[llvm] [CodeGen] Derive the regalloc pipeline from the allocator, remove -optimize-regalloc (PR #215740)

[Fangrui Song via llvm-commits]

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@@ -1392,6 +1376,18 @@ static void initializeDefaultRegisterAllocatorOnce() {
     RegisterRegAlloc::setDefault(RegAlloc);
 }
 
+bool TargetPassConfig::getOptimizeRegAlloc() const {
+  // An explicit -regalloc choice implies its pipeline: only the fast
+  // allocator uses the unoptimized one.
+  llvm::call_once(InitializeDefaultRegisterAllocatorFlag,
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MaskRay wrote:

Thanks!

Done. `getOptimizeRegAlloc` is called before the pipeline branches into `addFastRegAlloc`/`addOptimizedRegAlloc`, so the default is already initialized

https://github.com/llvm/llvm-project/pull/215740