[BasicAA][TLI] Treat local-linkage globals or known environments as not aliasing errno

llvm/include/llvm/Analysis/TargetLibraryInfo.h

@@ -89,6 +89,7 @@ class TargetLibraryInfoImpl {
 #include "llvm/Analysis/TargetLibraryInfo.inc"
   bool ShouldExtI32Param, ShouldExtI32Return, ShouldSignExtI32Param, ShouldSignExtI32Return;
   unsigned SizeOfInt;
+  bool IsErrnoFunctionCall;
 
   enum AvailabilityState {
     StandardName = 3, // (memset to all ones)
@@ -256,6 +257,8 @@ class TargetLibraryInfoImpl {
   /// conventions.
   LLVM_ABI static bool isCallingConvCCompatible(CallBase *CI);
   LLVM_ABI static bool isCallingConvCCompatible(Function *Callee);
+
+  bool isErrnoFunctionCall() const { return IsErrnoFunctionCall; }
 };
 
 /// Provides information about what library functions are available for
@@ -601,6 +604,10 @@ class TargetLibraryInfo {
   bool isKnownVectorFunctionInLibrary(StringRef F) const {
     return this->isFunctionVectorizable(F);
   }
+
+  /// Returns whether `errno` is defined as a function call on known
+  /// environments.
+  bool isErrnoFunctionCall() const { return Impl->isErrnoFunctionCall(); }
 };
 
 /// Analysis pass providing the \c TargetLibraryInfo.

llvm/lib/Analysis/BasicAliasAnalysis.cpp

@@ -1001,7 +1001,10 @@ ModRefInfo BasicAAResult::getModRefInfo(const CallBase *Call,
 
   // Refine accesses to errno memory.
   if ((ErrnoMR | Result) != Result) {
-    if (AAQI.AAR.aliasErrno(Loc, Call->getModule()) != AliasResult::NoAlias) {
+    // Do not make any assumptions about errno on freestanding environments.
+    bool IsFreestanding = Call->getFunction()->hasFnAttribute("no-builtins");
+    if (IsFreestanding ||
+        AAQI.AAR.aliasErrno(Loc, Call->getModule()) != AliasResult::NoAlias) {
       // Exclusion conditions do not hold, this memory location may alias errno.
       Result |= ErrnoMR;
     }
@@ -1870,8 +1873,21 @@ AliasResult BasicAAResult::aliasErrno(const MemoryLocation &Loc,
       Loc.Size.getValue().getKnownMinValue() * 8 > TLI.getIntSize())
     return AliasResult::NoAlias;
 
-  if (isIdentifiedFunctionLocal(getUnderlyingObject(Loc.Ptr)))
+  const Value *Object = getUnderlyingObject(Loc.Ptr);
+  if (isIdentifiedFunctionLocal(Object))
     return AliasResult::NoAlias;
+
+  if (auto *GV = dyn_cast<GlobalVariable>(Object)) {
+    // Errno cannot alias internal/private globals.
+    if (GV->hasLocalLinkage())
+      return AliasResult::NoAlias;
+
+    // Neither can errno alias globals where environments define it as a
+    // function call.
+    if (TLI.isErrnoFunctionCall())
+      return AliasResult::NoAlias;
+  }
+
   return AliasResult::MayAlias;
 }
 

llvm/lib/Analysis/TargetLibraryInfo.cpp

@@ -905,8 +905,19 @@ static void initialize(TargetLibraryInfoImpl &TLI, const Triple &T,
   initializeLibCalls(TLI, T, StandardNames, VecLib);
 }
 
+static bool initializeIsErrnoFunctionCall(const Triple &T) {
+  // Assume errno is implemented as a function call on the following
+  // known environments.
+  // TODO: Could refine them.
+  return T.isOSDarwin() || T.isAndroid() || T.isGNUEnvironment() ||
+         T.isMusl() || T.getEnvironment() == Triple::LLVM ||
+         T.getEnvironment() == Triple::Mlibc ||
+         T.getEnvironment() == Triple::MSVC;
+}
+
 TargetLibraryInfoImpl::TargetLibraryInfoImpl(const Triple &T,
-                                             VectorLibrary VecLib) {
+                                             VectorLibrary VecLib)
+    : IsErrnoFunctionCall(initializeIsErrnoFunctionCall(T)) {
   // Default to everything being available.
   memset(AvailableArray, -1, sizeof(AvailableArray));
 
