[Analysis] Only use _unlocked stdio functions on linux

The existing comment said that the functions were available only
on GNU/Linux (and on certain Android versions), but only checked
T.isGNUEnvironment() which also is true on MinGW (for arch-windows-gnu
triplets), which doesn't have such functions.

Existing checks in the initialize function in TargetLibraryInfo.cpp
also use only T.isOSLinux() to check for glibc features.

This fixes use of stdio on MinGW.

Differential Revision: https://reviews.llvm.org/D47002

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@332581 91177308-0d34-0410-b5e6-96231b3b80d8

lib/Analysis/TargetLibraryInfo.cpp

@@ -482,7 +482,8 @@ static void initialize(TargetLibraryInfoImpl &TLI, const Triple &T,
     TLI.setUnavailable(LibFunc_sinhl_finite);
   }
 
-  if (T.isGNUEnvironment() || (T.isAndroid() && !T.isAndroidVersionLT(28))) {
+  if ((T.isOSLinux() && T.isGNUEnvironment()) ||
+      (T.isAndroid() && !T.isAndroidVersionLT(28))) {
     // available IO unlocked variants on GNU/Linux and Android P or later
     TLI.setAvailable(LibFunc_getc_unlocked);
     TLI.setAvailable(LibFunc_getchar_unlocked);

test/Transforms/InstCombine/unlocked-stdio-mingw.ll

@@ -0,0 +1,23 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
+; RUN: opt < %s -instcombine -S -mtriple=x86_64-w64-mingw32 | FileCheck %s
+
+%struct._iobuf = type { i8*, i32, i8*, i32, i32, i32, i32, i8* }
+
+@.str = private unnamed_addr constant [5 x i8] c"file\00", align 1
+@.str.1 = private unnamed_addr constant [2 x i8] c"w\00", align 1
+
+; Check that this still uses the plain fputc instead of fputc_unlocked
+; for MinGW targets.
+define void @external_fputc_test() {
+; CHECK-LABEL: @external_fputc_test(
+; CHECK-NEXT:    [[CALL:%.*]] = call %struct._iobuf* @fopen(i8* getelementptr inbounds ([5 x i8], [5 x i8]* @.str, i64 0, i64 0), i8* getelementptr inbounds ([2 x i8], [2 x i8]* @.str.1, i64 0, i64 0))
+; CHECK-NEXT:    [[CALL1:%.*]] = call i32 @fputc(i32 99, %struct._iobuf* [[CALL]])
+; CHECK-NEXT:    ret void
+;
+  %call = call %struct._iobuf* @fopen(i8* getelementptr inbounds ([5 x i8], [5 x i8]* @.str, i64 0, i64 0), i8* getelementptr inbounds ([2 x i8], [2 x i8]* @.str.1, i64 0, i64 0))
+  %call1 = call i32 @fputc(i32 99, %struct._iobuf* %call)
+  ret void
+}
+
+declare %struct._iobuf* @fopen(i8*, i8*)
+declare i32 @fputc(i32, %struct._iobuf* nocapture)