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[PGO][PGSO] Update BFI in CodeGenPrepare::optimizeSelectInst. 

Summary:
Without the BFI update, some hot blocks are incorrectly treated as cold code.

This fixes a FDO perf regression in the TSVC benchmark from D71288.

Reviewers: davidxl

Subscribers: hiraditya, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D73146
This commit is contained in:
Hiroshi Yamauchi 2020-01-21 15:49:04 -08:00
parent a8ff6c0b09
commit ddbc728828
2 changed files with 26 additions and 0 deletions
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1
llvm/lib/CodeGen/CodeGenPrepare.cpp
View File

@ -6138,6 +6138,7 @@ bool CodeGenPrepare::optimizeSelectInst(SelectInst *SI) {
BasicBlock *StartBlock = SI->getParent();
BasicBlock::iterator SplitPt = ++(BasicBlock::iterator(LastSI));
BasicBlock *EndBlock = StartBlock->splitBasicBlock(SplitPt, "select.end");
BFI->setBlockFreq(EndBlock, BFI->getBlockFreq(StartBlock).getFrequency());
// Delete the unconditional branch that was just created by the split.
StartBlock->getTerminator()->eraseFromParent();

25
llvm/test/CodeGen/X86/cmov-into-branch.ll
View File

@ -165,6 +165,30 @@ define i32 @weighted_select_pgso(i32 %a, i32 %b) !prof !14 {
ret i32 %sel
}
; If two selects in a row are predictable, turn them into branches.
define i32 @weighted_selects(i32 %a, i32 %b) !prof !19 {
; CHECK-LABEL: weighted_selects:
; CHECK: # %bb.0:
; CHECK-NEXT: movl %esi, %eax
; CHECK-NEXT: testl %edi, %edi
; CHECK-NEXT: movl %edi, %ecx
; CHECK-NEXT: jne .LBB11_2
; CHECK-NEXT: # %bb.1: # %select.false
; CHECK-NEXT: movl %eax, %ecx
; CHECK-NEXT: .LBB11_2: # %select.end
; CHECK-NEXT: testl %ecx, %ecx
; CHECK-NEXT: jne .LBB11_4
; CHECK-NEXT: # %bb.3: # %select.false2
; CHECK-NEXT: movl %edi, %eax
; CHECK-NEXT: .LBB11_4: # %select.end1
; CHECK-NEXT: retq
%cmp = icmp ne i32 %a, 0
%sel = select i1 %cmp, i32 %a, i32 %b, !prof !16
%cmp1 = icmp ne i32 %sel, 0
%sel1 = select i1 %cmp1, i32 %b, i32 %a, !prof !16
ret i32 %sel1
}
!llvm.module.flags = !{!0}
!0 = !{i32 1, !"ProfileSummary", !1}
!1 = !{!2, !3, !4, !5, !6, !7, !8, !9}
@ -185,3 +209,4 @@ define i32 @weighted_select_pgso(i32 %a, i32 %b) !prof !14 {
!16 = !{!"branch_weights", i32 1, i32 100}
!17 = !{!"branch_weights", i32 100, i32 1}
!18 = !{!"branch_weights", i32 0, i32 0}
!19 = !{!"function_entry_count", i64 100}