@@ -918,7 +929,7 @@ TargetLibraryInfoImpl::TargetLibraryInfoImpl(const TargetLibraryInfoImpl &TLI)
       ShouldExtI32Return(TLI.ShouldExtI32Return),
       ShouldSignExtI32Param(TLI.ShouldSignExtI32Param),
       ShouldSignExtI32Return(TLI.ShouldSignExtI32Return),
-      SizeOfInt(TLI.SizeOfInt) {
+      SizeOfInt(TLI.SizeOfInt), IsErrnoFunctionCall(TLI.IsErrnoFunctionCall) {
   memcpy(AvailableArray, TLI.AvailableArray, sizeof(AvailableArray));
   VectorDescs = TLI.VectorDescs;
   ScalarDescs = TLI.ScalarDescs;
@@ -930,7 +941,7 @@ TargetLibraryInfoImpl::TargetLibraryInfoImpl(TargetLibraryInfoImpl &&TLI)
       ShouldExtI32Return(TLI.ShouldExtI32Return),
       ShouldSignExtI32Param(TLI.ShouldSignExtI32Param),
       ShouldSignExtI32Return(TLI.ShouldSignExtI32Return),
-      SizeOfInt(TLI.SizeOfInt) {
+      SizeOfInt(TLI.SizeOfInt), IsErrnoFunctionCall(TLI.IsErrnoFunctionCall) {
   std::move(std::begin(TLI.AvailableArray), std::end(TLI.AvailableArray),
             AvailableArray);
   VectorDescs = TLI.VectorDescs;
@@ -944,6 +955,7 @@ TargetLibraryInfoImpl &TargetLibraryInfoImpl::operator=(const TargetLibraryInfoI
   ShouldSignExtI32Param = TLI.ShouldSignExtI32Param;
   ShouldSignExtI32Return = TLI.ShouldSignExtI32Return;
   SizeOfInt = TLI.SizeOfInt;
+  IsErrnoFunctionCall = TLI.IsErrnoFunctionCall;
   memcpy(AvailableArray, TLI.AvailableArray, sizeof(AvailableArray));
   return *this;
 }
@@ -955,6 +967,7 @@ TargetLibraryInfoImpl &TargetLibraryInfoImpl::operator=(TargetLibraryInfoImpl &&
   ShouldSignExtI32Param = TLI.ShouldSignExtI32Param;
   ShouldSignExtI32Return = TLI.ShouldSignExtI32Return;
   SizeOfInt = TLI.SizeOfInt;
+  IsErrnoFunctionCall = TLI.IsErrnoFunctionCall;
   std::move(std::begin(TLI.AvailableArray), std::end(TLI.AvailableArray),
             AvailableArray);
   return *this;

llvm/test/Transforms/InstCombine/may-alias-errno.ll

@@ -1,5 +1,5 @@
 ; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --version 5
-; RUN: opt -S -passes=instcombine < %s | FileCheck %s
+; RUN: opt -S -passes=instcombine -mtriple=aarch64-linux-gnu < %s | FileCheck %s
 
 ; sinf clobbering errno, but %p cannot alias errno per C/C++ strict aliasing rules via TBAA.
 ; Can do constant store-to-load forwarding.
@@ -149,6 +149,61 @@ entry:
   ret <vscale x 4 x i32> %v
 }
 
