Add SimplifyTypeTests pass.

This pass figures out whether inlining has exposed a constant address to
a lowered type test, and remove the test if so and the address is known
to pass the test. Unfortunately this pass ends up needing to reverse
engineer what LowerTypeTests did; this is currently inherent to the design
of ThinLTO importing where LowerTypeTests needs to run at the start.

Reviewers: teresajohnson

Reviewed By: teresajohnson

Pull Request: #141327

Author: pcc

llvm/include/llvm/Transforms/IPO/LowerTypeTests.h

@@ -223,6 +223,11 @@ class LowerTypeTestsPass : public PassInfoMixin<LowerTypeTestsPass> {
   PreservedAnalyses run(Module &M, ModuleAnalysisManager &AM);
 };
 
+class SimplifyTypeTestsPass : public PassInfoMixin<SimplifyTypeTestsPass> {
+public:
+  PreservedAnalyses run(Module &M, ModuleAnalysisManager &AM);
+};
+
 } // end namespace llvm
 
 #endif // LLVM_TRANSFORMS_IPO_LOWERTYPETESTS_H

llvm/lib/Passes/PassBuilderPipelines.cpp

@@ -1287,6 +1287,9 @@ PassBuilder::buildModuleSimplificationPipeline(OptimizationLevel Level,
   // and argument promotion.
   MPM.addPass(DeadArgumentEliminationPass());
 
+  if (Phase == ThinOrFullLTOPhase::ThinLTOPostLink)
+    MPM.addPass(SimplifyTypeTestsPass());
+
   if (Phase != ThinOrFullLTOPhase::ThinLTOPreLink)
     MPM.addPass(CoroCleanupPass());
 

llvm/lib/Passes/PassRegistry.def

@@ -101,6 +101,7 @@ MODULE_PASS("jmc-instrumenter", JMCInstrumenterPass())
 MODULE_PASS("lower-emutls", LowerEmuTLSPass())
 MODULE_PASS("lower-global-dtors", LowerGlobalDtorsPass())
 MODULE_PASS("lower-ifunc", LowerIFuncPass())
+MODULE_PASS("simplify-type-tests", SimplifyTypeTestsPass())
 MODULE_PASS("lowertypetests", LowerTypeTestsPass())
 MODULE_PASS("fatlto-cleanup", FatLtoCleanup())
 MODULE_PASS("pgo-force-function-attrs", PGOForceFunctionAttrsPass(PGOOpt ? PGOOpt->ColdOptType : PGOOptions::ColdFuncOpt::Default))

