[llvm] 4ad8952 - [CodeGen][BasicBlockSections] Fix wrong alignment directive placement in
Sinan Lin via llvm-commits
llvm-commits at lists.llvm.org
Wed Nov 16 23:02:38 PST 2022
Author: Sinan Lin
Date: 2022-11-17T15:01:57+08:00
New Revision: 4ad8952d2d89243c776a40039dc4d54c8cd43e8d
URL: https://github.com/llvm/llvm-project/commit/4ad8952d2d89243c776a40039dc4d54c8cd43e8d
DIFF: https://github.com/llvm/llvm-project/commit/4ad8952d2d89243c776a40039dc4d54c8cd43e8d.diff
LOG: [CodeGen][BasicBlockSections] Fix wrong alignment directive placement in
basic block section cases
MachineBlockPlacement pass sets an alignment attribute to the loop
header MBB and this attribute will lead to an alignment directive during
emitting asm. In the case of the basic block section, the alignment
directive is put before the section label, and thus the alignment is set
to the predecessor of the loop header, which is not what we expect and
increases the code size (both inserting nop and set section alignment).
Reviewed By: rahmanl
Differential Revision: https://reviews.llvm.org/D137535
Added:
llvm/test/CodeGen/X86/align-basic-block-sections.mir
Modified:
llvm/lib/CodeGen/AsmPrinter/AsmPrinter.cpp
Removed:
################################################################################
diff --git a/llvm/lib/CodeGen/AsmPrinter/AsmPrinter.cpp b/llvm/lib/CodeGen/AsmPrinter/AsmPrinter.cpp
index 5863ce046c2a..10c0eea44f0d 100644
--- a/llvm/lib/CodeGen/AsmPrinter/AsmPrinter.cpp
+++ b/llvm/lib/CodeGen/AsmPrinter/AsmPrinter.cpp
@@ -3655,11 +3655,6 @@ void AsmPrinter::emitBasicBlockStart(const MachineBasicBlock &MBB) {
}
}
- // Emit an alignment directive for this block, if needed.
- const Align Alignment = MBB.getAlignment();
- if (Alignment != Align(1))
- emitAlignment(Alignment, nullptr, MBB.getMaxBytesForAlignment());
-
// Switch to a new section if this basic block must begin a section. The
// entry block is always placed in the function section and is handled
// separately.
@@ -3670,6 +3665,11 @@ void AsmPrinter::emitBasicBlockStart(const MachineBasicBlock &MBB) {
CurrentSectionBeginSym = MBB.getSymbol();
}
+ // Emit an alignment directive for this block, if needed.
+ const Align Alignment = MBB.getAlignment();
+ if (Alignment != Align(1))
+ emitAlignment(Alignment, nullptr, MBB.getMaxBytesForAlignment());
+
// If the block has its address taken, emit any labels that were used to
// reference the block. It is possible that there is more than one label
// here, because multiple LLVM BB's may have been RAUW'd to this block after
diff --git a/llvm/test/CodeGen/X86/align-basic-block-sections.mir b/llvm/test/CodeGen/X86/align-basic-block-sections.mir
new file mode 100644
index 000000000000..055a9dac5219
--- /dev/null
+++ b/llvm/test/CodeGen/X86/align-basic-block-sections.mir
@@ -0,0 +1,136 @@
+# Check if the alignment directive is put on the correct place when the basic block section option is used.
+# RUN: llc -start-after=bbsections-prepare %s -o - | FileCheck %s -check-prefix=CHECK
+
+# How to generate the input:
+# foo.c
+# int test(int a) {
+# switch (a) {
+# default:
+# return 10;
+# case 1:
+# a += 1;
+# case 2:
+# a *= -1;
+# case 8:
+# break;
+# }
+# return a;
+# }
+#
+# clang -O0 -S -emit-llvm test.c
+# llc < test.ll -stop-after=bbsections-prepare -align-all-nofallthru-blocks=8 -basic-block-sections=all
+
+
+--- |
+ define i32 @test(i32 noundef %a) {
+ entry:
+ switch i32 %a, label %return [
+ i32 1, label %sw.bb1
+ i32 2, label %sw.bb1
+ i32 8, label %sw.epilog
+ ]
+
+ sw.bb1: ; preds = %entry, %entry
+ br label %sw.epilog
+
+ sw.epilog: ; preds = %sw.bb1, %entry
+ %a.addr.1 = phi i32 [ %a, %entry ], [ -2, %sw.bb1 ]
+ br label %return
+
+ return: ; preds = %sw.epilog, %entry
+ %retval.0 = phi i32 [ %a.addr.1, %sw.epilog ], [ 10, %entry ]
+ ret i32 %retval.0
+ }
+
+
+...
+---
+name: test
+alignment: 16
+exposesReturnsTwice: false
+legalized: false
+regBankSelected: false
+selected: false
+failedISel: false
+tracksRegLiveness: true
+hasWinCFI: false
+callsEHReturn: false
+callsUnwindInit: false
+hasEHCatchret: false
+hasEHScopes: false
+hasEHFunclets: false
+failsVerification: false
+tracksDebugUserValues: true
+registers: []
+liveins:
+ - { reg: '$edi', virtual-reg: '' }
+frameInfo:
+ isFrameAddressTaken: false
+ isReturnAddressTaken: false
+ hasStackMap: false
+ hasPatchPoint: false
+ stackSize: 0
+ offsetAdjustment: 0
+ maxAlignment: 1
+ adjustsStack: false
+ hasCalls: false
+ stackProtector: ''
+ functionContext: ''
+ maxCallFrameSize: 0
+ cvBytesOfCalleeSavedRegisters: 0
+ hasOpaqueSPAdjustment: false
+ hasVAStart: false
+ hasMustTailInVarArgFunc: false
+ hasTailCall: false
+ localFrameSize: 0
+ savePoint: ''
+ restorePoint: ''
+fixedStack: []
+stack: []
+callSites: []
+debugValueSubstitutions: []
+constants: []
+machineFunctionInfo: {}
+body: |
+ bb.0.entry:
+ successors: %bb.1(0x40000000), %bb.2(0x40000000)
+ liveins: $edi
+
+ renamable $edi = KILL $edi, implicit-def $rdi
+ renamable $eax = LEA64_32r renamable $rdi, 1, $noreg, -1, $noreg
+ CMP32ri8 killed renamable $eax, 2, implicit-def $eflags
+ JCC_1 %bb.2, 3, implicit $eflags
+ JMP_1 %bb.1
+
+ bb.1.sw.bb1 (bbsections 1):
+ successors: %bb.3(0x80000000)
+
+ renamable $edi = MOV32ri -2, implicit-def $rdi
+ JMP_1 %bb.3
+
+ bb.2.entry (align 256, bbsections 2):
+ successors: %bb.3(0x40000000), %bb.4(0x40000000)
+ liveins: $rdi
+
+ renamable $eax = MOV32ri 10
+ CMP32ri8 renamable $edi, 8, implicit-def $eflags
+ JCC_1 %bb.4, 5, implicit $eflags
+ JMP_1 %bb.3
+
+ bb.3.sw.epilog (bbsections 3):
+ successors: %bb.4(0x80000000)
+ liveins: $rdi
+
+ $eax = MOV32rr $edi, implicit killed $rdi
+ JMP_1 %bb.4
+
+ bb.4.return (bbsections 4):
+ liveins: $eax
+
+ RET64 $eax
+
+...
+
+# CHECK: .section .text.test,"ax", at progbits,unique,2
+# CHECK-NEXT: .p2align 8, 0x90
+# CHECK-NEXT: test.__part.2: # %entry
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