[LTO] Run Argument Promotion before IPSCCP

Run ArgumentPromotion before IPSCCP in the LTO pipeline, to expose more
constants to be propagated. We also run PostOrderFunctionAttrs to
improve the information available to ArgumentPromotion's alias analysis,
and SROA to clean up allocas.

Author: hazzlim

llvm/lib/Passes/PassBuilderPipelines.cpp

@@ -1831,6 +1831,14 @@ PassBuilder::buildLTODefaultPipeline(OptimizationLevel Level,
     MPM.addPass(PGOIndirectCallPromotion(
         true /* InLTO */, PGOOpt && PGOOpt->Action == PGOOptions::SampleUse));
 
+    // Promoting by-reference arguments to by-value exposes more constants to
+    // IPSCCP.
+    MPM.addPass(createModuleToPostOrderCGSCCPassAdaptor(
+        PostOrderFunctionAttrsPass(/*SkipNonRecursive*/ true)));
+    MPM.addPass(
+        createModuleToPostOrderCGSCCPassAdaptor(ArgumentPromotionPass()));
+    MPM.addPass(createModuleToFunctionPassAdaptor(SROAPass(SROAOptions::ModifyCFG)));
+
     // Propagate constants at call sites into the functions they call.  This
     // opens opportunities for globalopt (and inlining) by substituting function
     // pointers passed as arguments to direct uses of functions.

llvm/test/Other/new-pm-lto-defaults.ll

@@ -41,14 +41,17 @@
 ; CHECK-O23SZ-NEXT: PGOIndirectCallPromotion
 ; CHECK-O23SZ-NEXT: Running analysis: ProfileSummaryAnalysis
 ; CHECK-O23SZ-NEXT: Running analysis: OptimizationRemarkEmitterAnalysis
-; CHECK-O23SZ-NEXT: Running pass: IPSCCPPass
-; CHECK-O23SZ-NEXT: Running analysis: AssumptionAnalysis on foo
-; CHECK-O23SZ-NEXT: Running pass: CalledValuePropagationPass
 ; CHECK-O-NEXT: Running analysis: InnerAnalysisManagerProxy<{{.*}}SCC
 ; CHECK-O-NEXT: Running analysis: LazyCallGraphAnalysis
 ; CHECK-O1-NEXT: Running analysis: TargetLibraryAnalysis
 ; CHECK-O-NEXT: Running analysis: FunctionAnalysisManagerCGSCCProxy
 ; CHECK-O-NEXT: Running analysis: OuterAnalysisManagerProxy<{{.*}}LazyCallGraph{{.*}}>
+; CHECK-O23SZ-NEXT: Running pass: PostOrderFunctionAttrsPass
+; CHECK-O23SZ-NEXT: Running pass: ArgumentPromotionPass
+; CHECK-O23SZ-NEXT: Running pass: SROAPass
+; CHECK-O23SZ-NEXT: Running analysis: AssumptionAnalysis on foo
+; CHECK-O23SZ-NEXT: Running pass: IPSCCPPass
+; CHECK-O23SZ-NEXT: Running pass: CalledValuePropagationPass
 ; CHECK-O-NEXT: Running pass: PostOrderFunctionAttrsPass
 ; CHECK-O-NEXT: Running analysis: AAManager
 ; CHECK-O-NEXT: Running analysis: BasicAA