[WebAssembly] Fix handling of COPY instructions in WebAssemblyRegStackify.

Move RegStackify after coalescing and teach it to use LiveIntervals instead
of depending on SSA form. This avoids a problem where a register in a COPY
instruction is stackified and then subsequently coalesced with a register
that is not stackified.

This also puts it after the scheduler, which allows us to simplify the
EXPR_STACK constraint, as we no longer have instructions being reordered
after stackification and before coloring.

llvm-svn: 256402

1 files changed, 3 insertions, 6 deletions

diff --git a/llvm/lib/Target/WebAssembly/WebAssemblyTargetMachine.cpp b/llvm/lib/Target/WebAssembly/WebAssemblyTargetMachine.cpp
index c774c120bb5..e31ea46de9f 100644
--- a/llvm/lib/Target/WebAssembly/WebAssemblyTargetMachine.cpp
+++ b/llvm/lib/Target/WebAssembly/WebAssemblyTargetMachine.cpp
@@ -165,12 +165,6 @@ void WebAssemblyPassConfig::addPreRegAlloc() {
 
   // Prepare store instructions for register stackifying.
   addPass(createWebAssemblyStoreResults());
-
-  // Mark registers as representing wasm's expression stack.
-  addPass(createWebAssemblyRegStackify());
-  // The register coalescing pass has a bad interaction with COPY MIs which have
-  // EXPR_STACK as an extra operand
-  // disablePass(&RegisterCoalescerID);
 }
 
 void WebAssemblyPassConfig::addPostRegAlloc() {
@@ -184,6 +178,9 @@ void WebAssemblyPassConfig::addPostRegAlloc() {
   // Fails with: should be run after register allocation.
   disablePass(&MachineCopyPropagationID);
 
+  // Mark registers as representing wasm's expression stack.
+  addPass(createWebAssemblyRegStackify());
+
   // Run the register coloring pass to reduce the total number of registers.
   addPass(createWebAssemblyRegColoring());