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[AIX][PowerPC][PGO] Generate .ref for some PGO sections

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For PGO on AIX, when we switch to the linux-style PGO variable access
(via _start and _stop labels), we need the compiler to generate a .ref
assembly for each of the three csects:

 -   __llvm_prf_data[RW]
 -   __llvm_prf_names[RO]
 -   __llvm_prf_vnds[RW]

We insert the .ref inside the __llvm_prf_cnts[RW] csect so that if it's
live then the 3 csects are live.

For example, for a testcase with at least one function definition, when
compiled with -fprofile-generate we should generate:

        .csect __llvm_prf_cnts[RW],3
        .ref __llvm_prf_data[RW]   <<============ needs to be inserted
        .ref __llvm_prf_names[RO]  <<===========

the __llvm_prf_vnds is not always present, so we reference it only when
it's present.

Reviewed By: sfertile, daltenty

Differential Revision: https://reviews.llvm.org/D116607
This commit is contained in:
Wael Yehia 2022-02-05 00:08:21 -05:00
parent 24c12bfb33
commit addd073325
8 changed files with 141 additions and 0 deletions
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3
llvm/include/llvm/MC/MCContext.h
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@ -650,6 +650,9 @@ namespace llvm {
unsigned Flags, const MCSymbolWasm *Group,
unsigned UniqueID, const char *BeginSymName);
bool hasXCOFFSection(StringRef Section,
XCOFF::CsectProperties CsectProp) const;
MCSectionXCOFF *getXCOFFSection(
StringRef Section, SectionKind K,
Optional<XCOFF::CsectProperties> CsectProp = None,

6
llvm/include/llvm/MC/MCStreamer.h
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@ -615,6 +615,12 @@ public:
/// changed at the end of assembly.
virtual void emitXCOFFRenameDirective(const MCSymbol *Name, StringRef Rename);
/// Emit a XCOFF .ref directive which creates R_REF type entry in the
/// relocation table for one or more symbols.
///
/// \param Sym - The symbol on the .ref directive.
virtual void emitXCOFFRefDirective(StringRef Sym);
/// Emit an ELF .size directive.
///
/// This corresponds to an assembler statement such as:

4
llvm/include/llvm/MC/MCXCOFFStreamer.h
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@ -32,6 +32,10 @@ public:
void emitXCOFFSymbolLinkageWithVisibility(MCSymbol *Symbol,
MCSymbolAttr Linkage,
MCSymbolAttr Visibility) override;
void emitXCOFFRefDirective(StringRef Name) override {
report_fatal_error("emitXCOFFRefDirective is not implemented yet on object"
"generation path");
}
void emitXCOFFRenameDirective(const MCSymbol *Name,
StringRef Rename) override {
report_fatal_error("emitXCOFFRenameDirective is not implemented yet on "

7
llvm/lib/MC/MCAsmStreamer.cpp
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@ -198,6 +198,8 @@ public:
void emitXCOFFRenameDirective(const MCSymbol *Name,
StringRef Rename) override;
void emitXCOFFRefDirective(StringRef Name) override;
void emitELFSize(MCSymbol *Symbol, const MCExpr *Value) override;
void emitCommonSymbol(MCSymbol *Symbol, uint64_t Size,
unsigned ByteAlignment) override;
@ -931,6 +933,11 @@ void MCAsmStreamer::emitXCOFFRenameDirective(const MCSymbol *Name,
EmitEOL();
}
void MCAsmStreamer::emitXCOFFRefDirective(StringRef Name) {
OS << "\t.ref " << Name;
EmitEOL();
}
void MCAsmStreamer::emitELFSize(MCSymbol *Symbol, const MCExpr *Value) {
assert(MAI->hasDotTypeDotSizeDirective());
OS << "\t.size\t";

6
llvm/lib/MC/MCContext.cpp
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@ -732,6 +732,12 @@ MCSectionWasm *MCContext::getWasmSection(const Twine &Section, SectionKind Kind,
return Result;
}
bool MCContext::hasXCOFFSection(StringRef Section,
XCOFF::CsectProperties CsectProp) const {
return XCOFFUniquingMap.count(
XCOFFSectionKey(Section.str(), CsectProp.MappingClass)) != 0;
}
MCSectionXCOFF *MCContext::getXCOFFSection(
StringRef Section, SectionKind Kind,
Optional<XCOFF::CsectProperties> CsectProp, bool MultiSymbolsAllowed,

