[X86] Fix SP adjustment in stack probes emitted on 32-bit Windows.

Commit r306010 adjusted the condition as follows:

-  if (Is64Bit) {
+  if (!STI.isTargetWin32()) {

The intent was to preserve the behavior on all Windows platforms
but extend the behavior on 64-bit Windows platforms to every
other one. (Before r306010, emitStackProbeCall only ever executed
when emitting code for Windows triples.)

Unfortunately,
  if (Is64Bit && STI.isOSWindows())
is not the same as
  if (!STI.isTargetWin32())
because of the way isTargetWin32() is defined:

  bool isTargetWin32() const {
    return !In64BitMode && (isTargetCygMing() ||
                            isTargetKnownWindowsMSVC());
  }

In practice this broke the JIT tests on 32-bit Windows, which did not
satisfy the new condition:

    LLVM :: ExecutionEngine/MCJIT/2003-01-15-AlignmentTest.ll
    LLVM :: ExecutionEngine/MCJIT/2003-08-15-AllocaAssertion.ll
    LLVM :: ExecutionEngine/MCJIT/2003-08-23-RegisterAllocatePhysReg.ll
    LLVM :: ExecutionEngine/MCJIT/test-loadstore.ll
    LLVM :: ExecutionEngine/OrcMCJIT/2003-01-15-AlignmentTest.ll
    LLVM :: ExecutionEngine/OrcMCJIT/2003-08-15-AllocaAssertion.ll
    LLVM :: ExecutionEngine/OrcMCJIT/2003-08-23-RegisterAllocatePhysReg.ll
    LLVM :: ExecutionEngine/OrcMCJIT/test-loadstore.ll

because %esp was not updated correctly. The failures are only visible
on a MSVC 2017 Debug build, for which we do not have bots.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@306142 91177308-0d34-0410-b5e6-96231b3b80d8

Author: whitequark

lib/Target/X86/X86FrameLowering.cpp

@@ -745,10 +745,13 @@ void X86FrameLowering::emitStackProbeCall(MachineFunction &MF,
       .addReg(SP, RegState::Define | RegState::Implicit)
       .addReg(X86::EFLAGS, RegState::Define | RegState::Implicit);
 
-  if (!STI.isTargetWin32()) {
+  if (STI.isTargetWin64() || !STI.isOSWindows()) {
+    // MSVC x32's _chkstk and cygwin/mingw's _alloca adjust %esp themselves.
     // MSVC x64's __chkstk and cygwin/mingw's ___chkstk_ms do not adjust %rsp
-    // themselves. It also does not clobber %rax so we can reuse it when
+    // themselves. They also does not clobber %rax so we can reuse it when
     // adjusting %rsp.
+    // All other platforms do not specify a particular ABI for the stack probe
+    // function, so we arbitrarily define it to not adjust %esp/%rsp itself.
     BuildMI(MBB, MBBI, DL, TII.get(getSUBrrOpcode(Is64Bit)), SP)
         .addReg(SP)
         .addReg(AX);