[llvm] r261039 - [X86] Fix a shrink-wrapping miscompile around __chkstk

[Reid Kleckner via llvm-commits]

Author: rnk
Date: Tue Feb 16 18:17:33 2016
New Revision: 261039

URL: http://llvm.org/viewvc/llvm-project?rev=261039&view=rev
Log:
[X86] Fix a shrink-wrapping miscompile around __chkstk

__chkstk clobbers EAX. If EAX is live across the prologue, then we have
to take extra steps to save it. We already had code to do this if EAX
was a register parameter. This change adapts it to work when shrink
wrapping is used.

Modified:
    llvm/trunk/lib/Target/X86/X86FrameLowering.cpp
    llvm/trunk/test/CodeGen/X86/shrink-wrap-chkstk.ll

Modified: llvm/trunk/lib/Target/X86/X86FrameLowering.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Target/X86/X86FrameLowering.cpp?rev=261039&r1=261038&r2=261039&view=diff
==============================================================================
--- llvm/trunk/lib/Target/X86/X86FrameLowering.cpp (original)
+++ llvm/trunk/lib/Target/X86/X86FrameLowering.cpp Tue Feb 16 18:17:33 2016
@@ -192,10 +192,9 @@ static unsigned findDeadCallerSavedReg(M
   return 0;
 }
 
-static bool isEAXLiveIn(MachineFunction &MF) {
-  for (MachineRegisterInfo::livein_iterator II = MF.getRegInfo().livein_begin(),
-       EE = MF.getRegInfo().livein_end(); II != EE; ++II) {
-    unsigned Reg = II->first;
+static bool isEAXLiveIn(MachineBasicBlock &MBB) {
+  for (MachineBasicBlock::RegisterMaskPair RegMask : MBB.liveins()) {
+    unsigned Reg = RegMask.PhysReg;
 
     if (Reg == X86::RAX || Reg == X86::EAX || Reg == X86::AX ||
         Reg == X86::AH || Reg == X86::AL)
@@ -261,7 +260,7 @@ void X86FrameLowering::emitSPUpdate(Mach
       // load the offset into a register and do one sub/add
       unsigned Reg = 0;
 
-      if (isSub && !isEAXLiveIn(*MBB.getParent()))
+      if (isSub && !isEAXLiveIn(MBB))
         Reg = (unsigned)(Is64Bit ? X86::RAX : X86::EAX);
       else
         Reg = findDeadCallerSavedReg(MBB, MBBI, TRI, Is64Bit);
@@ -1138,8 +1137,8 @@ void X86FrameLowering::emitPrologue(Mach
   if (IsWin64Prologue && !IsFunclet && TRI->needsStackRealignment(MF))
     AlignedNumBytes = alignTo(AlignedNumBytes, MaxAlign);
   if (AlignedNumBytes >= StackProbeSize && UseStackProbe) {
-    // Check whether EAX is livein for this function.
-    bool isEAXAlive = isEAXLiveIn(MF);
+    // Check whether EAX is livein for this block.
+    bool isEAXAlive = isEAXLiveIn(MBB);
 
     if (isEAXAlive) {
       // Sanity check that EAX is not livein for this function.

Modified: llvm/trunk/test/CodeGen/X86/shrink-wrap-chkstk.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/CodeGen/X86/shrink-wrap-chkstk.ll?rev=261039&r1=261038&r2=261039&view=diff
==============================================================================
--- llvm/trunk/test/CodeGen/X86/shrink-wrap-chkstk.ll (original)
+++ llvm/trunk/test/CodeGen/X86/shrink-wrap-chkstk.ll Tue Feb 16 18:17:33 2016
@@ -1,6 +1,8 @@
 ; RUN: llc < %s -enable-shrink-wrap=true | FileCheck %s
 
 ; chkstk cannot come before the usual prologue, since it adjusts ESP.
+; If chkstk is used in the prologue, we also have to be careful about preserving
+; EAX if it is used.
 
 target datalayout = "e-m:x-p:32:32-i64:64-f80:32-n8:16:32-a:0:32-S32"
 target triple = "i686-pc-windows-msvc18.0.0"
@@ -35,3 +37,36 @@ bb2:
 ; CHECK: retl
 
 declare void @inalloca_params(<{ %struct.S }>* inalloca)
+
+declare i32 @doSomething(i32, i32*)
+
+; In this test case, we force usage of EAX before the prologue, and have to
+; compensate before calling __chkstk. It would also be valid for us to avoid
+; shrink wrapping in this case.
+
+define x86_fastcallcc i32 @use_eax_before_prologue(i32 inreg %a, i32 inreg %b) {
+  %tmp = alloca i32, i32 1024, align 4
+  %tmp2 = icmp slt i32 %a, %b
+  br i1 %tmp2, label %true, label %false
+
+true:
+  store i32 %a, i32* %tmp, align 4
+  %tmp4 = call i32 @doSomething(i32 0, i32* %tmp)
+  br label %false
+
+false:
+  %tmp.0 = phi i32 [ %tmp4, %true ], [ %a, %0 ]
+  ret i32 %tmp.0
+}
+
+; CHECK-LABEL: @use_eax_before_prologue at 8: # @use_eax_before_prologue
+; CHECK: movl %ecx, %eax
+; CHECK: cmpl %edx, %eax
+; CHECK: jge LBB1_2
+; CHECK: pushl %eax
+; CHECK: movl $4100, %eax
+; CHECK: calll __chkstk
+; CHECK: movl 4100(%esp), %eax
+; CHECK: calll _doSomething
+; CHECK: LBB1_2:
+; CHECK: retl