[llvm] e976385 - [llvm][GlobalOpt] Optimize statically resolvable IFuncs (#80606)
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Tue Feb 6 13:59:01 PST 2024
Author: Jon Roelofs
Date: 2024-02-06T13:58:58-08:00
New Revision: e976385415da45650952316db63c4ccd370e4030
URL: https://github.com/llvm/llvm-project/commit/e976385415da45650952316db63c4ccd370e4030
DIFF: https://github.com/llvm/llvm-project/commit/e976385415da45650952316db63c4ccd370e4030.diff
LOG: [llvm][GlobalOpt] Optimize statically resolvable IFuncs (#80606)
Added:
llvm/test/Transforms/GlobalOpt/resolve-static-ifunc.ll
Modified:
llvm/lib/Transforms/IPO/GlobalOpt.cpp
Removed:
################################################################################
diff --git a/llvm/lib/Transforms/IPO/GlobalOpt.cpp b/llvm/lib/Transforms/IPO/GlobalOpt.cpp
index 951372adcfa93..42828b4f41680 100644
--- a/llvm/lib/Transforms/IPO/GlobalOpt.cpp
+++ b/llvm/lib/Transforms/IPO/GlobalOpt.cpp
@@ -89,6 +89,8 @@ STATISTIC(NumAliasesRemoved, "Number of global aliases eliminated");
STATISTIC(NumCXXDtorsRemoved, "Number of global C++ destructors removed");
STATISTIC(NumInternalFunc, "Number of internal functions");
STATISTIC(NumColdCC, "Number of functions marked coldcc");
+STATISTIC(NumIFuncsResolved, "Number of statically resolved IFuncs");
+STATISTIC(NumIFuncsDeleted, "Number of IFuncs removed");
static cl::opt<bool>
EnableColdCCStressTest("enable-coldcc-stress-test",
@@ -2404,6 +2406,60 @@ static bool OptimizeEmptyGlobalCXXDtors(Function *CXAAtExitFn) {
return Changed;
}
+static Function *hasSideeffectFreeStaticResolution(GlobalIFunc &IF) {
+ if (IF.isInterposable())
+ return nullptr;
+
+ Function *Resolver = IF.getResolverFunction();
+ if (!Resolver)
+ return nullptr;
+
+ if (Resolver->isInterposable())
+ return nullptr;
+
+ // Only handle functions that have been optimized into a single basic block.
+ auto It = Resolver->begin();
+ if (++It != Resolver->end())
+ return nullptr;
+
+ BasicBlock &BB = Resolver->getEntryBlock();
+
+ if (any_of(BB, [](Instruction &I) { return I.mayHaveSideEffects(); }))
+ return nullptr;
+
+ auto *Ret = dyn_cast<ReturnInst>(BB.getTerminator());
+ if (!Ret)
+ return nullptr;
+
+ return dyn_cast<Function>(Ret->getReturnValue());
+}
+
+/// Find IFuncs that have resolvers that always point at the same statically
+/// known callee, and replace their callers with a direct call.
+static bool OptimizeStaticIFuncs(Module &M) {
+ bool Changed = false;
+ for (GlobalIFunc &IF : M.ifuncs())
+ if (Function *Callee = hasSideeffectFreeStaticResolution(IF))
+ if (!IF.use_empty()) {
+ IF.replaceAllUsesWith(Callee);
+ NumIFuncsResolved++;
+ Changed = true;
+ }
+ return Changed;
+}
+
+static bool
+DeleteDeadIFuncs(Module &M,
+ SmallPtrSetImpl<const Comdat *> &NotDiscardableComdats) {
+ bool Changed = false;
+ for (GlobalIFunc &IF : make_early_inc_range(M.ifuncs()))
+ if (deleteIfDead(IF, NotDiscardableComdats)) {
+ NumIFuncsDeleted++;
+ Changed = true;
+ }
+ return Changed;
+}
+
static bool
optimizeGlobalsInModule(Module &M, const DataLayout &DL,
function_ref<TargetLibraryInfo &(Function &)> GetTLI,
@@ -2464,6 +2520,12 @@ optimizeGlobalsInModule(Module &M, const DataLayout &DL,
if (CXAAtExitFn)
LocalChange |= OptimizeEmptyGlobalCXXDtors(CXAAtExitFn);
+ // Optimize IFuncs whose callee's are statically known.
+ LocalChange |= OptimizeStaticIFuncs(M);
+
+ // Remove any IFuncs that are now dead.
