[CodeGen][LTO] Rename some misleading variables (#65185)

Some flags named "IsLTO" and "IsThinLTO" implied they described
compilation modes, but with Unified LTO this is no longer true. Rename
these to "PrepForXXX" to be less confusing to readers. Also, deleted
"IsThinOrUnifiedLTO" because Unified implies PrepareForThinLTO.

Author: pogo59

clang/lib/CodeGen/BackendUtil.cpp

@@ -927,8 +927,8 @@ void EmitAssemblyHelper::RunOptimizationPipeline(
     // configure the pipeline.
     OptimizationLevel Level = mapToLevel(CodeGenOpts);
 
-    bool IsThinLTO = CodeGenOpts.PrepareForThinLTO;
-    bool IsLTO = CodeGenOpts.PrepareForLTO;
+    const bool PrepareForThinLTO = CodeGenOpts.PrepareForThinLTO;
+    const bool PrepareForLTO = CodeGenOpts.PrepareForLTO;
 
     if (LangOpts.ObjCAutoRefCount) {
       PB.registerPipelineStartEPCallback(
@@ -1017,14 +1017,13 @@ void EmitAssemblyHelper::RunOptimizationPipeline(
           });
     }
 
-    bool IsThinOrUnifiedLTO = IsThinLTO || (IsLTO && CodeGenOpts.UnifiedLTO);
     if (CodeGenOpts.FatLTO) {
-      MPM = PB.buildFatLTODefaultPipeline(Level, IsThinOrUnifiedLTO,
-                                          IsThinOrUnifiedLTO ||
+      MPM = PB.buildFatLTODefaultPipeline(Level, PrepareForThinLTO,
+                                          PrepareForThinLTO ||
                                               shouldEmitRegularLTOSummary());
-    } else if (IsThinOrUnifiedLTO) {
+    } else if (PrepareForThinLTO) {
       MPM = PB.buildThinLTOPreLinkDefaultPipeline(Level);
-    } else if (IsLTO) {
+    } else if (PrepareForLTO) {
       MPM = PB.buildLTOPreLinkDefaultPipeline(Level);
     } else {
       MPM = PB.buildPerModuleDefaultPipeline(Level);
@@ -1081,12 +1080,9 @@ void EmitAssemblyHelper::RunOptimizationPipeline(
   if (CodeGenOpts.FatLTO) {
     // Set module flags, like EnableSplitLTOUnit and UnifiedLTO, since FatLTO
     // uses a different action than Backend_EmitBC or Backend_EmitLL.
-    bool IsThinOrUnifiedLTO =
-        CodeGenOpts.PrepareForThinLTO ||
-        (CodeGenOpts.PrepareForLTO && CodeGenOpts.UnifiedLTO);
     if (!TheModule->getModuleFlag("ThinLTO"))
       TheModule->addModuleFlag(Module::Error, "ThinLTO",
-                               uint32_t(IsThinOrUnifiedLTO));
+                               uint32_t(CodeGenOpts.PrepareForThinLTO));
     if (!TheModule->getModuleFlag("EnableSplitLTOUnit"))
       TheModule->addModuleFlag(Module::Error, "EnableSplitLTOUnit",
                                uint32_t(CodeGenOpts.EnableSplitLTOUnit));