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7eae8125c6
Current findBestLoopTop can find and move one kind of block to top, a latch block has one successor. Another common case is:
* a latch block
* it has two successors, one is loop header, another is exit
* it has more than one predecessors
If it is below one of its predecessors P, only P can fall through to it, all other predecessors need a jump to it, and another conditional jump to loop header. If it is moved before loop header, all its predecessors jump to it, then fall through to loop header. So all its predecessors except P can reduce one taken branch.
Differential Revision: https://reviews.llvm.org/D43256
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@363471 91177308-0d34-0410-b5e6-96231b3b80d8
76 lines
3.2 KiB
LLVM
76 lines
3.2 KiB
LLVM
; RUN: llc < %s -mtriple=armv7-apple-darwin | FileCheck %s
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; PHI elimination shouldn't break backedge.
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; rdar://8263994
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%struct.list_data_s = type { i16, i16 }
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%struct.list_head = type { %struct.list_head*, %struct.list_data_s* }
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define arm_apcscc %struct.list_head* @t1(%struct.list_head* %list) nounwind {
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entry:
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; CHECK-LABEL: t1:
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%0 = icmp eq %struct.list_head* %list, null
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br i1 %0, label %bb2, label %bb
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bb:
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; CHECK: LBB0_[[LABEL:[0-9]]]:
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; CHECK: bne LBB0_[[LABEL]]
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; CHECK-NOT: b LBB0_[[LABEL]]
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; CHECK: bx lr
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%list_addr.05 = phi %struct.list_head* [ %2, %bb ], [ %list, %entry ]
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%next.04 = phi %struct.list_head* [ %list_addr.05, %bb ], [ null, %entry ]
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%1 = getelementptr inbounds %struct.list_head, %struct.list_head* %list_addr.05, i32 0, i32 0
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%2 = load %struct.list_head*, %struct.list_head** %1, align 4
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store %struct.list_head* %next.04, %struct.list_head** %1, align 4
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%3 = icmp eq %struct.list_head* %2, null
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br i1 %3, label %bb2, label %bb
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bb2:
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%next.0.lcssa = phi %struct.list_head* [ null, %entry ], [ %list_addr.05, %bb ]
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ret %struct.list_head* %next.0.lcssa
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}
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; Optimize loop entry, eliminate intra loop branches
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; rdar://8117827
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define i32 @t2(i32 %passes, i32* nocapture %src, i32 %size) nounwind readonly {
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entry:
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; CHECK-LABEL: t2:
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%0 = icmp eq i32 %passes, 0 ; <i1> [#uses=1]
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br i1 %0, label %bb5, label %bb.nph15
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bb1: ; preds = %bb2.preheader, %bb1
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; CHECK: LBB1_[[BB3:.]]: @ %bb3
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; CHECK: LBB1_[[PREHDR:.]]: @ %bb2.preheader
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; CHECK: blt LBB1_[[BB3]]
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%indvar = phi i32 [ %indvar.next, %bb1 ], [ 0, %bb2.preheader ] ; <i32> [#uses=2]
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%sum.08 = phi i32 [ %2, %bb1 ], [ %sum.110, %bb2.preheader ] ; <i32> [#uses=1]
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%tmp17 = sub i32 %i.07, %indvar ; <i32> [#uses=1]
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%scevgep = getelementptr i32, i32* %src, i32 %tmp17 ; <i32*> [#uses=1]
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%1 = load i32, i32* %scevgep, align 4 ; <i32> [#uses=1]
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%2 = add nsw i32 %1, %sum.08 ; <i32> [#uses=2]
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%indvar.next = add i32 %indvar, 1 ; <i32> [#uses=2]
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%exitcond = icmp eq i32 %indvar.next, %size ; <i1> [#uses=1]
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br i1 %exitcond, label %bb3, label %bb1
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bb3: ; preds = %bb1, %bb2.preheader
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; CHECK: LBB1_[[BB1:.]]: @ %bb1
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; CHECK: bne LBB1_[[BB1]]
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%sum.0.lcssa = phi i32 [ %sum.110, %bb2.preheader ], [ %2, %bb1 ] ; <i32> [#uses=2]
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%3 = add i32 %pass.011, 1 ; <i32> [#uses=2]
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%exitcond18 = icmp eq i32 %3, %passes ; <i1> [#uses=1]
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br i1 %exitcond18, label %bb5, label %bb2.preheader
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bb.nph15: ; preds = %entry
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%i.07 = add i32 %size, -1 ; <i32> [#uses=2]
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%4 = icmp sgt i32 %i.07, -1 ; <i1> [#uses=1]
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br label %bb2.preheader
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bb2.preheader: ; preds = %bb3, %bb.nph15
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%pass.011 = phi i32 [ 0, %bb.nph15 ], [ %3, %bb3 ] ; <i32> [#uses=1]
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%sum.110 = phi i32 [ 0, %bb.nph15 ], [ %sum.0.lcssa, %bb3 ] ; <i32> [#uses=2]
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br i1 %4, label %bb1, label %bb3
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bb5: ; preds = %bb3, %entry
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%sum.1.lcssa = phi i32 [ 0, %entry ], [ %sum.0.lcssa, %bb3 ] ; <i32> [#uses=1]
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ret i32 %sum.1.lcssa
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}
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