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Skip over prefetches

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Summary: Skip over prefetches when assigning debug info to instructions with memory operands. This way, the debug info is stable after instrumenting a binary with prefetches, allowing for iterative profiling and instrumentation.

Reviewers: davidxl

Reviewed By: davidxl

Subscribers: aprantl, hiraditya, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D61789

llvm-svn: 360471
This commit is contained in:
Mircea Trofin 2019-05-10 21:27:55 +00:00
parent f446282678
commit 3a40b69c29
2 changed files with 85 additions and 0 deletions
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16
lib/Target/X86/X86DiscriminateMemOps.cpp
View File

@ -34,6 +34,14 @@ static cl::opt<bool> EnableDiscriminateMemops(
"the build of the binary consuming the profile."),
cl::Hidden);
static cl::opt<bool> BypassPrefetchInstructions(
"x86-bypass-prefetch-instructions", cl::init(true),
cl::desc("When discriminating instructions with memory operands, ignore "
"prefetch instructions. This ensures the other memory operand "
"instructions have the same identifiers after inserting "
"prefetches, allowing for successive insertions."),
cl::Hidden);
namespace {
using Location = std::pair<StringRef, unsigned>;
@ -62,6 +70,10 @@ public:
X86DiscriminateMemOps();
};
bool IsPrefetchOpcode(unsigned Opcode) {
return Opcode == X86::PREFETCHNTA || Opcode == X86::PREFETCHT0 ||
Opcode == X86::PREFETCHT1 || Opcode == X86::PREFETCHT2;
}
} // end anonymous namespace
//===----------------------------------------------------------------------===//
@ -98,6 +110,8 @@ bool X86DiscriminateMemOps::runOnMachineFunction(MachineFunction &MF) {
const auto &DI = MI.getDebugLoc();
if (!DI)
continue;
if (BypassPrefetchInstructions && IsPrefetchOpcode(MI.getDesc().Opcode))
continue;
Location Loc = diToLocation(DI);
MemOpDiscriminators[Loc] =
std::max(MemOpDiscriminators[Loc], DI->getBaseDiscriminator());
@ -114,6 +128,8 @@ bool X86DiscriminateMemOps::runOnMachineFunction(MachineFunction &MF) {
for (auto &MI : MBB) {
if (X86II::getMemoryOperandNo(MI.getDesc().TSFlags) < 0)
continue;
if (BypassPrefetchInstructions && IsPrefetchOpcode(MI.getDesc().Opcode))
continue;
const DILocation *DI = MI.getDebugLoc();
bool HasDebug = DI;
if (!HasDebug) {

69
test/CodeGen/X86/discriminate-mem-ops-skip-pfetch.ll Normal file
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@ -0,0 +1,69 @@
; RUN: llc -x86-discriminate-memops < %s | FileCheck %s
; RUN: llc -x86-discriminate-memops -x86-bypass-prefetch-instructions=0 < %s | FileCheck %s -check-prefix=NOBYPASS
;
; original source, compiled with -O3 -gmlt -fdebug-info-for-profiling:
; int sum(int* arr, int pos1, int pos2) {
; return arr[pos1] + arr[pos2];
; }
;
; ModuleID = 'test.cc'
source_filename = "test.cc"
target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
target triple = "x86_64-unknown-linux-gnu"
declare void @llvm.prefetch(i8 *, i32, i32, i32)
; Function Attrs: norecurse nounwind readonly uwtable
define i32 @sum(i32* %arr, i32 %pos1, i32 %pos2) !dbg !7 {
entry:
%idxprom = sext i32 %pos1 to i64, !dbg !9
%arrayidx = getelementptr inbounds i32, i32* %arr, i64 %idxprom, !dbg !9
%0 = load i32, i32* %arrayidx, align 4, !dbg !9, !tbaa !10
%idxprom1 = sext i32 %pos2 to i64, !dbg !14
%arrayidx2 = getelementptr inbounds i32, i32* %arr, i64 %idxprom1, !dbg !14
%addr = bitcast i32* %arrayidx2 to i8*
call void @llvm.prefetch(i8* %addr, i32 0, i32 3, i32 1)
%1 = load i32, i32* %arrayidx2, align 4, !dbg !14, !tbaa !10
%add = add nsw i32 %1, %0, !dbg !15
ret i32 %add, !dbg !16
}
attributes #0 = { "target-cpu"="x86-64" }
!llvm.dbg.cu = !{!0}
!llvm.module.flags = !{!3, !4, !5}
!llvm.ident = !{!6}
!0 = distinct !DICompileUnit(language: DW_LANG_C_plus_plus, file: !1, isOptimized: true, runtimeVersion: 0, emissionKind: LineTablesOnly, enums: !2, debugInfoForProfiling: true)
!1 = !DIFile(filename: "test.cc", directory: "/tmp")
!2 = !{}
!3 = !{i32 2, !"Dwarf Version", i32 4}
!4 = !{i32 2, !"Debug Info Version", i32 3}
!5 = !{i32 1, !"wchar_size", i32 4}
!6 = !{!"clang version 7.0.0 (trunk 322155) (llvm/trunk 322159)"}
!7 = distinct !DISubprogram(name: "sum", linkageName: "sum", scope: !1, file: !1, line: 1, type: !8, isLocal: false, isDefinition: true, scopeLine: 1, flags: DIFlagPrototyped, isOptimized: true, unit: !0)
!8 = !DISubroutineType(types: !2)
!9 = !DILocation(line: 2, column: 10, scope: !7)
!10 = !{!11, !11, i64 0}
!11 = !{!"int", !12, i64 0}
!12 = !{!"omnipotent char", !13, i64 0}
!13 = !{!"Simple C++ TBAA"}
!14 = !DILocation(line: 2, column: 22, scope: !7)
!15 = !DILocation(line: 2, column: 20, scope: !7)
!16 = !DILocation(line: 2, column: 3, scope: !7)
;CHECK-LABEL: sum:
;CHECK: # %bb.0:
;CHECK: prefetcht0 (%rdi,%rax,4)
;CHECK-NEXT: movl (%rdi,%rax,4), %eax
;CHECK-NEXT: .loc 1 2 20 discriminator 2 # test.cc:2:20
;CHECK-NEXT: addl (%rdi,%rcx,4), %eax
;CHECK-NEXT: .loc 1 2 3 # test.cc:2:3
;NOBYPASS-LABEL: sum:
;NOBYPASS: # %bb.0:
;NOBYPASS: prefetcht0 (%rdi,%rax,4)
;NOBYPASS-NEXT: .loc 1 2 22
;NOBYPASS-NEXT: movl (%rdi,%rax,4), %eax
;NOBYPASS-NEXT: .loc 1 2 20 {{.*}} discriminator 2 # test.cc:2:20
;NOBYPASS-NEXT: addl (%rdi,%rcx,4), %eax
;NOBYPASS-NEXT: .loc 1 2 3 # test.cc:2:3