[llvm-dev] Optimization issues (Alias Analysis?)

[Hal Finkel via llvm-dev]

Hi Nick, 

We really don't do AA on inttoptr at all. You should use i8* (or some other appropriate pointer type) and GEPs instead. 

-Hal 

----- Original Message -----

> From: "Peet Nick via llvm-dev" <llvm-dev at lists.llvm.org>
> To: llvm-dev at lists.llvm.org
> Sent: Monday, July 4, 2016 11:05:11 AM
> Subject: [llvm-dev] Optimization issues (Alias Analysis?)

> Hey,

> I am currently working on a VM which is based on LLVM and I would
> like to use its optimizer, but it somehow it can't detect something
> very simple (I guess.)

> This is the LLVM IR:

> target datalayout = "e-m:e-p:32:32-f64:32:64-f80:32-n8:16:32-S128"
> target triple = "i386-unknown-linux-gnu"

> %struct.regs = type { i32, i32, i32 }

> define void @Test(%struct.regs* noalias nocapture sret, i32, i32,
> i32) local_unnamed_addr #0 {
> %5 = add i32 %3, -4
> %6 = inttoptr i32 %5 to i32*
> store i32 %2, i32* %6, align 4

> %7 = add i32 %3, -8
> %8 = inttoptr i32 %7 to i32*
> store i32 %1, i32* %8, align 4

> %9 = load i32, i32* %6, align 4

> %.sroa.0.0..sroa_idx = getelementptr inbounds %struct.regs,
> %struct.regs* %0, i32 0, i32 0
> store i32 %9, i32* %.sroa.0.0..sroa_idx, align 4

> %.sroa.4.0..sroa_idx4 = getelementptr inbounds %struct.regs,
> %struct.regs* %0, i32 0, i32 1
> store i32 %1, i32* %.sroa.4.0..sroa_idx4, align 4

> %.sroa.7.0..sroa_idx5 = getelementptr inbounds %struct.regs,
> %struct.regs* %0, i32 0, i32 2
> store i32 %3, i32* %.sroa.7.0..sroa_idx5, align 4

> ret void
> }

> This is compiled from some cpp just to reproduce the issue.
> The issue here is that the load isn't eliminated and that the third
> store isn't directly using %2.

> I thought that this might be an issue with the current
> BasicAliasAnalysis so I also tried CFL which isn't working either.

> ~ Nick
> _______________________________________________
> LLVM Developers mailing list
> llvm-dev at lists.llvm.org
> http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev

-- 

Hal Finkel 
Assistant Computational Scientist 
Leadership Computing Facility 
Argonne National Laboratory 
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