[WebAssembly] Use a physical register to describe ARGUMENT liveness.
Instead of trying to move ARGUMENT instructions back up to the top after
they've been scheduled or sunk down, use a fake physical register to
create a liveness constraint that prevents ARGUMENT instructions from
moving down in the first place. This is still not entirely ideal, however
it is more robust than letting them move and moving them back.
llvm-svn: 254084
diff --git a/llvm/lib/Target/WebAssembly/WebAssemblyISelLowering.cpp b/llvm/lib/Target/WebAssembly/WebAssemblyISelLowering.cpp
index 405a2a9..5a3e021 100644
--- a/llvm/lib/Target/WebAssembly/WebAssemblyISelLowering.cpp
+++ b/llvm/lib/Target/WebAssembly/WebAssemblyISelLowering.cpp
@@ -377,6 +377,10 @@
if (IsVarArg)
fail(DL, DAG, "WebAssembly doesn't support varargs yet");
+ // Set up the incoming ARGUMENTS value, which serves to represent the liveness
+ // of the incoming values before they're represented by virtual registers.
+ MF.getRegInfo().addLiveIn(WebAssembly::ARGUMENTS);
+
for (const ISD::InputArg &In : Ins) {
if (In.Flags.isByVal())
fail(DL, DAG, "WebAssembly hasn't implemented byval arguments");