[llvm] [BasicBlockSections] Always keep the entry block in the beginning of the function. (PR #74696)
Rahman Lavaee via llvm-commits
llvm-commits at lists.llvm.org
Tue Jan 16 13:30:03 PST 2024
https://github.com/rlavaee updated https://github.com/llvm/llvm-project/pull/74696
>From 967e08bf6d59444a257d77c057069d80781095c8 Mon Sep 17 00:00:00 2001
From: Rahman Lavaee <rahmanl at google.com>
Date: Wed, 6 Dec 2023 23:17:39 +0000
Subject: [PATCH] [BasicBlockSections] Always keep the entry block in the
beginning of the function.
BasicBlockSections must enforce placing the entry block at the beginning
of the function regardless of the basic block sections profile.
---
llvm/include/llvm/CodeGen/MachineBasicBlock.h | 4 +-
llvm/lib/CodeGen/BasicBlockSections.cpp | 10 +++--
.../BasicBlockSectionsProfileReader.cpp | 7 ---
.../basic-block-sections-clusters-error.ll | 6 +--
.../X86/basic-block-sections-entryblock.ll | 43 +++++++++++++++++++
5 files changed, 53 insertions(+), 17 deletions(-)
create mode 100644 llvm/test/CodeGen/X86/basic-block-sections-entryblock.ll
diff --git a/llvm/include/llvm/CodeGen/MachineBasicBlock.h b/llvm/include/llvm/CodeGen/MachineBasicBlock.h
index 5812295f73b5a2e..c84fd281c6a549b 100644
--- a/llvm/include/llvm/CodeGen/MachineBasicBlock.h
+++ b/llvm/include/llvm/CodeGen/MachineBasicBlock.h
@@ -74,10 +74,10 @@ struct MBBSectionID {
MBBSectionID(SectionType T) : Type(T), Number(0) {}
};
-// This structure represents the information for a basic block.
+// This structure represents the information for a basic block pertaining to
+// the basic block sections profile.
struct UniqueBBID {
unsigned BaseID;
- // sections profile).
unsigned CloneID;
};
diff --git a/llvm/lib/CodeGen/BasicBlockSections.cpp b/llvm/lib/CodeGen/BasicBlockSections.cpp
index 94b5a503fbd0f3e..fbc37de2fbacf23 100644
--- a/llvm/lib/CodeGen/BasicBlockSections.cpp
+++ b/llvm/lib/CodeGen/BasicBlockSections.cpp
@@ -318,9 +318,8 @@ bool BasicBlockSections::runOnMachineFunction(MachineFunction &MF) {
MF.setBBSectionsType(BBSectionsType);
assignSections(MF, FuncClusterInfo);
- // We make sure that the cluster including the entry basic block precedes all
- // other clusters.
- auto EntryBBSectionID = MF.front().getSectionID();
+ const MachineBasicBlock &EntryBB = MF.front();
+ auto EntryBBSectionID = EntryBB.getSectionID();
// Helper function for ordering BB sections as follows:
// * Entry section (section including the entry block).
@@ -341,12 +340,17 @@ bool BasicBlockSections::runOnMachineFunction(MachineFunction &MF) {
// contiguous and ordered accordingly. Furthermore, clusters are ordered in
// increasing order of their section IDs, with the exception and the
// cold section placed at the end of the function.
+ // Also, we force the entry block of the function to be placed at the
+ // beginning of the function, regardless of requested order.
auto Comparator = [&](const MachineBasicBlock &X,
const MachineBasicBlock &Y) {
auto XSectionID = X.getSectionID();
auto YSectionID = Y.getSectionID();
if (XSectionID != YSectionID)
return MBBSectionOrder(XSectionID, YSectionID);
+ // Make sure that the entry block is placed at the beginning.
+ if (&X == &EntryBB || &Y == &EntryBB)
+ return &X == &EntryBB;
// If the two basic block are in the same section, the order is decided by
// their position within the section.
