[llvm] r237395 - Add another InstCombine pass after LoopUnroll.

[David Majnemer]

Can we remove the subsequent call to createInstructionSimplifierPass?
InstCombine should be strictly more powerful.

On Thu, May 14, 2015 at 3:02 PM, Wei Mi <wmi at google.com> wrote:

> Author: wmi
> Date: Thu May 14 17:02:54 2015
> New Revision: 237395
>
> URL: http://llvm.org/viewvc/llvm-project?rev=237395&view=rev
> Log:
> Add another InstCombine pass after LoopUnroll.
>
> This is to cleanup some redundency generated by LoopUnroll pass. Such
> redundency may not be cleaned up by existing passes after LoopUnroll.
>
> Differential Revision: http://reviews.llvm.org/D9777
>
> Added:
>     llvm/trunk/test/Transforms/LoopUnroll/unroll-cleanup.ll
> Modified:
>     llvm/trunk/lib/Transforms/IPO/PassManagerBuilder.cpp
>
> Modified: llvm/trunk/lib/Transforms/IPO/PassManagerBuilder.cpp
> URL:
> http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/IPO/PassManagerBuilder.cpp?rev=237395&r1=237394&r2=237395&view=diff
>
> ==============================================================================
> --- llvm/trunk/lib/Transforms/IPO/PassManagerBuilder.cpp (original)
> +++ llvm/trunk/lib/Transforms/IPO/PassManagerBuilder.cpp Thu May 14
> 17:02:54 2015
> @@ -382,6 +382,9 @@ void PassManagerBuilder::populateModuleP
>    if (!DisableUnrollLoops) {
>      MPM.add(createLoopUnrollPass());    // Unroll small loops
>
> +    // LoopUnroll may generate some redundency to cleanup.
> +    MPM.add(createInstructionCombiningPass());
> +
>      // This is a barrier pass to avoid combine LICM pass and loop unroll
> pass
>      // within same loop pass manager.
>      MPM.add(createInstructionSimplifierPass());
>
> Added: llvm/trunk/test/Transforms/LoopUnroll/unroll-cleanup.ll
> URL:
> http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/LoopUnroll/unroll-cleanup.ll?rev=237395&view=auto
>
> ==============================================================================
> --- llvm/trunk/test/Transforms/LoopUnroll/unroll-cleanup.ll (added)
> +++ llvm/trunk/test/Transforms/LoopUnroll/unroll-cleanup.ll Thu May 14
> 17:02:54 2015
> @@ -0,0 +1,85 @@
> +; PR23524
> +; The test is to check redundency produced by loop unroll pass
> +; should be cleaned up by later pass.
> +; RUN: opt < %s -O2 -S | FileCheck %s
> +
> +; After loop unroll:
> +;       %dec18 = add nsw i32 %dec18.in, -1
> +;       ...
> +;       %dec18.1 = add nsw i32 %dec18, -1
> +; should be merged to:
> +;       %dec18.1 = add nsw i32 %dec18.in, -2
> +;
> +; CHECK-LABEL: @_Z3fn1v(
> +; CHECK: %dec18.1 = add nsw i32 %dec18.in, -2
> +
> +; ModuleID = '<stdin>'
> +target triple = "x86_64-unknown-linux-gnu"
> +
> + at b = global i32 0, align 4
> + at c = global i32 0, align 4
> +
> +; Function Attrs: nounwind uwtable
> +define void @_Z3fn1v() #0 {
> +entry:
> +  %tmp = load i32, i32* @b, align 4
> +  %tobool20 = icmp eq i32 %tmp, 0
> +  br i1 %tobool20, label %for.end6, label %for.body.lr.ph
> +
> +for.body.lr.ph:                                   ; preds = %entry
> +  br label %for.body
> +
> +for.cond1.for.cond.loopexit_crit_edge:            ; preds = %for.inc
> +  %add.ptr.lcssa = phi i16* [ %add.ptr, %for.inc ]
> +  %incdec.ptr.lcssa = phi i8* [ %incdec.ptr, %for.inc ]
> +  br label %for.cond.loopexit
> +
> +for.cond.loopexit:                                ; preds = %for.body,
> %for.cond1.for.cond.loopexit_crit_edge
> +  %r.1.lcssa = phi i16* [ %add.ptr.lcssa,
> %for.cond1.for.cond.loopexit_crit_edge ], [ %r.022, %for.body ]
> +  %a.1.lcssa = phi i8* [ %incdec.ptr.lcssa,
> %for.cond1.for.cond.loopexit_crit_edge ], [ %a.021, %for.body ]
> +  %tmp1 = load i32, i32* @b, align 4
> +  %tobool = icmp eq i32 %tmp1, 0
> +  br i1 %tobool, label %for.cond.for.end6_crit_edge, label %for.body
> +
> +for.body:                                         ; preds =
> %for.cond.loopexit, %for.body.lr.ph
> +  %r.022 = phi i16* [ undef, %for.body.lr.ph ], [ %r.1.lcssa,
> %for.cond.loopexit ]
> +  %a.021 = phi i8* [ undef, %for.body.lr.ph ], [ %a.1.lcssa,
> %for.cond.loopexit ]
> +  %tmp2 = load i32, i32* @c, align 4
> +  %tobool215 = icmp eq i32 %tmp2, 0
> +  br i1 %tobool215, label %for.cond.loopexit, label %for.body3.lr.ph
> +
> +for.body3.lr.ph:                                  ; preds = %for.body
> +  br label %for.body3
> +
> +for.body3:                                        ; preds = %for.inc, %
> for.body3.lr.ph
> +  %dec18.in = phi i32 [ %tmp2, %for.body3.lr.ph ], [ %dec18, %for.inc ]
> +  %r.117 = phi i16* [ %r.022, %for.body3.lr.ph ], [ %add.ptr, %for.inc ]
> +  %a.116 = phi i8* [ %a.021, %for.body3.lr.ph ], [ %incdec.ptr, %for.inc
> ]
> +  %dec18 = add nsw i32 %dec18.in, -1
> +  %tmp3 = load i8, i8* %a.116, align 1
> +  %cmp = icmp eq i8 %tmp3, 0
> +  br i1 %cmp, label %if.then, label %for.inc
> +
> +if.then:                                          ; preds = %for.body3
> +  %arrayidx = getelementptr inbounds i16, i16* %r.117, i64 1
> +  store i16 0, i16* %arrayidx, align 2
> +  store i16 0, i16* %r.117, align 2
> +  %arrayidx5 = getelementptr inbounds i16, i16* %r.117, i64 2
> +  store i16 0, i16* %arrayidx5, align 2
> +  br label %for.inc
> +
> +for.inc:                                          ; preds = %if.then,
> %for.body3
> +  %incdec.ptr = getelementptr inbounds i8, i8* %a.116, i64 1
> +  %add.ptr = getelementptr inbounds i16, i16* %r.117, i64 3
> +  %tobool2 = icmp eq i32 %dec18, 0
> +  br i1 %tobool2, label %for.cond1.for.cond.loopexit_crit_edge, label
> %for.body3, !llvm.loop !0
> +
> +for.cond.for.end6_crit_edge:                      ; preds =
> %for.cond.loopexit
> +  br label %for.end6
> +
> +for.end6:                                         ; preds =
> %for.cond.for.end6_crit_edge, %entry
> +  ret void
> +}
> +
> +!0 = !{!0, !1}
> +!1 = !{!"llvm.loop.unroll.count", i32 2}
>
>
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