4
llvm/lib/MC/MCStreamer.cpp
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@ -1180,6 +1180,10 @@ void MCStreamer::emitXCOFFRenameDirective(const MCSymbol *Name,
"XCOFF targets");
}
void MCStreamer::emitXCOFFRefDirective(StringRef Name) {
llvm_unreachable("emitXCOFFRefDirective is only supported on XCOFF targets");
}
void MCStreamer::emitELFSize(MCSymbol *Symbol, const MCExpr *Value) {}
void MCStreamer::emitELFSymverDirective(const MCSymbol *OriginalSym,
StringRef Name, bool KeepOriginalSym) {}

29
llvm/lib/Target/PowerPC/PPCAsmPrinter.cpp
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@ -254,6 +254,8 @@ public:
void emitFunctionBodyEnd() override;
void emitPGORefs();
void emitEndOfAsmFile(Module &) override;
void emitLinkage(const GlobalValue *GV, MCSymbol *GVSym) const override;
@ -2475,12 +2477,39 @@ void PPCAIXAsmPrinter::emitFunctionEntryLabel() {
});
}
void PPCAIXAsmPrinter::emitPGORefs() {
if (OutContext.hasXCOFFSection(
"__llvm_prf_cnts",
XCOFF::CsectProperties(XCOFF::XMC_RW, XCOFF::XTY_SD))) {
MCSection *CntsSection = OutContext.getXCOFFSection(
"__llvm_prf_cnts", SectionKind::getData(),
XCOFF::CsectProperties(XCOFF::XMC_RW, XCOFF::XTY_SD),
/*MultiSymbolsAllowed*/ true);
OutStreamer->SwitchSection(CntsSection);
if (OutContext.hasXCOFFSection(
"__llvm_prf_data",
XCOFF::CsectProperties(XCOFF::XMC_RW, XCOFF::XTY_SD)))
OutStreamer->emitXCOFFRefDirective("__llvm_prf_data[RW]");
if (OutContext.hasXCOFFSection(
"__llvm_prf_names",
XCOFF::CsectProperties(XCOFF::XMC_RO, XCOFF::XTY_SD)))
OutStreamer->emitXCOFFRefDirective("__llvm_prf_names[RO]");
if (OutContext.hasXCOFFSection(
"__llvm_prf_vnds",
XCOFF::CsectProperties(XCOFF::XMC_RW, XCOFF::XTY_SD)))
OutStreamer->emitXCOFFRefDirective("__llvm_prf_vnds[RW]");
}
}
void PPCAIXAsmPrinter::emitEndOfAsmFile(Module &M) {
// If there are no functions and there are no toc-data definitions in this
// module, we will never need to reference the TOC base.
if (M.empty() && TOCDataGlobalVars.empty())
return;
emitPGORefs();
// Switch to section to emit TOC base.
OutStreamer->SwitchSection(getObjFileLowering().getTOCBaseSection());

