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[CodeGen] Allow partial tail duplication in Machine Block Placement. 

Summary: A count profile may affect tail duplication's heuristic causing a block to be duplicated in only a part of its predecessors. This is not allowed in the Machine Block Placement pass where an assert will go off. I'm removing the assert and making the optimization bail out when such case happens.

Reviewers: wenlei, davidxl, Carrot

Reviewed By: Carrot

Subscribers: hiraditya, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D77748
This commit is contained in:
Hongtao Yu 2020-04-11 12:20:12 -07:00 committed by Wenlei He
parent b96b9335ae
commit 11455a7905
2 changed files with 87 additions and 6 deletions
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8
llvm/lib/CodeGen/MachineBlockPlacement.cpp
View File

@ -2914,10 +2914,7 @@ bool MachineBlockPlacement::repeatedlyTailDuplicateBlock(
// duplicated into is still small enough to be duplicated again.
// No need to call markBlockSuccessors in this case, as the blocks being
// duplicated from here on are already scheduled.
// Note that DuplicatedToLPred always implies Removed.
while (DuplicatedToLPred) {
assert(Removed && "Block must have been removed to be duplicated into its "
"layout predecessor.");
while (DuplicatedToLPred && Removed) {
MachineBasicBlock *DupBB, *DupPred;
// The removal callback causes Chain.end() to be updated when a block is
// removed. On the first pass through the loop, the chain end should be the
@ -2956,8 +2953,7 @@ bool MachineBlockPlacement::repeatedlyTailDuplicateBlock(
/// chosen in the given order due to unnatural CFG
/// only needed if \p BB is removed and
/// \p PrevUnplacedBlockIt pointed to \p BB.
/// \p DuplicatedToLPred - True if the block was duplicated into LPred. Will
/// only be true if the block was removed.
/// \p DuplicatedToLPred - True if the block was duplicated into LPred.
/// \return - True if the block was duplicated into all preds and removed.
bool MachineBlockPlacement::maybeTailDuplicateBlock(
MachineBasicBlock *BB, MachineBasicBlock *LPred,

85
llvm/test/CodeGen/X86/tail-dup-partial.ll Normal file
View File

@ -0,0 +1,85 @@
; RUN: llc < %s -mtriple=x86_64-unknown-linux-gnu -O3 | FileCheck %s
; Function Attrs: uwtable
; When tail-duplicating during placement, we work backward from blocks with
; multiple successors. In this case, the block dup1 gets duplicated into dup2
; and if.then64, and then the block dup2 only gets duplicated into land.lhs.true.
define void @partial_tail_dup(i1 %a1, i1 %a2, i32* %a4, i32* %a5, i8* %a6, i32 %a7) #0 align 2 !prof !1 {
; CHECK-LABEL: partial_tail_dup:
; CHECK: # %bb.0: # %entry
; CHECK-NEXT: .p2align 4, 0x90
; CHECK-NEXT: .LBB0_1: # %for.cond
; CHECK-NEXT: # =>This Inner Loop Header: Depth=1
; CHECK-NEXT: testb $1, %dil
; CHECK-NEXT: je .LBB0_3
; CHECK-NEXT: # %bb.2: # %land.lhs.true
; CHECK-NEXT: # in Loop: Header=BB0_1 Depth=1
; CHECK-NEXT: movl $10, (%rdx)
; CHECK-NEXT: movl $2, (%rcx)
; CHECK-NEXT: testl %r9d, %r9d
; CHECK-NEXT: je .LBB0_1
; CHECK-NEXT: jmp .LBB0_8
; CHECK-NEXT: .p2align 4, 0x90
; CHECK-NEXT: .LBB0_6: # %dup2
; CHECK-NEXT: # in Loop: Header=BB0_1 Depth=1
; CHECK-NEXT: movl $2, (%rcx)
; CHECK-NEXT: testl %r9d, %r9d
; CHECK-NEXT: je .LBB0_1
; CHECK-NEXT: jmp .LBB0_8
; CHECK-NEXT: .p2align 4, 0x90
; CHECK-NEXT: .LBB0_3: # %if.end56
; CHECK-NEXT: # in Loop: Header=BB0_1 Depth=1
; CHECK-NEXT: testb $1, %sil
; CHECK-NEXT: je .LBB0_5
; CHECK-NEXT: # %bb.4: # %if.then64
; CHECK-NEXT: # in Loop: Header=BB0_1 Depth=1
; CHECK-NEXT: movb $1, (%r8)
; CHECK-NEXT: testl %r9d, %r9d
; CHECK-NEXT: je .LBB0_1
; CHECK-NEXT: jmp .LBB0_8
; CHECK-NEXT: .LBB0_5: # %if.end70
; CHECK-NEXT: # in Loop: Header=BB0_1 Depth=1
; CHECK-NEXT: movl $12, (%rdx)
; CHECK-NEXT: jne .LBB0_6
; CHECK-NEXT: .LBB0_8: # %for.end
; CHECK-NEXT: retq
entry:
br label %for.cond
for.cond:
br i1 %a1, label %land.lhs.true, label %if.end56
land.lhs.true:
store i32 10, i32* %a4, align 8
br label %dup2
if.end56:
br i1 %a2, label %if.then64, label %if.end70, !prof !2
if.then64:
store i8 1, i8* %a6, align 1
br label %dup1
if.end70:
store i32 12, i32* %a4, align 8
br i1 %a2, label %dup2, label %for.end
dup2:
store i32 2, i32* %a5, align 4
br label %dup1
dup1:
%val = load i32, i32* %a4, align 8
%switch = icmp ult i32 %a7, 1
br i1 %switch, label %for.cond, label %for.end, !prof !3
for.end:
ret void
}
attributes #0 = { uwtable }
!1 = !{!"function_entry_count", i64 2}
!2 = !{!"branch_weights", i32 5, i32 1}
!3 = !{!"branch_weights", i32 5, i32 1}