[clang][CodeGen][AA] Add !llvm.errno.tbaa listing int-compatible TBAA nodes

Model integer accesses through an ad-hoc TBAA module-level metadata, so as to
disambiguate integer accesses from non-integer ones, at TBAA level. This is
purposefully as part of handling `errno` accesses, which are guaranteed to be
integer-compatible.

Author: antoniofrighetto

clang/lib/CodeGen/CodeGenModule.cpp

@@ -83,6 +83,7 @@ static llvm::cl::opt<bool> LimitedCoverage(
     llvm::cl::desc("Emit limited coverage mapping information (experimental)"));
 
 static const char AnnotationSection[] = "llvm.metadata";
+static constexpr auto ErrnoTBAAMDName = "llvm.errno.tbaa";
 
 static CGCXXABI *createCXXABI(CodeGenModule &CGM) {
   switch (CGM.getContext().getCXXABIKind()) {
@@ -1457,6 +1458,12 @@ void CodeGenModule::Release() {
       }
     }
   }
+
+  if (TBAA) {
+    auto *ErrnoTBAAMD = TheModule.getOrInsertNamedMetadata(ErrnoTBAAMDName);
+    llvm::MDNode *IntegerNode = TBAA->getTypeInfo(Context.IntTy);
+    ErrnoTBAAMD->addOperand(IntegerNode);
+  }
 }
 
 void CodeGenModule::EmitOpenCLMetadata() {

llvm/test/Transforms/GVN/does-clobber-errno.ll

@@ -1,15 +1,15 @@
 ; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --version 5
 ; RUN: opt -passes=gvn -S < %s | FileCheck %s
 
-; FIXME: This is a miscompilation.
 define noundef i32 @test_malloc_clobbering_errno() {
 ; CHECK-LABEL: define noundef i32 @test_malloc_clobbering_errno() {
 ; CHECK-NEXT:    [[TMP1:%.*]] = alloca ptr, align 8
 ; CHECK-NEXT:    [[TMP2:%.*]] = call ptr @__errno_location()
 ; CHECK-NEXT:    store i32 0, ptr [[TMP2]], align 4
 ; CHECK-NEXT:    [[TMP3:%.*]] = call noalias ptr @malloc(i64 1844674407370955161)
 ; CHECK-NEXT:    store volatile ptr [[TMP3]], ptr [[TMP1]], align 8
-; CHECK-NEXT:    ret i32 0
+; CHECK-NEXT:    [[TMP4:%.*]] = load i32, ptr [[TMP2]], align 4
+; CHECK-NEXT:    ret i32 [[TMP4]]
 ;
   %1 = alloca ptr, align 8
   %2 = call ptr @__errno_location()
@@ -24,4 +24,4 @@ declare ptr @__errno_location() #1
 declare noalias ptr @malloc(i64) #2
 
 attributes #1 = { mustprogress nofree nosync nounwind willreturn memory(none) }
-attributes #2 = { mustprogress nofree nounwind willreturn memory(inaccessiblemem: readwrite) }
+attributes #2 = { mustprogress nofree nounwind willreturn memory(inaccessiblemem: readwrite, errnomem: readwrite) }

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

@@ -0,0 +1,49 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --version 5
+; RUN: opt -S -passes=instcombine < %s | FileCheck %s
+
+; sinf clobbering errno, but %p cannot alias errno per C/C++ strict aliasing rules via TBAA.
+; Hence, can do constant store-to-load forwarding.
+define float @does_not_alias_errno(ptr noundef %p, float noundef %f) {
+; CHECK-LABEL: define float @does_not_alias_errno(
+; CHECK-SAME: ptr noundef [[P:%.*]], float noundef [[F:%.*]]) {
+; CHECK-NEXT:  [[ENTRY:.*:]]
+; CHECK-NEXT:    store float 0.000000e+00, ptr [[P]], align 4, !tbaa [[TBAA3:![0-9]+]]
+; CHECK-NEXT:    [[CALL:%.*]] = call float @sinf(float noundef [[F]]), !tbaa [[TBAA5:![0-9]+]]
+; CHECK-NEXT:    ret float 0.000000e+00
+;
+entry:
+  store float 0.000000e+00, ptr %p, align 4, !tbaa !3
+  %call = call float @sinf(float noundef %f), !tbaa !10
+  %0 = load float, ptr %p, align 4, !tbaa !3
+  ret float %0
+}
+
+; sinf clobbering errno, unknown TBAA info, %p may alias errno
+define float @may_alias_errno(ptr noundef %p, float noundef %f) {
+; CHECK-LABEL: define float @may_alias_errno(
+; CHECK-SAME: ptr noundef [[P:%.*]], float noundef [[F:%.*]]) {
+; CHECK-NEXT:  [[ENTRY:.*:]]
+; CHECK-NEXT:    store float 0.000000e+00, ptr [[P]], align 4
+; CHECK-NEXT:    [[CALL:%.*]] = call float @sinf(float noundef [[F]])
+; CHECK-NEXT:    [[TMP0:%.*]] = load float, ptr [[P]], align 4
+; CHECK-NEXT:    ret float [[TMP0]]
+;
+entry:
+  store float 0.000000e+00, ptr %p, align 4
+  %call = call float @sinf(float noundef %f)
+  %0 = load float, ptr %p, align 4
+  ret float %0
+}
+
+declare float @sinf(float noundef) #1
+
+attributes #1 = { mustprogress nofree nounwind willreturn memory(errnomem: write) }
+
+!llvm.errno.tbaa = !{!0}
+
+!0 = !{!"int", !1, i64 0}
+!1 = !{!"omnipotent char", !2, i64 0}
+!2 = !{!"Simple C/C++ TBAA"}
+!3 = !{!4, !4, i64 0}
+!4 = !{!"float", !1, i64 0}
+!10 = !{!0, !0, i64 0}