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[MachineTraceMetrics] Pick the trace successor for an entry block 

We generate erroneous trace for a basic block if it does not have at least one
predecessor when MinInstr strategy is used. Currently only this strategy is
implemented, so we always have a wrong trace for any entry block. This results in
wrong instructions heights calculation and also leads to wrong critical path.

The described behavior is demonstrated on a simple test. It shows that early
if-conv pass makes wrong decisions due to incorrectly calculated critical path
lenght.

Differential Revision: https://reviews.llvm.org/D138272
This commit is contained in:
Anton Sidorenko 2022-11-18 12:33:02 +03:00
parent 0c22cdfdd1
commit fb47bb37e4
2 changed files with 11 additions and 11 deletions
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2
llvm/lib/CodeGen/MachineTraceMetrics.cpp
View File

@ -352,7 +352,7 @@ MinInstrCountEnsemble::pickTracePred(const MachineBasicBlock *MBB) {
// Select the preferred successor for MBB.
const MachineBasicBlock*
MinInstrCountEnsemble::pickTraceSucc(const MachineBasicBlock *MBB) {
if (MBB->pred_empty())
if (MBB->succ_empty())
return nullptr;
const MachineLoop *CurLoop = getLoopFor(MBB);
const MachineBasicBlock *Best = nullptr;

20
llvm/test/CodeGen/X86/machine-trace-metrics-entryBB-critpath.ll
View File

@ -6,27 +6,27 @@
; MinInstr strategy is used. The behavior is demonstrated on early if conversion
; pass.
; CHECK: TBB: MinInstr trace %bb.0 --> %bb.0 --> %bb.0: 4 instrs. 1 cycles.
; CHECK: TBB: MinInstr trace %bb.0 --> %bb.0 --> %bb.2: 8 instrs. 30 cycles.
; CHECK: %bb.0
; CHECK: -> %bb.2
; CHECK: FBB: MinInstr trace %bb.0 --> %bb.1 --> %bb.2: 10 instrs. 32 cycles.
; CHECK: %bb.1 <- %bb.0
; CHECK: -> %bb.2
; CHECK: Resource length 10, minimal critical path 1
; CHECK: Not enough available ILP.
; CHECK: Resource length 10, minimal critical path 30
; CHECK: If-converting
define i32 @_Z3fooiidd(i32 %a, i32 %b, double %d, double %e) #0 {
; CHECK-LABEL: _Z3fooiidd:
; CHECK: # %bb.0: # %entry
; CHECK-NEXT: movl %esi, %eax
; CHECK-NEXT: addl %edi, %eax
; CHECK-NEXT: cmpl $3, %edi
; CHECK-NEXT: jl .LBB0_2
; CHECK-NEXT: # %bb.1: # %if.then
; CHECK-NEXT: cvttsd2si %xmm0, %ecx
; CHECK-NEXT: # kill: def $esi killed $esi def $rsi
; CHECK-NEXT: # kill: def $edi killed $edi def $rdi
; CHECK-NEXT: leal (%rsi,%rdi), %ecx
; CHECK-NEXT: cvttsd2si %xmm0, %eax
; CHECK-NEXT: addl %ecx, %eax
; CHECK-NEXT: .LBB0_2: # %if.end
; CHECK-NEXT: cmpl $3, %edi
; CHECK-NEXT: cmovll %ecx, %eax
; CHECK-NEXT: cvttsd2si %xmm1, %ecx
; CHECK-NEXT: cltd
; CHECK-NEXT: idivl %ecx