[X86] Optimize stackmap shadows on X86.

This patch minimizes the number of nops that must be emitted on X86 to satisfy
stackmap shadow constraints.

To minimize the number of nops inserted, the X86AsmPrinter now records the
size of the most recent stackmap's shadow in the StackMapShadowTracker class,
and tracks the number of instruction bytes emitted since the that stackmap
instruction was encountered. Padding is emitted (if it is required at all)
immediately before the next stackmap/patchpoint instruction, or at the end of
the basic block.

This optimization should reduce code-size and improve performance for people
using the llvm stackmap intrinsic on X86.

<rdar://problem/14959522>

llvm-svn: 213892

1 files changed, 21 insertions, 0 deletions

diff --git a/llvm/test/CodeGen/X86/stackmap-shadow-optimization.ll b/llvm/test/CodeGen/X86/stackmap-shadow-optimization.ll
new file mode 100644
index 00000000000..63debe396b6
--- /dev/null
+++ b/llvm/test/CodeGen/X86/stackmap-shadow-optimization.ll
@@ -0,0 +1,21 @@
+; RUN: llc < %s -mtriple=x86_64-apple-darwin -mcpu=corei7 -disable-fp-elim | FileCheck %s
+
+; Check that the X86 stackmap shadow optimization is only outputting a 1-byte
+; nop here. 8-bytes are requested, but 7 are covered by the code for the call to
+; bar, the frame teardown and the return.
+define void @shadow_optimization_test() {
+entry:
+; CHECK-LABEL:  shadow_optimization_test:
+; CHECK:        callq   _bar
+; CHECK-NOT:    nop
+; CHECK:        callq   _bar
+; CHECK:        retq
+; CHECK:        nop
+  call void @bar()
+  tail call void (i64, i32, ...)* @llvm.experimental.stackmap(i64 0, i32 8)
+  call void @bar()
+  ret void
+}
+
+declare void @llvm.experimental.stackmap(i64, i32, ...)
+declare void @bar()
\ No newline at end of file