+@internal_g = internal global i32 0
+
+; errno cannot alias an internal global variable, can do constant store-to-load forwarding.
+define i32 @does_not_alias_errno_internal_global(float %f) {
+; CHECK-LABEL: define i32 @does_not_alias_errno_internal_global(
+; CHECK-SAME: float [[F:%.*]]) {
+; CHECK-NEXT:  [[ENTRY:.*:]]
+; CHECK-NEXT:    store i32 42, ptr @internal_g, align 4
+; CHECK-NEXT:    [[CALL:%.*]] = call float @sinf(float [[F]])
+; CHECK-NEXT:    ret i32 42
+;
+entry:
+  store i32 42, ptr @internal_g, align 4
+  %call = call float @sinf(float %f)
+  %v = load i32, ptr @internal_g, align 4
+  ret i32 %v
+}
+
+@external_g = external global i32
+
+; errno cannot alias an external global variable in GNU environment,
+; can do constant store-to-load forwarding.
+define i32 @does_not_alias_errno_external_known_environment(float %f) {
+; CHECK-LABEL: define i32 @does_not_alias_errno_external_known_environment(
+; CHECK-SAME: float [[F:%.*]]) {
+; CHECK-NEXT:  [[ENTRY:.*:]]
+; CHECK-NEXT:    store i32 42, ptr @external_g, align 4
+; CHECK-NEXT:    [[CALL:%.*]] = call float @sinf(float [[F]])
+; CHECK-NEXT:    ret i32 42
+;
+entry:
+  store i32 42, ptr @external_g, align 4
+  %call = call float @sinf(float %f)
+  %v = load i32, ptr @external_g, align 4
+  ret i32 %v
+}
+
+; Do not make any assumptions when may be targeting freestanding
+; environments (which implies nobuiltin).
+define i32 @may_alias_errno_nobuiltin(float %f) "no-builtins" {
+; CHECK-LABEL: define i32 @may_alias_errno_nobuiltin(
+; CHECK-SAME: float [[F:%.*]]) #[[ATTR0:[0-9]+]] {
+; CHECK-NEXT:  [[ENTRY:.*:]]
+; CHECK-NEXT:    store i32 42, ptr @internal_g, align 4
+; CHECK-NEXT:    [[CALL:%.*]] = call float @sinf(float [[F]])
+; CHECK-NEXT:    [[V:%.*]] = load i32, ptr @internal_g, align 4
+; CHECK-NEXT:    ret i32 [[V]]
+;
+entry:
+  store i32 42, ptr @internal_g, align 4
+  %call = call float @sinf(float %f)
+  %v = load i32, ptr @internal_g, align 4
+  ret i32 %v
+}
+
 declare float @sinf(float) memory(errnomem: write)
 declare float @read_errno(ptr) memory(argmem: write, errnomem: read)
 declare void @escape(ptr %p)

llvm/unittests/Analysis/TargetLibraryInfoTest.cpp

@@ -703,6 +703,25 @@ TEST_F(TargetLibraryInfoTest, ValidProto) {
   }
 }
 
+TEST_F(TargetLibraryInfoTest, IsErrnoGlobal) {
+  using TLII = TargetLibraryInfoImpl;
+
+  // Errno is defined as a function call on the following environments.
+  EXPECT_TRUE(TLII(Triple("arm64-apple-macosx")).isErrnoFunctionCall());
+  EXPECT_TRUE(TLII(Triple("arm--linux-androideabi")).isErrnoFunctionCall());
+  EXPECT_TRUE(
+      TLII(Triple("armv7-unknown-freebsd-gnueabihf")).isErrnoFunctionCall());
+  EXPECT_TRUE(TLII(Triple("riscv32-unknown-linux-musl")).isErrnoFunctionCall());
+  EXPECT_TRUE(TLII(Triple("x86_64-pc-windows-msvc")).isErrnoFunctionCall());
+  EXPECT_TRUE(TLII(Triple("x86_64-unknown-linux-gnu")).isErrnoFunctionCall());
+
+  // Unknown.
+  EXPECT_FALSE(TLII(Triple("aarch64-unknown-unknown")).isErrnoFunctionCall());
+  EXPECT_FALSE(TLII(Triple("arm-none-eabi")).isErrnoFunctionCall());
+  EXPECT_FALSE(TLII(Triple("powerpc-none-none")).isErrnoFunctionCall());
+  EXPECT_FALSE(TLII(Triple("x86_64-pc-linux")).isErrnoFunctionCall());
+}
+
 namespace {
 
 /// Creates TLI for AArch64 and uses it to get the LibFunc names for the given