[WebAssembly] Disable the MachineScheduler.

llvm-svn: 269976

llvm/lib/Target/WebAssembly/README.txt

@@ -128,3 +128,10 @@ has two operands and one result, so in such cases there could be a net win by
 prefering the operands.
 
 //===---------------------------------------------------------------------===//
+
+Instruction ordering has a significant influence on register stackification and
+coloring. Consider experimenting with the MachineScheduler (enable via
+enableMachineScheduler) and determine if it can be configured to schedule
+instructions advantageously for this purpose.
+
+//===---------------------------------------------------------------------===//

llvm/lib/Target/WebAssembly/WebAssemblySubtarget.cpp

@@ -45,5 +45,11 @@ WebAssemblySubtarget::WebAssemblySubtarget(const Triple &TT,
       InstrInfo(initializeSubtargetDependencies(FS)), TSInfo(),
       TLInfo(TM, *this) {}
 
-bool WebAssemblySubtarget::enableMachineScheduler() const { return true; }
+bool WebAssemblySubtarget::enableMachineScheduler() const {
+  // Disable the MachineScheduler for now. Even with ShouldTrackPressure set and
+  // enableMachineSchedDefaultSched overridden, it appears to have an overall
+  // negative effect for the kinds of register optimizations we're doing.
+  return false;
+}
+
 bool WebAssemblySubtarget::useAA() const { return true; }