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[MBP] findBestLoopTopHelper should exit if OldTop is not a chain header 

Function findBestLoopTopHelper tries to find a new loop top block which can also
fall through to OldTop, but it's impossible if OldTop is not a chain header, so
it should exit immediately.

Differential Revision: https://reviews.llvm.org/D106329
This commit is contained in:
Guozhi Wei 2021-07-28 19:00:45 -07:00
parent 264b8e2a20
commit 50b6273145
2 changed files with 67 additions and 0 deletions
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2
llvm/lib/CodeGen/MachineBlockPlacement.cpp
View File

@ -2050,6 +2050,8 @@ MachineBlockPlacement::findBestLoopTopHelper(
BlockChain &HeaderChain = *BlockToChain[OldTop];
if (!LoopBlockSet.count(*HeaderChain.begin()))
return OldTop;
if (OldTop != *HeaderChain.begin())
return OldTop;
LLVM_DEBUG(dbgs() << "Finding best loop top for: " << getBlockName(OldTop)
<< "\n");

65
llvm/test/CodeGen/ARM/mbp.ll Normal file
View File

@ -0,0 +1,65 @@
; RUN: llc < %s | FileCheck %s
target datalayout = "e-m:e-p:32:32-Fi8-i64:64-v128:64:128-a:0:32-n32-S64"
target triple = "thumbv7-unknown-linux-gnueabihf"
%Target = type { %Target*, %List* }
%List = type { i32, i32* }
; The entry block should be the first block of the function.
; CHECK-LABEL: foo
; CHECK: %entry
; CHECK: %for.body
; CHECK: %for.inc
; CHECK: %if.then
; CHECK: %for.cond.i
; CHECK: %for.body.i
; CHECK: %return
define i1 @foo(%Target** %ha, i32 %he) !prof !39 {
entry:
%TargetPtr = load %Target*, %Target** %ha, align 4
%cmp1 = icmp eq %Target* %TargetPtr, null
br i1 %cmp1, label %return, label %for.body, !prof !50
for.body:
%TargetPhi = phi %Target* [ %NextPtr, %for.inc ], [ %TargetPtr, %entry ]
%ListAddr = getelementptr inbounds %Target, %Target* %TargetPhi, i32 0, i32 1
%ListPtr = load %List*, %List** %ListAddr, align 4
%cmp2 = icmp eq %List* %ListPtr, null
br i1 %cmp2, label %for.inc, label %if.then, !prof !59
if.then:
%lenAddr = getelementptr inbounds %List, %List* %ListPtr, i32 0, i32 0
%len = load i32, i32* %lenAddr, align 4
%ptr = getelementptr inbounds %List, %List* %ListPtr, i32 0, i32 1
%ptr2 = load i32*, i32** %ptr, align 4
br label %for.cond.i
for.cond.i:
%i = phi i32 [ %len, %if.then ], [ %index, %for.body.i ]
%index = add nsw i32 %i, -1
%cmp3 = icmp sgt i32 %i, 0
br i1 %cmp3, label %for.body.i, label %for.inc, !prof !75
for.body.i:
%ptr3 = getelementptr inbounds i32, i32* %ptr2, i32 %index
%data = load i32, i32* %ptr3, align 4
%cmp4 = icmp eq i32 %data, %he
br i1 %cmp4, label %return, label %for.cond.i, !prof !79
for.inc:
%NextAddr = getelementptr inbounds %Target, %Target* %TargetPhi, i32 0, i32 0
%NextPtr = load %Target*, %Target** %NextAddr, align 4
%cmp5 = icmp eq %Target* %NextPtr, null
br i1 %cmp5, label %return, label %for.body, !prof !50
return:
%retval = phi i1 [ false, %entry ], [ true, %for.body.i ], [ false, %for.inc ]
ret i1 %retval
}
!39 = !{!"function_entry_count", i64 226}
!50 = !{!"branch_weights", i32 451, i32 1}
!59 = !{!"branch_weights", i32 1502, i32 1}
!75 = !{!"branch_weights", i32 301, i32 1}
!79 = !{!"branch_weights", i32 1, i32 301}