[llvm] r220728 - Fix a stackmap bug introduced in r220710.

[Pete Cooper]

Author: pete
Date: Mon Oct 27 17:38:45 2014
New Revision: 220728

URL: http://llvm.org/viewvc/llvm-project?rev=220728&view=rev
Log:
Fix a stackmap bug introduced in r220710.

For a call to not return in to the stackmap shadow, the shadow must end with the call.

To do this, we must insert any required nops *before* the call, and not after it.

Modified:
    llvm/trunk/lib/Target/X86/X86MCInstLower.cpp
    llvm/trunk/test/CodeGen/X86/stackmap-shadow-optimization.ll

Modified: llvm/trunk/lib/Target/X86/X86MCInstLower.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Target/X86/X86MCInstLower.cpp?rev=220728&r1=220727&r2=220728&view=diff
==============================================================================
--- llvm/trunk/lib/Target/X86/X86MCInstLower.cpp (original)
+++ llvm/trunk/lib/Target/X86/X86MCInstLower.cpp Mon Oct 27 17:38:45 2014
@@ -1209,11 +1209,21 @@ void X86AsmPrinter::EmitInstruction(cons
 
   MCInst TmpInst;
   MCInstLowering.Lower(MI, TmpInst);
-  EmitAndCountInstruction(TmpInst);
 
   // Stackmap shadows cannot include branch targets, so we can count the bytes
-  // in a call towards the shadow, but must flush the shadow immediately after
-  // to account for the return from the call.
-  if (MI->isCall())
+  // in a call towards the shadow, but must ensure that the no thread returns
+  // in to the stackmap shadow.  The only way to achieve this is if the call
+  // is at the end of the shadow.
+  if (MI->isCall()) {
+    // Count then size of the call towards the shadow
+    SMShadowTracker.count(TmpInst, getSubtargetInfo());
+    // Then flush the shadow so that we fill with nops before the call, not
+    // after it.
     SMShadowTracker.emitShadowPadding(OutStreamer, getSubtargetInfo());
+    // Then emit the call
+    OutStreamer.EmitInstruction(TmpInst, getSubtargetInfo());
+    return;
+  }
+
+  EmitAndCountInstruction(TmpInst);
 }

Modified: llvm/trunk/test/CodeGen/X86/stackmap-shadow-optimization.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/CodeGen/X86/stackmap-shadow-optimization.ll?rev=220728&r1=220727&r2=220728&view=diff
==============================================================================
--- llvm/trunk/test/CodeGen/X86/stackmap-shadow-optimization.ll (original)
+++ llvm/trunk/test/CodeGen/X86/stackmap-shadow-optimization.ll Mon Oct 27 17:38:45 2014
@@ -5,17 +5,22 @@
 ; bar.  However, the frame teardown and the return do not count towards the
 ; stackmap shadow as the call return counts as a branch target so must flush
 ; the shadow.
+; Note that in order for a thread to not return in to the patched space
+; the call must be at the end of the shadow, so the required nop must be
+; before the call, not after.
 define void @shadow_optimization_test() {
 entry:
 ; CHECK-LABEL:  shadow_optimization_test:
 ; CHECK:        callq   _bar
+; CHECK:        nop
+; CHECK:        callq   _bar
 ; CHECK-NOT:    nop
 ; CHECK:        callq   _bar
-; CHECK:        nop
-; CHECK:        retq
+; CHECK-NOT:    nop
   call void @bar()
   tail call void (i64, i32, ...)* @llvm.experimental.stackmap(i64 0, i32 8)
   call void @bar()
+  call void @bar()
   ret void
 }