llvm/lib/Transforms/IPO/LowerTypeTests.cpp

@@ -19,11 +19,14 @@
 #include "llvm/ADT/DenseMap.h"
 #include "llvm/ADT/EquivalenceClasses.h"
 #include "llvm/ADT/PointerUnion.h"
+#include "llvm/ADT/STLExtras.h"
 #include "llvm/ADT/SetVector.h"
 #include "llvm/ADT/SmallVector.h"
 #include "llvm/ADT/Statistic.h"
 #include "llvm/ADT/StringRef.h"
 #include "llvm/ADT/TinyPtrVector.h"
+#include "llvm/Analysis/LoopInfo.h"
+#include "llvm/Analysis/PostDominators.h"
 #include "llvm/Analysis/TargetTransformInfo.h"
 #include "llvm/Analysis/TypeMetadataUtils.h"
 #include "llvm/Analysis/ValueTracking.h"
@@ -2472,3 +2475,94 @@ PreservedAnalyses LowerTypeTestsPass::run(Module &M,
     return PreservedAnalyses::all();
   return PreservedAnalyses::none();
 }
+
+PreservedAnalyses SimplifyTypeTestsPass::run(Module &M,
+                                             ModuleAnalysisManager &AM) {
+  bool Changed = false;
+  // Figure out whether inlining has exposed a constant address to a lowered
+  // type test, and remove the test if so and the address is known to pass the
+  // test. Unfortunately this pass ends up needing to reverse engineer what
+  // LowerTypeTests did; this is currently inherent to the design of ThinLTO
+  // importing where LowerTypeTests needs to run at the start.
+  //
+  // We look for things like:
+  //
+  // sub (i64 ptrtoint (ptr @_Z2fpv to i64), i64 ptrtoint (ptr
+  // @__typeid__ZTSFvvE_global_addr to i64))
+  //
+  // which gets replaced with 0 if _Z2fpv (more specifically _Z2fpv.cfi, the
+  // function referred to by the jump table) is a member of the type _ZTSFvv, as
+  // well as things like
+  //
+  // icmp eq ptr @_Z2fpv, @__typeid__ZTSFvvE_global_addr
+  //
+  // which gets replaced with true if _Z2fpv is a member.
+  for (auto &GV : M.globals()) {
+    if (!GV.getName().starts_with("__typeid_") ||
+        !GV.getName().ends_with("_global_addr"))
+      continue;
+    // __typeid_foo_global_addr -> foo
+    auto *MD = MDString::get(M.getContext(),
+                             GV.getName().substr(9, GV.getName().size() - 21));
+    auto MaySimplifyPtr = [&](Value *Ptr) {
+      if (auto *GV = dyn_cast<GlobalValue>(Ptr))
+        if (auto *CFIGV = M.getNamedValue((GV->getName() + ".cfi").str()))
+          Ptr = CFIGV;
+      return isKnownTypeIdMember(MD, M.getDataLayout(), Ptr, 0);
+    };
+    auto MaySimplifyInt = [&](Value *Op) {
+      auto *PtrAsInt = dyn_cast<ConstantExpr>(Op);
+      if (!PtrAsInt || PtrAsInt->getOpcode() != Instruction::PtrToInt)
+        return false;
+      return MaySimplifyPtr(PtrAsInt->getOperand(0));
+    };
+    for (User *U : make_early_inc_range(GV.users())) {
+      if (auto *CI = dyn_cast<ICmpInst>(U)) {
+        if (CI->getPredicate() == CmpInst::ICMP_EQ &&
+            MaySimplifyPtr(CI->getOperand(0))) {
+          // This is an equality comparison (TypeTestResolution::Single case in
+          // lowerTypeTestCall). In this case we just replace the comparison
+          // with true.
+          CI->replaceAllUsesWith(ConstantInt::getTrue(M.getContext()));
+          CI->eraseFromParent();
+          Changed = true;
+        }
+      }
+      auto *CE = dyn_cast<ConstantExpr>(U);
+      if (!CE || CE->getOpcode() != Instruction::PtrToInt)
+        continue;
+      for (Use &U : make_early_inc_range(CE->uses())) {
+        auto *CE = dyn_cast<ConstantExpr>(U.getUser());
+        if (U.getOperandNo() == 1 && CE &&
+            CE->getOpcode() == Instruction::Sub &&
+            MaySimplifyInt(CE->getOperand(0))) {
+          // This is a computation of PtrOffset as generated by
+          // LowerTypeTestsModule::lowerTypeTestCall above. If
+          // isKnownTypeIdMember passes we just pretend it evaluated to 0. This
+          // should cause later passes to remove the range and alignment checks.
+          // The bitset checks won't be removed but those are uncommon.
+          CE->replaceAllUsesWith(ConstantInt::get(CE->getType(), 0));
+          Changed = true;
+        }
+        auto *CI = dyn_cast<ICmpInst>(U.getUser());
+        if (U.getOperandNo() == 1 && CI &&
+            CI->getPredicate() == CmpInst::ICMP_EQ &&
+            MaySimplifyInt(CI->getOperand(0))) {
+          // This is an equality comparison. Unlike in the case above it
+          // remained as an integer compare.
+          CI->replaceAllUsesWith(ConstantInt::getTrue(M.getContext()));
+          CI->eraseFromParent();
+          Changed = true;
+        }
+      }
+    }
+  }
+
+  if (!Changed)
+    return PreservedAnalyses::all();
+  PreservedAnalyses PA = PreservedAnalyses::none();
+  PA.preserve<DominatorTreeAnalysis>();
+  PA.preserve<PostDominatorTreeAnalysis>();
+  PA.preserve<LoopAnalysis>();
+  return PA;
+}