+ LocalChange |= DeleteDeadIFuncs(M, NotDiscardableComdats);
+
Changed |= LocalChange;
}
diff --git a/llvm/test/Transforms/GlobalOpt/resolve-static-ifunc.ll b/llvm/test/Transforms/GlobalOpt/resolve-static-ifunc.ll
new file mode 100644
index 0000000000000..2a1717304fb4c
--- /dev/null
+++ b/llvm/test/Transforms/GlobalOpt/resolve-static-ifunc.ll
@@ -0,0 +1,109 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --function caller --check-globals all --version 4
+; RUN: opt --passes=globalopt -o - -S < %s | FileCheck %s --implicit-check-not=trivial\.ifunc --implicit-check-not=dead_ifunc
+
+target datalayout = "e-m:e-i8:8:32-i16:16:32-i64:64-i128:128-n32:64-S128"
+target triple = "aarch64-unknown-linux-gnu"
+
+ at trivial.ifunc = internal ifunc void (), ptr @trivial.resolver
+;.
+; CHECK: @unknown_condition = external local_unnamed_addr global i1
+; CHECK: @external_ifunc.ifunc = dso_local ifunc void (), ptr @external_ifunc.resolver
+; CHECK: @complex.ifunc = internal ifunc void (), ptr @complex.resolver
+; CHECK: @sideeffects.ifunc = internal ifunc void (), ptr @sideeffects.resolver
+; CHECK: @interposable_ifunc.ifunc = internal ifunc void (), ptr @interposable_ifunc.resolver
+; CHECK: @interposable_resolver.ifunc = weak ifunc void (), ptr @interposable_resolver.resolver
+;.
+define ptr @trivial.resolver() {
+ ret ptr @trivial._Msimd
+}
+define void @trivial._Msimd() {
+ ret void
+}
+define void @trivial.default() {
+ ret void
+}
+
+
+ at dead_ifunc.ifunc = internal ifunc void (), ptr @trivial.resolver
+
+ at external_ifunc.ifunc = dso_local ifunc void (), ptr @external_ifunc.resolver
+define ptr @external_ifunc.resolver() {
+ ret ptr @external_ifunc._Msimd
+}
+define void @external_ifunc._Msimd() {
+ ret void
+}
+define void @external_ifunc.default() {
+ ret void
+}
+
+ at unknown_condition = external global i1
+ at complex.ifunc = internal ifunc void (), ptr @complex.resolver
+define ptr @complex.resolver() {
+entry:
+ %v = load i1, ptr @unknown_condition
+ br i1 %v, label %fast, label %slow
+fast:
+ ret ptr @complex._Msimd
+slow:
+ ret ptr @complex._Msimd
+}
+define void @complex._Msimd() {
+ ret void
+}
+define void @complex.default() {
+ ret void
+}
+
+ at sideeffects.ifunc = internal ifunc void (), ptr @sideeffects.resolver
+define ptr @sideeffects.resolver() {
+ store i1 0, ptr @unknown_condition
+ ret ptr @sideeffects.default
+}
+define void @sideeffects._Msimd() {
+ ret void
+}
+define void @sideeffects.default() {
+ ret void
+}
+
+ at interposable_ifunc.ifunc = internal ifunc void (), ptr @interposable_ifunc.resolver
+define weak ptr @interposable_ifunc.resolver() {
+ ret ptr @interposable_ifunc.resolver
+}
+define void @interposable_ifunc._Msimd() {
+ ret void
+}
+define void @interposable_ifunc.default() {
+ ret void
+}
+
+ at interposable_resolver.ifunc = weak ifunc void (), ptr @interposable_resolver.resolver
+define ptr @interposable_resolver.resolver() {
+ ret ptr @interposable_resolver.resolver
+}
+define void @interposable_resolver._Msimd() {
+ ret void
+}
+define void @interposable_resolver.default() {
+ ret void
+}
+
+define void @caller() {
+; CHECK-LABEL: define void @caller() local_unnamed_addr {
+; CHECK-NEXT: call void @trivial._Msimd()
+; CHECK-NEXT: call void @external_ifunc._Msimd()
+; CHECK-NEXT: call void @complex.ifunc()
+; CHECK-NEXT: call void @sideeffects.ifunc()
+; CHECK-NEXT: call void @interposable_ifunc.ifunc()
+; CHECK-NEXT: call void @interposable_resolver.ifunc()
+; CHECK-NEXT: ret void
+;
+ call void @trivial.ifunc()
+ call void @external_ifunc.ifunc()
+ call void @complex.ifunc()
+ call void @sideeffects.ifunc()
+ call void @interposable_ifunc.ifunc()
+ call void @interposable_resolver.ifunc()
+ ret void
+}
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