[llvm] r264099 - Keep CodeGenPrepare from preserving the domtree.

[Quentin Colombet via llvm-commits]

Hi George,

Would it be easy to teach CGP how to update it?

We have the availableIf idiom or something for such cases and that would avoid invalidating the whole thing.

(Just asking, I don’t actually what in CGP invalidates the DomTree.)

Cheers,
-Quentin
> On Mar 22, 2016, at 2:25 PM, George Burgess IV via llvm-commits <llvm-commits at lists.llvm.org> wrote:
> 
> Author: gbiv
> Date: Tue Mar 22 16:25:08 2016
> New Revision: 264099
> 
> URL: http://llvm.org/viewvc/llvm-project?rev=264099&view=rev
> Log:
> Keep CodeGenPrepare from preserving the domtree.
> 
> CGP modifies the domtree in some cases, so saying that it preserves the
> domtree is a lie. We'll be able to selectively preserve it with the new
> pass manager.
> 
> Differential Revision: http://reviews.llvm.org/D16893
> 
> Added:
>    llvm/trunk/test/Transforms/CodeGenPrepare/dom-tree.ll
> Modified:
>    llvm/trunk/lib/CodeGen/CodeGenPrepare.cpp
> 
> Modified: llvm/trunk/lib/CodeGen/CodeGenPrepare.cpp
> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/CodeGen/CodeGenPrepare.cpp?rev=264099&r1=264098&r2=264099&view=diff
> ==============================================================================
> --- llvm/trunk/lib/CodeGen/CodeGenPrepare.cpp (original)
> +++ llvm/trunk/lib/CodeGen/CodeGenPrepare.cpp Tue Mar 22 16:25:08 2016
> @@ -158,7 +158,7 @@ class TypePromotionTransaction;
>     const char *getPassName() const override { return "CodeGen Prepare"; }
> 
>     void getAnalysisUsage(AnalysisUsage &AU) const override {
> -      AU.addPreserved<DominatorTreeWrapperPass>();
> +      // FIXME: When we can selectively preserve passes, preserve the domtree.
>       AU.addRequired<TargetLibraryInfoWrapperPass>();
>       AU.addRequired<TargetTransformInfoWrapperPass>();
>     }
> @@ -5277,6 +5277,7 @@ bool CodeGenPrepare::optimizeBlock(Basic
>     for (auto &I : reverse(BB)) {
>       if (makeBitReverse(I, *DL, *TLI)) {
>         MadeBitReverse = MadeChange = true;
> +        ModifiedDT = true;
>         break;
>       }
>     }
> 
> Added: llvm/trunk/test/Transforms/CodeGenPrepare/dom-tree.ll
> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/CodeGenPrepare/dom-tree.ll?rev=264099&view=auto
> ==============================================================================
> --- llvm/trunk/test/Transforms/CodeGenPrepare/dom-tree.ll (added)
> +++ llvm/trunk/test/Transforms/CodeGenPrepare/dom-tree.ll Tue Mar 22 16:25:08 2016
> @@ -0,0 +1,41 @@
> +; RUN: opt -S -loop-unroll -codegenprepare < %s -domtree -analyze | FileCheck %s
> +;
> +; Checks that the dom tree is properly invalidated after an operation that will
> +; invalidate it in CodeGenPrepare. If the domtree isn't properly invalidated,
> +; this will likely segfault, or print badref.
> +
> +; CHECK-NOT: <badref>
> +
> +target datalayout = "e-m:e-p:32:32-i64:64-v128:64:128-a:0:32-n32-S64"
> +target triple = "armv7--linux-gnueabihf"
> +
> +define i32 @f(i32 %a) #0 {
> +entry:
> +  br label %for.body
> +
> +for.cond.cleanup:
> +  ret i32 %or
> +
> +for.body:
> +  %i.08 = phi i32 [ 0, %entry ], [ %inc, %for.body ]
> +  %b.07 = phi i32 [ 0, %entry ], [ %or, %for.body ]
> +  %shr = lshr i32 %a, %i.08
> +  %and = and i32 %shr, 1
> +  %sub = sub nuw nsw i32 31, %i.08
> +  %shl = shl i32 %and, %sub
> +  %or = or i32 %shl, %b.07
> +  %inc = add nuw nsw i32 %i.08, 1
> +  %exitcond = icmp eq i32 %inc, 32
> +  br i1 %exitcond, label %for.cond.cleanup, label %for.body, !llvm.loop !3
> +}
> +
> +attributes #0 = { norecurse nounwind readnone "disable-tail-calls"="false" "less-precise-fpmad"="false" "no-frame-pointer-elim"="true" "no-frame-pointer-elim-non-leaf" "no-infs-fp-math"="false" "no-nans-fp-math"="false" "stack-protector-buffer-size"="8" "target-cpu"="cortex-a8" "target-features"="+dsp,+neon,+vfp3" "unsafe-fp-math"="false" "use-soft-float"="false" }
> +
> +!llvm.module.flags = !{!0, !1}
> +!llvm.ident = !{!2}
> +
> +!0 = !{i32 1, !"wchar_size", i32 4}
> +!1 = !{i32 1, !"min_enum_size", i32 4}
> +!2 = !{!"clang version 3.8.0 (http://llvm.org/git/clang.git b7441a0f42c43a8eea9e3e706be187252db747fa)"}
> +!3 = distinct !{!3, !4}
> +!4 = !{!"llvm.loop.unroll.full"}
> 
> 
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