[CodeGen] Use SmallVector for MBB preds/succs

[aengelke]

Avoid extra heap allocations for typical predecessor/successor counts.

c-t-t -0.14% stage2-O0-g

[llvmbot]

@llvm/pr-subscribers-pgo
@llvm/pr-subscribers-llvm-analysis

@llvm/pr-subscribers-backend-hexagon

Author: Alexis Engelke (aengelke)

Changes

Avoid extra heap allocations for typical predecessor/successor counts.

c-t-t -0.14% stage2-O0-g

---

Full diff: https://github.com/llvm/llvm-project/pull/101948.diff

3 Files Affected:

• (modified) llvm/include/llvm/Analysis/RegionInfoImpl.h (+1-1)
• (modified) llvm/include/llvm/CodeGen/MachineBasicBlock.h (+12-10)
• (modified) llvm/lib/Target/Hexagon/HexagonCopyHoisting.cpp (+1-1)

diff --git a/llvm/include/llvm/Analysis/RegionInfoImpl.h b/llvm/include/llvm/Analysis/RegionInfoImpl.h
index c5e8821858fd2..2ea432ea95d37 100644
--- a/llvm/include/llvm/Analysis/RegionInfoImpl.h
+++ b/llvm/include/llvm/Analysis/RegionInfoImpl.h
@@ -814,7 +814,7 @@ RegionInfoBase<Tr>::getMaxRegionExit(BlockT *BB) const {
     // Get the single exit of BB.
     if (R && R->getEntry() == BB)
       Exit = R->getExit();
-    else if (++BlockTraits::child_begin(BB) == BlockTraits::child_end(BB))
+    else if (BlockTraits::child_begin(BB) + 1 == BlockTraits::child_end(BB))
       Exit = *BlockTraits::child_begin(BB);
     else // No single exit exists.
       return Exit;
diff --git a/llvm/include/llvm/CodeGen/MachineBasicBlock.h b/llvm/include/llvm/CodeGen/MachineBasicBlock.h
index b8153fd5d3fb7..5b80827b780b5 100644
--- a/llvm/include/llvm/CodeGen/MachineBasicBlock.h
+++ b/llvm/include/llvm/CodeGen/MachineBasicBlock.h
@@ -157,8 +157,8 @@ class MachineBasicBlock
   Instructions Insts;
 
   /// Keep track of the predecessor / successor basic blocks.
-  std::vector<MachineBasicBlock *> Predecessors;
-  std::vector<MachineBasicBlock *> Successors;
+  SmallVector<MachineBasicBlock *, 4> Predecessors;
+  SmallVector<MachineBasicBlock *, 2> Successors;
 
   /// Keep track of the probabilities to the successors. This vector has the
   /// same order as Successors, or it is empty if we don't use it (disable
@@ -387,18 +387,20 @@ class MachineBasicBlock
   }
 
   // Machine-CFG iterators
-  using pred_iterator = std::vector<MachineBasicBlock *>::iterator;
-  using const_pred_iterator = std::vector<MachineBasicBlock *>::const_iterator;
-  using succ_iterator = std::vector<MachineBasicBlock *>::iterator;
-  using const_succ_iterator = std::vector<MachineBasicBlock *>::const_iterator;
+  using pred_iterator = SmallVectorImpl<MachineBasicBlock *>::iterator;
+  using const_pred_iterator =
+      SmallVectorImpl<MachineBasicBlock *>::const_iterator;
+  using succ_iterator = SmallVectorImpl<MachineBasicBlock *>::iterator;
+  using const_succ_iterator =
+      SmallVectorImpl<MachineBasicBlock *>::const_iterator;
   using pred_reverse_iterator =
-      std::vector<MachineBasicBlock *>::reverse_iterator;
+      SmallVectorImpl<MachineBasicBlock *>::reverse_iterator;
   using const_pred_reverse_iterator =
-      std::vector<MachineBasicBlock *>::const_reverse_iterator;
+      SmallVectorImpl<MachineBasicBlock *>::const_reverse_iterator;
   using succ_reverse_iterator =
-      std::vector<MachineBasicBlock *>::reverse_iterator;
+      SmallVectorImpl<MachineBasicBlock *>::reverse_iterator;
   using const_succ_reverse_iterator =
-      std::vector<MachineBasicBlock *>::const_reverse_iterator;
+      SmallVectorImpl<MachineBasicBlock *>::const_reverse_iterator;
   pred_iterator        pred_begin()       { return Predecessors.begin(); }
   const_pred_iterator  pred_begin() const { return Predecessors.begin(); }
   pred_iterator        pred_end()         { return Predecessors.end();   }
diff --git a/llvm/lib/Target/Hexagon/HexagonCopyHoisting.cpp b/llvm/lib/Target/Hexagon/HexagonCopyHoisting.cpp
index e9d95c6e89db4..a43042a303093 100644
--- a/llvm/lib/Target/Hexagon/HexagonCopyHoisting.cpp
+++ b/llvm/lib/Target/Hexagon/HexagonCopyHoisting.cpp
@@ -249,7 +249,7 @@ void HexagonCopyHoisting::moveCopyInstr(MachineBasicBlock *DestBB,
   DestBB->splice(FirstTI, MI->getParent(), MI);
 
