[WebAssembly] Implement prolog/epilog insertion and FrameIndex elimination

Summary:
Use the SP32 physical register as the base for FrameIndex
lowering. Update it and the __stack_pointer global var in the prolog and
epilog. Extend the mapping of virtual registers to wasm locals to
include the physical registers.

Rather than modify the target-independent PrologEpilogInserter (which
asserts that there are no virtual registers left) include a
slightly-modified copy for Wasm that does not have this assertion and
only clears the virtual registers if scavenging was needed (which of
course it isn't for wasm).

Differential Revision: http://reviews.llvm.org/D15344

llvm-svn: 255392

1 files changed, 7 insertions, 1 deletions

diff --git a/llvm/lib/Target/WebAssembly/WebAssemblyTargetMachine.cpp b/llvm/lib/Target/WebAssembly/WebAssemblyTargetMachine.cpp
index a333fb3055e..dcc393db6ea 100644
--- a/llvm/lib/Target/WebAssembly/WebAssemblyTargetMachine.cpp
+++ b/llvm/lib/Target/WebAssembly/WebAssemblyTargetMachine.cpp
@@ -176,7 +176,8 @@ void WebAssemblyPassConfig::addPostRegAlloc() {
   // virtual registers. Consider removing their restrictions and re-enabling
   // them.
   //
-  // Fails with: Regalloc must assign all vregs.
+  // We use our own PrologEpilogInserter which is very slightly modified to
+  // tolerate virtual registers.
   disablePass(&PrologEpilogCodeInserterID);
   // Fails with: should be run after register allocation.
   disablePass(&MachineCopyPropagationID);
@@ -185,6 +186,11 @@ void WebAssemblyPassConfig::addPostRegAlloc() {
   addPass(createWebAssemblyRegColoring());
 
   TargetPassConfig::addPostRegAlloc();
+
+  // Run WebAssembly's version of the PrologEpilogInserter. Target-independent
+  // PEI runs after PostRegAlloc and after ShrinkWrap. Putting it here will run
+  // PEI before ShrinkWrap but otherwise in the same position in the order.
+  addPass(createWebAssemblyPEI());
 }
 
 void WebAssemblyPassConfig::addPreEmitPass() {