Improve perf with `-separate-debug-info` (#8670)

When Slang form a new spirv code without the debug info, List container
had to reserve the memory space before adding items in it.

This improves the given repro test time from 56 minutes to 6 minutes.

1 files changed, 14 insertions, 3 deletions

diff --git a/source/slang/slang-emit.cpp b/source/slang/slang-emit.cpp
index c57851bc2..1bd1f8b5c 100644
--- a/source/slang/slang-emit.cpp
+++ b/source/slang/slang-emit.cpp
@@ -2342,6 +2342,10 @@ public:
     // we can read.
     SlangResult loadBlob(ComPtr<IArtifact>& artifact)
     {
+        m_nonSemanticDebugInfoExtSetId = 0;
+        m_words.clear();
+        m_headerWords.clear();
+
         ComPtr<ISlangBlob> spirvBlob;
         SlangResult res = artifact->loadBlob(ArtifactKeep::Yes, spirvBlob.writeRef());
         if (SLANG_FAILED(res) || !spirvBlob ||
@@ -2349,7 +2353,6 @@ public:
             return SLANG_FAIL;
 
         // Populate the full array of SPIR-V words.
-        m_words.clear();
         m_words.addRange(
             reinterpret_cast<const SpvWord*>(spirvBlob->getBufferPointer()),
             spirvBlob->getBufferSize() / sizeof(SpvWord));
@@ -2363,7 +2366,9 @@ public:
     }
 
     // Get the header words.
-    List<SpvWord> getHeaderWords() const { return m_headerWords; }
+    const List<SpvWord>& getHeaderWords() const { return m_headerWords; }
+
+    Index getWordCount() const { return m_words.getCount(); }
 
     // Visit all SPIRV instructions (excluding header words), invoking the callback for each
     // instruction. The callback should be a function or lambda with signature: void(const
@@ -2457,9 +2462,15 @@ static SlangResult stripDbgSpirvFromArtifact(
     SpirvInstructionHelper spirvInstructionHelper;
     SLANG_RETURN_ON_FAIL(spirvInstructionHelper.loadBlob(artifact));
 
-    auto headerWords = spirvInstructionHelper.getHeaderWords();
+    const auto& headerWords = spirvInstructionHelper.getHeaderWords();
 
     List<uint8_t> spirvWordsList;
+    if (auto totalWordCapacity = headerWords.getCount() + spirvInstructionHelper.getWordCount())
+    {
+        const Index byteCapacity = totalWordCapacity * sizeof(SpvWord);
+        spirvWordsList.reserve(byteCapacity);
+    }
+
     spirvWordsList.addRange(
         reinterpret_cast<const uint8_t*>(headerWords.getBuffer()),
         headerWords.getCount() * sizeof(SpvWord));