Fix for PR30687. Avoid dereferencing MBB.end().

We don't need to return a MachineInstr* from these stack probe insertion
calls anyway. If we ever need to add it back, we can return an iterator
instead.

Based on a patch by David Kreitzer

This bug is a consequence of

r279314 | dexonsmith | 2016-08-19 13:40:12 -0700 (Fri, 19 Aug 2016) | 110 lines

We hit the "Assertion `!NodePtr->isKnownSentinel()' failed" assertion,
but only when inserting a stack probe call at the end of an MBB, which
isn't necessarily a common situation.

Differential Revision: https://reviews.llvm.org/D25566

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@284130 91177308-0d34-0410-b5e6-96231b3b80d8

lib/Target/X86/X86FrameLowering.cpp

@@ -447,20 +447,19 @@ void X86FrameLowering::emitCalleeSavedFrameMoves(
   }
 }
 
-MachineInstr *X86FrameLowering::emitStackProbe(MachineFunction &MF,
-                                               MachineBasicBlock &MBB,
-                                               MachineBasicBlock::iterator MBBI,
-                                               const DebugLoc &DL,
-                                               bool InProlog) const {
+void X86FrameLowering::emitStackProbe(MachineFunction &MF,
+                                      MachineBasicBlock &MBB,
+                                      MachineBasicBlock::iterator MBBI,
+                                      const DebugLoc &DL, bool InProlog) const {
   const X86Subtarget &STI = MF.getSubtarget<X86Subtarget>();
   if (STI.isTargetWindowsCoreCLR()) {
     if (InProlog) {
-      return emitStackProbeInlineStub(MF, MBB, MBBI, DL, true);
+      emitStackProbeInlineStub(MF, MBB, MBBI, DL, true);
     } else {
-      return emitStackProbeInline(MF, MBB, MBBI, DL, false);
+      emitStackProbeInline(MF, MBB, MBBI, DL, false);
     }
   } else {
-    return emitStackProbeCall(MF, MBB, MBBI, DL, InProlog);
+    emitStackProbeCall(MF, MBB, MBBI, DL, InProlog);
   }
 }
 
@@ -489,9 +488,11 @@ void X86FrameLowering::inlineStackProbe(MachineFunction &MF,
   }
 }
 
-MachineInstr *X86FrameLowering::emitStackProbeInline(
-    MachineFunction &MF, MachineBasicBlock &MBB,
-    MachineBasicBlock::iterator MBBI, const DebugLoc &DL, bool InProlog) const {
+void X86FrameLowering::emitStackProbeInline(MachineFunction &MF,
+                                            MachineBasicBlock &MBB,
+                                            MachineBasicBlock::iterator MBBI,
+                                            const DebugLoc &DL,
+                                            bool InProlog) const {
   const X86Subtarget &STI = MF.getSubtarget<X86Subtarget>();
   assert(STI.is64Bit() && "different expansion needed for 32 bit");
   assert(STI.isTargetWindowsCoreCLR() && "custom expansion expects CoreCLR");
@@ -701,13 +702,13 @@ MachineInstr *X86FrameLowering::emitStackProbeInline(
   }
 
   // Possible TODO: physreg liveness for InProlog case.
-
-  return &*ContinueMBBI;
 }
 
-MachineInstr *X86FrameLowering::emitStackProbeCall(
-    MachineFunction &MF, MachineBasicBlock &MBB,
-    MachineBasicBlock::iterator MBBI, const DebugLoc &DL, bool InProlog) const {
+void X86FrameLowering::emitStackProbeCall(MachineFunction &MF,
+                                          MachineBasicBlock &MBB,
+                                          MachineBasicBlock::iterator MBBI,
+                                          const DebugLoc &DL,
+                                          bool InProlog) const {
   bool IsLargeCodeModel = MF.getTarget().getCodeModel() == CodeModel::Large;
 
   unsigned CallOp;
@@ -765,20 +766,16 @@ MachineInstr *X86FrameLowering::emitStackProbeCall(
     for (++ExpansionMBBI; ExpansionMBBI != MBBI; ++ExpansionMBBI)
       ExpansionMBBI->setFlag(MachineInstr::FrameSetup);
   }
-
-  return &*MBBI;
 }
 
