Fix nasty mingw32 bug, which e.g. prevented llvm-gcc bootstrap there.

Mark _alloca call as clobberring EFLAGS, otherwise some DCE might remove
other flags-clobberring stuff (e.g. cmp instructions) occuring after
_alloca call.

llvm-svn: 112034

Author: asl

llvm/lib/Target/X86/X86ISelLowering.cpp

@@ -8930,7 +8930,8 @@ X86TargetLowering::EmitLoweredMingwAlloca(MachineInstr *MI,
     .addReg(X86::EAX, RegState::Implicit)
     .addReg(X86::ESP, RegState::Implicit)
     .addReg(X86::EAX, RegState::Define | RegState::Implicit)
-    .addReg(X86::ESP, RegState::Define | RegState::Implicit);
+    .addReg(X86::ESP, RegState::Define | RegState::Implicit)
+    .addReg(X86::EFLAGS, RegState::Define | RegState::Implicit);
 
   MI->eraseFromParent();   // The pseudo instruction is gone now.
   return BB;

llvm/lib/Target/X86/X86InstrInfo.td

@@ -580,9 +580,10 @@ def VASTART_SAVE_XMM_REGS : I<0, Pseudo,
 // The main point of having separate instruction are extra unmodelled effects
 // (compared to ordinary calls) like stack pointer change.
 
-def MINGW_ALLOCA : I<0, Pseudo, (outs), (ins),
-                     "# dynamic stack allocation",
-                     [(X86MingwAlloca)]>;
+let Defs = [EAX, ESP, EFLAGS], Uses = [ESP] in
+  def MINGW_ALLOCA : I<0, Pseudo, (outs), (ins),
+                       "# dynamic stack allocation",
+                       [(X86MingwAlloca)]>;
 }
 
 // Nop

llvm/lib/Target/X86/X86RegisterInfo.cpp

@@ -1109,7 +1109,8 @@ void X86RegisterInfo::emitPrologue(MachineFunction &MF) const {
         .addImm(NumBytes);
       BuildMI(MBB, MBBI, DL, TII.get(X86::CALLpcrel32))
         .addExternalSymbol("_alloca")
-        .addReg(StackPtr, RegState::Define | RegState::Implicit);
+        .addReg(StackPtr,    RegState::Define | RegState::Implicit)
+        .addReg(X86::EFLAGS, RegState::Define | RegState::Implicit);
     } else {
       // Save EAX
       BuildMI(MBB, MBBI, DL, TII.get(X86::PUSH32r))
@@ -1121,7 +1122,8 @@ void X86RegisterInfo::emitPrologue(MachineFunction &MF) const {
         .addImm(NumBytes - 4);
       BuildMI(MBB, MBBI, DL, TII.get(X86::CALLpcrel32))
         .addExternalSymbol("_alloca")
-        .addReg(StackPtr, RegState::Define | RegState::Implicit);
+        .addReg(StackPtr,    RegState::Define | RegState::Implicit)
+        .addReg(X86::EFLAGS, RegState::Define | RegState::Implicit);
 
       // Restore EAX
       MachineInstr *MI = addRegOffset(BuildMI(MF, DL, TII.get(X86::MOV32rm),