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lattner commented Jan 29, 2008

Bug 1952 is one specific optimization that we can do, relating it.

@llvmbot
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llvmbot commented Apr 9, 2008

This has gotten a lot better recently, with work Chris and I have done which is now in the MemCpyOpt pass. There's still a lot to do, though.

@llvmbot
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llvmbot commented Apr 22, 2009

I'm closing this open-ended bug, as we'll never catch EVERY case. If you still have specific cases that you'd like to see addressed, please file individual PRs for them.

@llvmbot llvmbot transferred this issue from llvm/llvm-bugzilla-archive Dec 3, 2021
kwk pushed a commit to kwk/llvm-project that referenced this issue Feb 1, 2022
This issue was closed.
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