[clang] [clang][CodeGen] Omit pre-opt link when post-opt is link requested (PR #85672)

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llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-clang-codegen

Author: Jacob Lambert (lamb-j)

<details>
<summary>Changes</summary>

Currently, when the -relink-builtin-bitcodes-postop option is used we link builtin bitcodes twice: once before optimization, and again after optimization.

With this change, we omit the pre-opt linking when the option is set, and we rename the option to the following:

  -link-builtin-bitcodes-postopt

The goal of this change is to reduce compile time. We do lose the benefits of pre-opt linking, but we may be able to address this in a future patch by adjusting the position of the builtin-bitcode linking pass.

Compilations not setting the relink (link) option are unaffected

---
Full diff: https://github.com/llvm/llvm-project/pull/85672.diff


3 Files Affected:

- (modified) clang/lib/CodeGen/BackendUtil.cpp (+5-8) 
- (modified) clang/lib/CodeGen/CodeGenAction.cpp (+3-3) 
- (modified) clang/lib/CodeGen/LinkInModulesPass.cpp (-4) 


``````````diff
diff --git a/clang/lib/CodeGen/BackendUtil.cpp b/clang/lib/CodeGen/BackendUtil.cpp
index 82b30b8d815629..c5571eb15ce3a9 100644
--- a/clang/lib/CodeGen/BackendUtil.cpp
+++ b/clang/lib/CodeGen/BackendUtil.cpp
@@ -112,9 +112,9 @@ static cl::opt<bool> ClSanitizeOnOptimizerEarlyEP(
 extern cl::opt<InstrProfCorrelator::ProfCorrelatorKind> ProfileCorrelate;
 
 // Re-link builtin bitcodes after optimization
-cl::opt<bool> ClRelinkBuiltinBitcodePostop(
-    "relink-builtin-bitcode-postop", cl::Optional,
-    cl::desc("Re-link builtin bitcodes after optimization."), cl::init(false));
+cl::opt<bool> ClLinkBuiltinBitcodePostopt(
+    "link-builtin-bitcode-postopt", cl::Optional,
+    cl::desc("Link builtin bitcodes after optimization."), cl::init(false));
 } // namespace llvm
 
 namespace {
@@ -1051,11 +1051,8 @@ void EmitAssemblyHelper::RunOptimizationPipeline(
     }
   }
 
-  // Re-link against any bitcodes supplied via the -mlink-builtin-bitcode option
-  // Some optimizations may generate new function calls that would not have
-  // been linked pre-optimization (i.e. fused sincos calls generated by
-  // AMDGPULibCalls::fold_sincos.)
-  if (ClRelinkBuiltinBitcodePostop)
+  // Link against bitcodes supplied via the -mlink-builtin-bitcode option
+  if (ClLinkBuiltinBitcodePostopt)
     MPM.addPass(LinkInModulesPass(BC, false));
 
   // Add a verifier pass if requested. We don't have to do this if the action
diff --git a/clang/lib/CodeGen/CodeGenAction.cpp b/clang/lib/CodeGen/CodeGenAction.cpp
index bb9aaba025fa59..51f54d178672d1 100644
--- a/clang/lib/CodeGen/CodeGenAction.cpp
+++ b/clang/lib/CodeGen/CodeGenAction.cpp
@@ -58,7 +58,7 @@ using namespace llvm;
 #define DEBUG_TYPE "codegenaction"
 
 namespace llvm {
-extern cl::opt<bool> ClRelinkBuiltinBitcodePostop;
+extern cl::opt<bool> ClLinkBuiltinBitcodePostopt;
 }
 
 namespace clang {
@@ -359,7 +359,7 @@ void BackendConsumer::HandleTranslationUnit(ASTContext &C) {
   }
 
   // Link each LinkModule into our module.
-  if (LinkInModules(getModule()))
+  if (!LinkBuiltinBitcodesPostopt && LinkInModules(getModule()))
     return;
 
   for (auto &F : getModule()->functions()) {
@@ -1213,7 +1213,7 @@ void CodeGenAction::ExecuteAction() {
                          std::move(LinkModules), *VMContext, nullptr);
 
   // Link in each pending link module.
-  if (Result.LinkInModules(&*TheModule))
+  if (!LinkBuiltinBitcodesPostopt && Result.LinkInModules(&*TheModule))
     return;
 
   // PR44896: Force DiscardValueNames as false. DiscardValueNames cannot be
diff --git a/clang/lib/CodeGen/LinkInModulesPass.cpp b/clang/lib/CodeGen/LinkInModulesPass.cpp
index 929539cc8f3346..ce1c0ebe046a61 100644
--- a/clang/lib/CodeGen/LinkInModulesPass.cpp
+++ b/clang/lib/CodeGen/LinkInModulesPass.cpp
@@ -28,10 +28,6 @@ PreservedAnalyses LinkInModulesPass::run(Module &M, ModuleAnalysisManager &AM) {
   if (!BC)
     return PreservedAnalyses::all();
 
-  // Re-load bitcode modules from files
-  if (BC->ReloadModules(&M))
-    report_fatal_error("Bitcode module re-loading failed, aborted!");
-
   if (BC->LinkInModules(&M, ShouldLinkFiles))
     report_fatal_error("Bitcode module re-linking failed, aborted!");
 

``````````

</details>


https://github.com/llvm/llvm-project/pull/85672