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.
llvm-svn: 220728
diff --git a/llvm/lib/Target/X86/X86MCInstLower.cpp b/llvm/lib/Target/X86/X86MCInstLower.cpp
index 85cf514..4e0d594 100644
--- a/llvm/lib/Target/X86/X86MCInstLower.cpp
+++ b/llvm/lib/Target/X86/X86MCInstLower.cpp
@@ -1209,11 +1209,21 @@
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);
}
diff --git a/llvm/test/CodeGen/X86/stackmap-shadow-optimization.ll b/llvm/test/CodeGen/X86/stackmap-shadow-optimization.ll
index f640b9e..a3725f2 100644
--- a/llvm/test/CodeGen/X86/stackmap-shadow-optimization.ll
+++ b/llvm/test/CodeGen/X86/stackmap-shadow-optimization.ll
@@ -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
}