llvm/test/Other/new-pm-thinlto-postlink-defaults.ll

@@ -159,6 +159,7 @@
 ; CHECK-O-NEXT: Invalidating analysis: ShouldNotRunFunctionPassesAnalysis
 ; CHECK-O-NEXT: Invalidating analysis: InlineAdvisorAnalysis
 ; CHECK-O-NEXT: Running pass: DeadArgumentEliminationPass
+; CHECK-O-NEXT: Running pass: SimplifyTypeTestsPass
 ; CHECK-O-NEXT: Running pass: CoroCleanupPass
 ; CHECK-POSTLINK-O-NEXT: Running pass: GlobalOptPass
 ; CHECK-POSTLINK-O-NEXT: Running pass: GlobalDCEPass

llvm/test/Other/new-pm-thinlto-postlink-pgo-defaults.ll

@@ -143,6 +143,7 @@
 ; CHECK-O-NEXT: Invalidating analysis: ShouldNotRunFunctionPassesAnalysis
 ; CHECK-O-NEXT: Invalidating analysis: InlineAdvisorAnalysis
 ; CHECK-O-NEXT: Running pass: DeadArgumentEliminationPass
+; CHECK-O-NEXT: Running pass: SimplifyTypeTestsPass
 ; CHECK-O-NEXT: Running pass: CoroCleanupPass
 ; CHECK-O-NEXT: Running pass: GlobalOptPass
 ; CHECK-O-NEXT: Running pass: GlobalDCEPass

llvm/test/Other/new-pm-thinlto-postlink-samplepgo-defaults.ll

@@ -152,6 +152,7 @@
 ; CHECK-O-NEXT: Invalidating analysis: ShouldNotRunFunctionPassesAnalysis
 ; CHECK-O-NEXT: Invalidating analysis: InlineAdvisorAnalysis
 ; CHECK-O-NEXT: Running pass: DeadArgumentEliminationPass
+; CHECK-O-NEXT: Running pass: SimplifyTypeTestsPass
 ; CHECK-O-NEXT: Running pass: CoroCleanupPass
 ; CHECK-O-NEXT: Running pass: GlobalOptPass
 ; CHECK-O-NEXT: Running pass: GlobalDCEPass

llvm/test/Transforms/SimplifyTypeTests/basic.ll

@@ -0,0 +1,46 @@
+; Test that a lowered type test for a type is simplified to true
+; if the target is a constant member of that type.
+
+; RUN: opt -S %s -passes=simplify-type-tests | FileCheck %s
+
+; Test that the simplification does not occur if the type is wrong.
+ 
+; RUN: sed -e 's/"_ZTSFvvE"/"wrongtype"/g' %s | opt -S -passes=simplify-type-tests | FileCheck --check-prefix=WRONGTYPE %s
+
+target datalayout = "e-m:e-p270:32:32-p271:32:32-p272:64:64-i64:64-i128:128-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-unknown-linux-gnu"
+
+@__typeid__ZTSFvvE_global_addr = external hidden global [0 x i8], code_model "small"
+
+define void @_Z2fpv.cfi() !type !0 {
+  ret void
+}
+
+define i64 @main() {
+  %1 = icmp eq ptr @_Z2fpv, @__typeid__ZTSFvvE_global_addr
+  ; CHECK: br i1 true
+  ; WRONGTYPE: br i1 %
+  br i1 %1, label %3, label %2
+
+2:
+  tail call void @llvm.ubsantrap(i8 2)
+  unreachable
+
+3:
+  ; CHECK: br i1 true
+  ; WRONGTYPE: br i1 %
+  %c = icmp eq i64 ptrtoint (ptr @_Z2fpv to i64), ptrtoint (ptr @__typeid__ZTSFvvE_global_addr to i64)
+  br i1 %c, label %4, label %2
+
+4:
+  tail call void @_Z2fpv()
+  ; CHECK: ret i64 0
+  ; WRONGTYPE: ret i64 sub
+  ret i64 sub (i64 ptrtoint (ptr @_Z2fpv to i64), i64 ptrtoint (ptr @__typeid__ZTSFvvE_global_addr to i64))
+}
+
+declare void @llvm.ubsantrap(i8 immarg)
+
+declare hidden void @_Z2fpv()
+
+!0 = !{i64 0, !"_ZTSFvvE"}