[SHT_LLVM_BB_ADDR_MAP] Allow basic-block-sections and labels be used together by decoupling the handling of the two features. (#74128)
Today `-split-machine-functions` and `-fbasic-block-sections={all,list}`
cannot be combined with `-basic-block-sections=labels` (the labels
option will be ignored).
The inconsistency comes from the way basic block address map -- the
underlying mechanism for basic block labels -- encodes basic block
addresses
(https://lists.llvm.org/pipermail/llvm-dev/2020-July/143512.html).
Specifically, basic block offsets are computed relative to the function
begin symbol. This relies on functions being contiguous which is not the
case for MFS and basic block section binaries. This means Propeller
cannot use binary profiles collected from these binaries, which limits
the applicability of Propeller for iterative optimization.
To make the `SHT_LLVM_BB_ADDR_MAP` feature work with basic block section
binaries, we propose modifying the encoding of this section as follows.
First let us review the current encoding which emits the address of each
function and its number of basic blocks, followed by basic block entries
for each basic block.
| | |
|--|--|
| Address of the function | Function Address |
| Number of basic blocks in this function | NumBlocks |
| BB entry 1
| BB entry 2
| ...
| BB entry #NumBlocks
To make this work for basic block sections, we treat each basic block
section similar to a function, except that basic block sections of the
same function must be encapsulated in the same structure so we can map
all of them to their single function.
We modify the encoding to first emit the number of basic block sections
(BB ranges) in the function. Then we emit the address map of each basic
block section section as before: the base address of the section, its
number of blocks, and BB entries for its basic block. The first section
in the BB address map is always the function entry section.
| | |
|--|--|
| Number of sections for this function | NumBBRanges |
| Section 1 begin address | BaseAddress[1] |
| Number of basic blocks in section 1 | NumBlocks[1] |
| BB entries for Section 1
|..................|
| Section #NumBBRanges begin address | BaseAddress[NumBBRanges] |
| Number of basic blocks in section #NumBBRanges |
NumBlocks[NumBBRanges] |
| BB entries for Section #NumBBRanges
The encoding of basic block entries remains as before with the minor
change that each basic block offset is now computed relative to the
begin symbol of its containing BB section.
This patch adds a new boolean codegen option `-basic-block-address-map`.
Correspondingly, the front-end flag `-fbasic-block-address-map` and LLD
flag `--lto-basic-block-address-map` are introduced.
Analogously, we add a new TargetOption field `BBAddrMap`. This means BB
address maps are either generated for all functions in the compiling
unit, or for none (depending on `TargetOptions::BBAddrMap`).
This patch keeps the functionality of the old
`-fbasic-block-sections=labels` option but does not remove it. A
subsequent patch will remove the obsolete option.
We refactor the `BasicBlockSections` pass by separating the BB address
map and BB sections handing to their own functions (named
`handleBBAddrMap` and `handleBBSections`). `handleBBSections` renumbers
basic blocks and places them in their assigned sections.
`handleBBAddrMap` is invoked after `handleBBSections` (if requested) and
only renumbers the blocks.
- New tests added:
- Two tests basic-block-address-map-with-basic-block-sections.ll and
basic-block-address-map-with-mfs.ll to exercise the combination of
`-basic-block-address-map` with `-basic-block-sections=list` and
'-split-machine-functions`.
- A driver sanity test for the `-fbasic-block-address-map` option
(basic-block-address-map.c).
- An LLD test for testing the `--lto-basic-block-address-map` option.
This reuses the LLVM IR from `lld/test/ELF/lto/basic-block-sections.ll`.
- Renamed and modified the two existing codegen tests for basic block
address map (`basic-block-sections-labels-functions-sections.ll` and
`basic-block-sections-labels.ll`)
- Removed `SHT_LLVM_BB_ADDR_MAP_V0` tests. Full deprecation of
`SHT_LLVM_BB_ADDR_MAP_V0` and `SHT_LLVM_BB_ADDR_MAP` version less than 2
will happen in a separate PR in a few months.
