X86: use the correct alloca symbol for Windows Itanium

Windows itanium targets the MSVCRT, and the stack probe symbol is provided by
MSVCRT.  This corrects the emission of stack probes on i686-windows-itanium.

llvm-svn: 222439

llvm/lib/Target/X86/X86ISelLowering.cpp

@@ -20609,8 +20609,10 @@ X86TargetLowering::EmitLoweredWinAlloca(MachineInstr *MI,
         .addReg(X86::RAX);
     }
   } else {
-    const char *StackProbeSymbol =
+    const char *StackProbeSymbol = (Subtarget->isTargetKnownWindowsMSVC() ||
-      Subtarget->isTargetKnownWindowsMSVC() ? "_chkstk" : "_alloca";
+                                    Subtarget->isTargetWindowsItanium())
+                                       ? "_chkstk"
+                                       : "_alloca";
 
     BuildMI(*BB, MI, DL, TII->get(X86::CALLpcrel32))
       .addExternalSymbol(StackProbeSymbol)

llvm/lib/Target/X86/X86Subtarget.h

@@ -426,6 +426,10 @@ public:
     return TargetTriple.isWindowsGNUEnvironment();
   }
 
+  bool isTargetWindowsItanium() const {
+    return TargetTriple.isWindowsItaniumEnvironment();
+  }
+
   bool isTargetCygMing() const { return TargetTriple.isOSCygMing(); }
 
   bool isOSWindows() const { return TargetTriple.isOSWindows(); }

llvm/test/CodeGen/X86/windows-itanium-alloca.ll

@@ -0,0 +1,16 @@
+; RUN: llc -mtriple i686-windows-itanium -filetype asm -o - %s | FileCheck %s
+
+target datalayout = "e-m:w-p:32:32-i64:64-f80:32-n8:16:32-S32"
+target triple = "i686--windows-itanium"
+
+declare void @external(i8*)
+
+define dllexport void @alloca(i32 %sz) {
+entry:
+  %vla = alloca i8, i32 %sz, align 1
+  call void @external(i8* %vla)
+  ret void
+}
+
+; CHECK: __chkstk
+