-MachineInstr *X86FrameLowering::emitStackProbeInlineStub(
+void X86FrameLowering::emitStackProbeInlineStub(
     MachineFunction &MF, MachineBasicBlock &MBB,
     MachineBasicBlock::iterator MBBI, const DebugLoc &DL, bool InProlog) const {
 
   assert(InProlog && "ChkStkStub called outside prolog!");
 
   BuildMI(MBB, MBBI, DL, TII.get(X86::CALLpcrel32))
       .addExternalSymbol("__chkstk_stub");
-
-  return &*MBBI;
 }
 
 static unsigned calculateSetFPREG(uint64_t SPAdjust) {

lib/Target/X86/X86FrameLowering.h

@@ -49,11 +49,10 @@ class X86FrameLowering : public TargetFrameLowering {
 
   /// Emit target stack probe code. This is required for all
   /// large stack allocations on Windows. The caller is required to materialize
-  /// the number of bytes to probe in RAX/EAX. Returns instruction just
-  /// after the expansion.
-  MachineInstr *emitStackProbe(MachineFunction &MF, MachineBasicBlock &MBB,
-                               MachineBasicBlock::iterator MBBI,
-                               const DebugLoc &DL, bool InProlog) const;
+  /// the number of bytes to probe in RAX/EAX.
+  void emitStackProbe(MachineFunction &MF, MachineBasicBlock &MBB,
+                      MachineBasicBlock::iterator MBBI, const DebugLoc &DL,
+                      bool InProlog) const;
 
   /// Replace a StackProbe inline-stub with the actual probe code inline.
   void inlineStackProbe(MachineFunction &MF,
@@ -179,22 +178,19 @@ class X86FrameLowering : public TargetFrameLowering {
   uint64_t calculateMaxStackAlign(const MachineFunction &MF) const;
 
   /// Emit target stack probe as a call to a helper function
-  MachineInstr *emitStackProbeCall(MachineFunction &MF, MachineBasicBlock &MBB,
-                                   MachineBasicBlock::iterator MBBI,
-                                   const DebugLoc &DL, bool InProlog) const;
+  void emitStackProbeCall(MachineFunction &MF, MachineBasicBlock &MBB,
+                          MachineBasicBlock::iterator MBBI, const DebugLoc &DL,
+                          bool InProlog) const;
 
   /// Emit target stack probe as an inline sequence.
-  MachineInstr *emitStackProbeInline(MachineFunction &MF,
-                                     MachineBasicBlock &MBB,
-                                     MachineBasicBlock::iterator MBBI,
-                                     const DebugLoc &DL, bool InProlog) const;
+  void emitStackProbeInline(MachineFunction &MF, MachineBasicBlock &MBB,
+                            MachineBasicBlock::iterator MBBI,
+                            const DebugLoc &DL, bool InProlog) const;
 
   /// Emit a stub to later inline the target stack probe.
-  MachineInstr *emitStackProbeInlineStub(MachineFunction &MF,
-                                         MachineBasicBlock &MBB,
-                                         MachineBasicBlock::iterator MBBI,
-                                         const DebugLoc &DL,
-                                         bool InProlog) const;
+  void emitStackProbeInlineStub(MachineFunction &MF, MachineBasicBlock &MBB,
+                                MachineBasicBlock::iterator MBBI,
+                                const DebugLoc &DL, bool InProlog) const;
 
   /// Aligns the stack pointer by ANDing it with -MaxAlign.
   void BuildStackAlignAND(MachineBasicBlock &MBB,

test/CodeGen/X86/win_chkstk.ll

@@ -63,3 +63,20 @@ entry:
   %array4096 = alloca [4096 x i8], align 16       ; <[4096 x i8]*> [#uses=0]
   ret i32 0
 }
+
+; PR30687: Avoid crashing when inserting a __chkstk call at the end of an MBB.
+define void @dont_crash() {
+entry:
+; WIN_X32:    calll __chkstk
+; WIN_X64:    callq __chkstk
+; WIN64_LARGE: movabsq $__chkstk, %r11
+; WIN64_LARGE: callq *%r11
+; MINGW_X32:  calll __alloca
+; MINGW_X64:  callq ___chkstk_ms
+; LINUX-NOT:  call __chkstk
+  %buffer = alloca [4096 x i8]
+  br label %ret
+
+ret:
+  ret void
+}