82
llvm/test/CodeGen/PowerPC/pgo-ref-directive.ll Normal file
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@ -0,0 +1,82 @@
; RUN: rm -rf %t && split-file %s %t
; RUN: llc -verify-machineinstrs -mcpu=pwr4 -mattr=-altivec -mtriple powerpc-ibm-aix-xcoff -xcoff-traceback-table=false < %t/no-ref.ll | FileCheck %s --check-prefixes=NOREF
; RUN: llc -verify-machineinstrs -mcpu=pwr4 -mattr=-altivec -mtriple powerpc-ibm-aix-xcoff -xcoff-traceback-table=false < %t/no-vnds.ll | FileCheck %s --check-prefixes=NOVNDS
; RUN: llc -verify-machineinstrs -mcpu=pwr4 -mattr=-altivec -mtriple powerpc-ibm-aix-xcoff -xcoff-traceback-table=false < %t/with-vnds.ll | FileCheck %s --check-prefixes=WITHVNDS
;--- no-ref.ll
; The absence of a __llvm_prf_cnts section should stop generating the .refs.
;
target datalayout = "E-m:a-p:32:32-i64:64-n32"
target triple = "powerpc-ibm-aix7.2.0.0"
@__profd_main = private global i64 zeroinitializer, section "__llvm_prf_data", align 8
@__llvm_prf_nm = private constant [6 x i8] c"\04\00main", section "__llvm_prf_names", align 1
@llvm.used = appending global [2 x i8*]
[i8* bitcast (i64* @__profd_main to i8*),
i8* getelementptr inbounds ([6 x i8], [6 x i8]* @__llvm_prf_nm, i32 0, i32 0)], section "llvm.metadata"
define i32 @main() #0 {
entry:
ret i32 1
}
; NOREF-NOT: .ref __llvm_prf_data
; NOREF-NOT: .ref __llvm_prf_names
; NOREF-NOT: .ref __llvm_prf_vnds
;--- no-vnds.ll
; This is the most common case. When -fprofile-generate is used and there exists executable code, we generate the __llvm_prf_cnts, __llvm_prf_data, and __llvm_prf_names sections.
;
target datalayout = "E-m:a-p:32:32-i64:64-n32"
target triple = "powerpc-ibm-aix7.2.0.0"
@__profc_main = private global [1 x i64] zeroinitializer, section "__llvm_prf_cnts", align 8
@__profd_main = private global i64 zeroinitializer, section "__llvm_prf_data", align 8
@__llvm_prf_nm = private constant [6 x i8] c"\04\00main", section "__llvm_prf_names", align 1
@llvm.used = appending global [3 x i8*]
[i8* bitcast ([1 x i64]* @__profc_main to i8*),
i8* bitcast (i64* @__profd_main to i8*),
i8* getelementptr inbounds ([6 x i8], [6 x i8]* @__llvm_prf_nm, i32 0, i32 0)], section "llvm.metadata"
define i32 @main() #0 {
entry:
ret i32 1
}
; There will be two __llvm_prf_cnts .csects, one to represent the actual csect
; that holds @__profc_main, and one generated to hold the .ref directives. In
; XCOFF, a csect can be defined in pieces, so this is is legal assembly.
;
; NOVNDS: .csect __llvm_prf_cnts[RW],3
; NOVNDS: .csect __llvm_prf_cnts[RW],3
; NOVNDS-NEXT: .ref __llvm_prf_data[RW]
; NOVNDS-NEXT: .ref __llvm_prf_names[RO]
; NOVNDS-NOT: .ref __llvm_prf_vnds
;--- with-vnds.ll
; When value profiling is needed, the PGO instrumentation generates variables in the __llvm_prf_vnds section, so we generate a .ref for them too.
;
@__profc_main = private global [1 x i64] zeroinitializer, section "__llvm_prf_cnts", align 8
@__profd_main = private global i64 zeroinitializer, section "__llvm_prf_data", align 8
@__llvm_prf_nm = private constant [6 x i8] c"\04\00main", section "__llvm_prf_names", align 1
@__llvm_prf_vnodes = private global [10 x { i64, i64, i8* }] zeroinitializer, section "__llvm_prf_vnds"
@llvm.used = appending global [4 x i8*]
[i8* bitcast ([1 x i64]* @__profc_main to i8*),
i8* bitcast (i64* @__profd_main to i8*),
i8* getelementptr inbounds ([6 x i8], [6 x i8]* @__llvm_prf_nm, i32 0, i32 0),
i8* bitcast ([10 x { i64, i64, i8* }]* @__llvm_prf_vnodes to i8*)], section "llvm.metadata"
define i32 @main() #0 {
entry:
ret i32 1
}
; WITHVNDS: .csect __llvm_prf_cnts[RW],3
; WITHVNDS: .csect __llvm_prf_cnts[RW],3
; WITHVNDS-NEXT: .ref __llvm_prf_data[RW]
; WITHVNDS-NEXT: .ref __llvm_prf_names[RO]
; WITHVNDS-NEXT: .ref __llvm_prf_vnds[RW]