[WebAssembly] Move register stackification and coloring to a late phase.

Move the register stackification and coloring passes to run very late, after
PEI, tail duplication, and most other passes. This means that all code emitted
and expanded by those passes is now exposed to these passes. This also
eliminates the need for prologue/epilogue code to be manually stackified,
which significantly simplifies the code.

This does require running LiveIntervals a second time. It's useful to think
of these late passes not as late optimization passes, but as a domain-specific
compression algorithm based on knowledge of liveness information. It's used to
compress the code after all conventional optimizations are complete, which is
why it uses LiveIntervals at a phase when actual optimization passes don't
typically need it.

Differential Revision: http://reviews.llvm.org/D20075

llvm-svn: 269012

1 files changed, 27 insertions, 23 deletions

diff --git a/llvm/lib/Target/WebAssembly/WebAssemblyTargetMachine.cpp b/llvm/lib/Target/WebAssembly/WebAssemblyTargetMachine.cpp
index dd3431b96709..472e0d36273a 100644
--- a/llvm/lib/Target/WebAssembly/WebAssemblyTargetMachine.cpp
+++ b/llvm/lib/Target/WebAssembly/WebAssemblyTargetMachine.cpp
@@ -103,8 +103,6 @@ public:
 
   void addIRPasses() override;
   bool addInstSelector() override;
-  bool addILPOpts() override;
-  void addPreRegAlloc() override;
   void addPostRegAlloc() override;
   bool addGCPasses() override { return false; }
   void addPreEmitPass() override;
@@ -162,19 +160,6 @@ bool WebAssemblyPassConfig::addInstSelector() {
   return false;
 }
 
-bool WebAssemblyPassConfig::addILPOpts() {
-  (void)TargetPassConfig::addILPOpts();
-  return true;
-}
-
-void WebAssemblyPassConfig::addPreRegAlloc() {
-  TargetPassConfig::addPreRegAlloc();
-
-  // Prepare store instructions for register stackifying.
-  if (getOptLevel() != CodeGenOpt::None)
-    addPass(createWebAssemblyStoreResults());
-}
-
 void WebAssemblyPassConfig::addPostRegAlloc() {
   // TODO: The following CodeGen passes don't currently support code containing
   // virtual registers. Consider removing their restrictions and re-enabling
@@ -194,14 +179,6 @@ void WebAssemblyPassConfig::addPostRegAlloc() {
   disablePass(&LiveDebugValuesID);
   disablePass(&PatchableFunctionID);
 
-  if (getOptLevel() != CodeGenOpt::None) {
-    // Mark registers as representing wasm's expression stack.
-    addPass(createWebAssemblyRegStackify());
-
-    // Run the register coloring pass to reduce the total number of registers.
-    addPass(createWebAssemblyRegColoring());
-  }
-
   TargetPassConfig::addPostRegAlloc();
 
   // Run WebAssembly's version of the PrologEpilogInserter. Target-independent
@@ -213,6 +190,33 @@ void WebAssemblyPassConfig::addPostRegAlloc() {
 void WebAssemblyPassConfig::addPreEmitPass() {
   TargetPassConfig::addPreEmitPass();
 
+  // Now that we have a prologue and epilogue and all frame indices are
+  // rewritten, eliminate SP and FP. This allows them to be stackified,
+  // colored, and numbered with the rest of the registers.
+  addPass(createWebAssemblyReplacePhysRegs());
+
+  if (getOptLevel() != CodeGenOpt::None) {
+    // LiveIntervals isn't commonly run this late. Re-establish preconditions.
+    addPass(createWebAssemblyPrepareForLiveIntervals());
+
+    // Depend on LiveIntervals and perform some optimizations on it.
+    addPass(createWebAssemblyOptimizeLiveIntervals());
+
+    // Prepare store instructions for register stackifying.
+    addPass(createWebAssemblyStoreResults());
+
+    // Mark registers as representing wasm's expression stack. This is a key
+    // code-compression technique in WebAssembly. We run this pass (and
+    // StoreResults above) very late, so that it sees as much code as possible,
+    // including code emitted by PEI and expanded by late tail duplication.
+    addPass(createWebAssemblyRegStackify());
+
+    // Run the register coloring pass to reduce the total number of registers.
+    // This runs after stackification so that it doesn't consider registers
+    // that become stackified.
+    addPass(createWebAssemblyRegColoring());
+  }
+
   // Eliminate multiple-entry loops.
   addPass(createWebAssemblyFixIrreducibleControlFlow());