[Analysis] Restore the call to reserve

[kazutakahirata]

commit 47d8fec
Author: Kazu Hirata kazu@google.com
Date: Wed Apr 16 19:30:01 2025 -0700

has removed the call to reserve here. This patch restores it as
std::vector::insert, called by llvm::append_range, may not be able to
deduce the size of the range. For example, std::vector in libc++
distinguishes has two versions of std::vector::insert depending on
whether the iterator is an input iterator or a foward iterator.

[llvmbot]

@llvm/pr-subscribers-llvm-analysis

Author: Kazu Hirata (kazutakahirata)

Changes

commit 47d8fec
Author: Kazu Hirata <kazu@google.com>
Date: Wed Apr 16 19:30:01 2025 -0700

has removed the call to reserve here. This patch restores it as
std::vector::insert, called by llvm::append_range, may not be able to
deduce the size of the range. For example, std::vector in libc++
distinguishes has two versions of std::vector::insert depending on
whether the iterator is an input iterator or a foward iterator.

---

Full diff: https://github.com/llvm/llvm-project/pull/136215.diff

1 Files Affected:

• (modified) llvm/include/llvm/Analysis/BlockFrequencyInfoImpl.h (+1)

diff --git a/llvm/include/llvm/Analysis/BlockFrequencyInfoImpl.h b/llvm/include/llvm/Analysis/BlockFrequencyInfoImpl.h
index 57c408968b19a..2237f105e328b 100644
--- a/llvm/include/llvm/Analysis/BlockFrequencyInfoImpl.h
+++ b/llvm/include/llvm/Analysis/BlockFrequencyInfoImpl.h
@@ -1159,6 +1159,7 @@ void BlockFrequencyInfoImpl<BT>::setBlockFreq(const BlockT *BB,
 
 template <class BT> void BlockFrequencyInfoImpl<BT>::initializeRPOT() {
   const BlockT *Entry = &F->front();
+  RPOT.reserve(F->size());
   llvm::append_range(RPOT, post_order(Entry));
   std::reverse(RPOT.begin(), RPOT.end());