GitOrigin-RevId: acec6419e811a46050b0603dfa72fc6a169aa0f7
diff --git a/ELF/Config.h b/ELF/Config.h
index 3a4a47d..fcca8c4 100644
--- a/ELF/Config.h
+++ b/ELF/Config.h
@@ -187,6 +187,7 @@
llvm::StringRef cmseOutputLib;
StringRef zBtiReport = "none";
StringRef zCetReport = "none";
+ bool ltoBBAddrMap;
llvm::StringRef ltoBasicBlockSections;
std::pair<llvm::StringRef, llvm::StringRef> thinLTOObjectSuffixReplace;
llvm::StringRef thinLTOPrefixReplaceOld;
diff --git a/ELF/Driver.cpp b/ELF/Driver.cpp
index f4b7d1c..c19fba6 100644
--- a/ELF/Driver.cpp
+++ b/ELF/Driver.cpp
@@ -1298,6 +1298,9 @@
config->ltoObjPath = args.getLastArgValue(OPT_lto_obj_path_eq);
config->ltoPartitions = args::getInteger(args, OPT_lto_partitions, 1);
config->ltoSampleProfile = args.getLastArgValue(OPT_lto_sample_profile);
+ config->ltoBBAddrMap =
+ args.hasFlag(OPT_lto_basic_block_address_map,
+ OPT_no_lto_basic_block_address_map, false);
config->ltoBasicBlockSections =
args.getLastArgValue(OPT_lto_basic_block_sections);
config->ltoUniqueBasicBlockSectionNames =
diff --git a/ELF/LTO.cpp b/ELF/LTO.cpp
index c39c6e6..3d92007 100644
--- a/ELF/LTO.cpp
+++ b/ELF/LTO.cpp
@@ -61,6 +61,8 @@
c.Options.FunctionSections = true;
c.Options.DataSections = true;
+ c.Options.BBAddrMap = config->ltoBBAddrMap;
+
// Check if basic block sections must be used.
// Allowed values for --lto-basic-block-sections are "all", "labels",
// "<file name specifying basic block ids>", or none. This is the equivalent
diff --git a/ELF/Options.td b/ELF/Options.td
index c2c9cab..c10a73e 100644
--- a/ELF/Options.td
+++ b/ELF/Options.td
@@ -637,6 +637,9 @@
Values<"resolution,preopt,promote,internalize,import,opt,precodegen,prelink,combinedindex">;
def lto_basic_block_sections: JJ<"lto-basic-block-sections=">,
HelpText<"Enable basic block sections for LTO">;
+defm lto_basic_block_address_map: BB<"lto-basic-block-address-map",
+ "Emit basic block address map for LTO",
+ "Do not emit basic block address map for LTO (default)">;
defm lto_unique_basic_block_section_names: BB<"lto-unique-basic-block-section-names",
"Give unique names to every basic block section for LTO",
"Do not give unique names to every basic block section for LTO (default)">;
diff --git a/test/ELF/lto/basic-block-address-map.ll b/test/ELF/lto/basic-block-address-map.ll
new file mode 100644
index 0000000..b96e7a8
--- /dev/null
+++ b/test/ELF/lto/basic-block-address-map.ll
@@ -0,0 +1,28 @@
+; REQUIRES: x86
+; RUN: llvm-as %s -o %t.o
+; RUN: ld.lld %t.o -o %t --lto-basic-block-address-map --lto-O0 --save-temps
+; RUN: llvm-readobj --sections %t.lto.o | FileCheck --check-prefix=SECNAMES %s
+
+; SECNAMES: Type: SHT_LLVM_BB_ADDR_MAP
+
+target datalayout = "e-m:e-p270:32:32-p271:32:32-p272:64:64-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-unknown-linux-gnu"
+
+; Function Attrs: nounwind uwtable
+define dso_local void @foo(i32 %b) local_unnamed_addr {
+entry:
+ %tobool.not = icmp eq i32 %b, 0
+ br i1 %tobool.not, label %if.end, label %if.then
+
+if.then: ; preds = %entry
+ tail call void @foo(i32 0)
+ br label %if.end
+
+if.end: ; preds = %entry, %if.then
+ ret void
+}
+
+define void @_start() {
+ call void @foo(i32 1)
+ ret void
+}
