[MachineCopyPropagation] Make a SmallVector larger (NFC)

[kazutakahirata]

This patch makes a SmallVector slightly larger. We encounter quite a
few instructions with 3 or 4 defs but very few beyond that on X86.

This saves 0.39% of heap allocations during the compilation of a large
preprocessed file, namely X86ISelLowering.cpp, for the X86 target.

[llvmbot]

@llvm/pr-subscribers-llvm-regalloc

Author: Kazu Hirata (kazutakahirata)

Changes

This patch makes a SmallVector slightly larger. We encounter quite a
few instructions with 3 or 4 defs but very few beyond that on X86.

This saves 0.39% of heap allocations during the compilation of a large
preprocessed file, namely X86ISelLowering.cpp, for the X86 target.

---

Full diff: https://github.com/llvm/llvm-project/pull/79106.diff

1 Files Affected:

• (modified) llvm/lib/CodeGen/MachineCopyPropagation.cpp (+1-1)

diff --git a/llvm/lib/CodeGen/MachineCopyPropagation.cpp b/llvm/lib/CodeGen/MachineCopyPropagation.cpp
index 51e944d0279f27..9a0ab300b21b7a 100644
--- a/llvm/lib/CodeGen/MachineCopyPropagation.cpp
+++ b/llvm/lib/CodeGen/MachineCopyPropagation.cpp
@@ -853,7 +853,7 @@ void MachineCopyPropagation::ForwardCopyPropagateBlock(MachineBasicBlock &MBB) {
     forwardUses(MI);
 
     // Not a copy.
-    SmallVector<Register, 2> Defs;
+    SmallVector<Register, 4> Defs;
     const MachineOperand *RegMask = nullptr;
     for (const MachineOperand &MO : MI.operands()) {
       if (MO.isRegMask())

[nikic]

LGTM