   addMItoCopyList(MI);
-  for (auto I = ++(DestBB->succ_begin()), E = DestBB->succ_end(); I != E; ++I) {
+  for (auto I = DestBB->succ_begin() + 1, E = DestBB->succ_end(); I != E; ++I) {
     MachineBasicBlock *SuccBB = *I;
     auto &BBCopyInst = CopyMIList[SuccBB->getNumber()];
     MachineInstr *SuccMI = BBCopyInst[Key];

[nikic]

sccache C:\BuildTools\VC\Tools\MSVC\14.29.30133\bin\Hostx64\x64\cl.exe  /nologo /TP -DBUILD_EXAMPLES -DGTEST_HAS_RTTI=0 -DUNICODE -D_CRT_NONSTDC_NO_DEPRECATE -D_CRT_NONSTDC_NO_WARNINGS -D_CRT_SECURE_NO_DEPRECATE -D_CRT_SECURE_NO_WARNINGS -D_GLIBCXX_ASSERTIONS -D_HAS_EXCEPTIONS=0 -D_SCL_SECURE_NO_DEPRECATE -D_SCL_SECURE_NO_WARNINGS -D_UNICODE -D__STDC_CONSTANT_MACROS -D__STDC_FORMAT_MACROS -D__STDC_LIMIT_MACROS -Ilib\CodeGen -IC:\ws\src\llvm\lib\CodeGen -Iinclude -IC:\ws\src\llvm\include /DWIN32 /D_WINDOWS   /Zc:inline /Zc:preprocessor /Zc:__cplusplus /Oi /bigobj /permissive- /W4 -wd4141 -wd4146 -wd4244 -wd4267 -wd4291 -wd4351 -wd4456 -wd4457 -wd4458 -wd4459 -wd4503 -wd4624 -wd4722 -wd4100 -wd4127 -wd4512 -wd4505 -wd4610 -wd4510 -wd4702 -wd4245 -wd4706 -wd4310 -wd4701 -wd4703 -wd4389 -wd4611 -wd4805 -wd4204 -wd4577 -wd4091 -wd4592 -wd4319 -wd4709 -wd5105 -wd4324 -w14062 -we4238 /Gw /O2 /Ob2  -MD  /EHs-c- /GR- -UNDEBUG -std:c++17 /showIncludes /Folib\CodeGen\CMakeFiles\LLVMCodeGen.dir\MIRSampleProfile.cpp.obj /Fdlib\CodeGen\CMakeFiles\LLVMCodeGen.dir\LLVMCodeGen.pdb /FS -c C:\ws\src\llvm\lib\CodeGen\MIRSampleProfile.cpp
C:\ws\src\llvm\lib\CodeGen\MIRSampleProfile.cpp(136): error C2440: 'return': cannot convert from 'llvm::iterator_range<llvm::MachineBasicBlock::pred_iterator>' to 'llvm::iterator_range<std::_Vector_iterator<std::_Vector_val<std::_Simple_types<_Ty>>>>'
        with
        [
            _Ty=llvm::MachineBasicBlock *
        ]
C:\ws\src\llvm\lib\CodeGen\MIRSampleProfile.cpp(136): note: No user-defined-conversion operator available that can perform this conversion, or the operator cannot be called
C:\ws\src\llvm\lib\CodeGen\MIRSampleProfile.cpp(139): error C2440: 'return': cannot convert from 'llvm::iterator_range<llvm::MachineBasicBlock::pred_iterator>' to 'llvm::iterator_range<std::_Vector_iterator<std::_Vector_val<std::_Simple_types<_Ty>>>>'
        with
        [
            _Ty=llvm::MachineBasicBlock *
        ]
C:\ws\src\llvm\lib\CodeGen\MIRSampleProfile.cpp(139): note: No user-defined-conversion operator available that can perform this conversion, or the operator cannot be called

[nikic]

Use std::next() to make this independent of implementation details?

[arsenm]

I'm surprised this wasn't already the case

[nikic]

LGTM