if (XSectionID.Type == MBBSectionID::SectionType::Default)
diff --git a/llvm/lib/CodeGen/BasicBlockSectionsProfileReader.cpp b/llvm/lib/CodeGen/BasicBlockSectionsProfileReader.cpp
index 79e42d9304dfe34..6eef5d2c50a2f98 100644
--- a/llvm/lib/CodeGen/BasicBlockSectionsProfileReader.cpp
+++ b/llvm/lib/CodeGen/BasicBlockSectionsProfileReader.cpp
@@ -214,10 +214,6 @@ Error BasicBlockSectionsProfileReader::ReadV1Profile() {
Twine("duplicate basic block id found '") + BasicBlockIDStr +
"'");
- if (!BasicBlockID->BaseID && CurrentPosition)
- return createProfileParseError(
- "entry BB (0) does not begin a cluster.");
-
FI->second.ClusterInfo.emplace_back(BBClusterInfo{
*std::move(BasicBlockID), CurrentCluster, CurrentPosition++});
}
@@ -288,9 +284,6 @@ Error BasicBlockSectionsProfileReader::ReadV0Profile() {
if (!FuncBBIDs.insert(BBID).second)
return createProfileParseError(
Twine("duplicate basic block id found '") + BBIDStr + "'");
- if (BBID == 0 && CurrentPosition)
- return createProfileParseError(
- "entry BB (0) does not begin a cluster");
FI->second.ClusterInfo.emplace_back(
BBClusterInfo({{static_cast<unsigned>(BBID), 0},
diff --git a/llvm/test/CodeGen/X86/basic-block-sections-clusters-error.ll b/llvm/test/CodeGen/X86/basic-block-sections-clusters-error.ll
index 597d8f6707ecca3..d6f3d5010b55673 100644
--- a/llvm/test/CodeGen/X86/basic-block-sections-clusters-error.ll
+++ b/llvm/test/CodeGen/X86/basic-block-sections-clusters-error.ll
@@ -5,10 +5,6 @@
; RUN: echo '!!1' >> %t1
; RUN: not --crash llc < %s -O0 -mtriple=x86_64-pc-linux -function-sections -basic-block-sections=%t1 2>&1 | FileCheck %s --check-prefix=CHECK-ERROR1
; CHECK-ERROR1: LLVM ERROR: invalid profile {{.*}} at line 3: duplicate basic block id found '1'
-; RUN: echo '!dummy1' > %t2
-; RUN: echo '!!4 0' >> %t2
-; RUN: not --crash llc < %s -O0 -mtriple=x86_64-pc-linux -function-sections -basic-block-sections=%t2 2>&1 | FileCheck %s --check-prefix=CHECK-ERROR2
-; CHECK-ERROR2: LLVM ERROR: invalid profile {{.*}} at line 2: entry BB (0) does not begin a cluster
; RUN: echo '!dummy1' > %t3
; RUN: echo '!!-1' >> %t3
; RUN: not --crash llc < %s -O0 -mtriple=x86_64-pc-linux -function-sections -basic-block-sections=%t3 2>&1 | FileCheck %s --check-prefix=CHECK-ERROR3
@@ -48,7 +44,7 @@
; RUN: echo 'f dummy1' >> %t11
; RUN: echo 'c 0 1.a' >> %t11
; RUN: not --crash llc < %s -O0 -mtriple=x86_64 -function-sections -basic-block-sections=%t11 2>&1 | FileCheck %s --check-prefix=CHECK-ERROR11
-; CHECK-ERROR11: LLVM ERROR: invalid profile {{.*}} at line 3: unable to parse clone id: 'a'
+; CHECK-ERROR11: LLVM ERROR: invalid profile {{.*}} at line 3: unable to parse clone id: 'a'
; RUN: echo 'v1' > %t12
; RUN: echo 'f dummy1' >> %t12
; RUN: echo 'c 0 1' >> %t12
diff --git a/llvm/test/CodeGen/X86/basic-block-sections-entryblock.ll b/llvm/test/CodeGen/X86/basic-block-sections-entryblock.ll
new file mode 100644
index 000000000000000..349015e1403df90
--- /dev/null
+++ b/llvm/test/CodeGen/X86/basic-block-sections-entryblock.ll
@@ -0,0 +1,43 @@
+; COM: Tests to verify that the entry basic block is always placed at the beginning of its section.
+; RUN: echo 'v1' > %t1
+; RUN: echo 'f foo' >> %t1
+; RUN: echo 'c2 0' >> %t1
+; RUN: llc < %s -mtriple=x86_64-pc-linux -function-sections -basic-block-sections=%t1 -O0 | FileCheck %s -check-prefix=LINUX-SECTIONS1
+
+; RUN: echo 'v1' > %t2
+; RUN: echo 'f foo' >> %t2
+; RUN: echo 'c2' >> %t2
+; RUN: llc < %s -mtriple=x86_64-pc-linux -function-sections -basic-block-sections=%t2 -O0 | FileCheck %s -check-prefix=LINUX-SECTIONS2
+
+
+define void @foo(i1 %a, i1 %b) {
+b0:
+ br i1 %a, label %b1, label %b2
+
+b1: ; preds = %b0
+ ret void
+
+b2: ; preds = %b0
+ ret void
+}
+
+;; Check that %b0 is emitted at the beginning of the function.
+; LINUX-SECTIONS1: .section .text.foo,"ax", at progbits
+; LINUX-SECTIONS1: foo:
+; LINUX-SECTIONS1: # %bb.0: # %b0
+; LINUX-SECTIONS1: jne foo.cold
+; LINUX-SECTIONS1: # %bb.2: # %b2
+; LINUX-SECTIONS1: retq
+; LINUX-SECTIONS1: .section .text.split.foo,"ax", at progbits
+; LINUX-SECTIONS1: foo.cold: # %b1
+; LINUX-SECTIONS1: retq
+
+; LINUX-SECTIONS2: .section .text.foo,"ax", at progbits
+; LINUX-SECTIONS2: foo:
+; LINUX-SECTIONS2: # %bb.0: # %b0
+; LINUX-SECTIONS2: je foo.__part.0
+; LINUX-SECTIONS2: # %bb.1: # %b1
+; LINUX-SECTIONS2: retq
+; LINUX-SECTIONS2: .section .text.foo,"ax", at progbits
+; LINUX-SECTIONS2: foo.__part.0: # %b2
+; LINUX-SECTIONS2: retq
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