[WebAssembly] Add some more ideas to README.txt.

[oota-llvm.git] / lib / Target / WebAssembly / README.txt

diff --git a/lib/Target/WebAssembly/README.txt b/lib/Target/WebAssembly/README.txt
index 8604528b2fc8e4c157f3429e363762219a473f92..97072ab1cc156a41d530402f2ba8edc335758486 100644 (file)
--- a/lib/Target/WebAssembly/README.txt
+++ b/lib/Target/WebAssembly/README.txt
@@ -12,6 +12,15 @@ binary encoding of WebAssembly itself:
   * https://github.com/WebAssembly/design/blob/master/AstSemantics.md
   * https://github.com/WebAssembly/design/blob/master/BinaryEncoding.md
 
+The backend is built, tested and archived on the following waterfall:
+  https://build.chromium.org/p/client.wasm.llvm/console
+
+The backend's bringup is done using the GCC torture test suite first since it
+doesn't require C library support. Current known failures are in
+known_gcc_test_failures.txt, all other tests should pass. The waterfall will
+turn red if not. Once most of these pass, further testing will use LLVM's own
+test suite.
+
 Interesting work that remains to be done:
 * Write a pass to restructurize irreducible control flow. This needs to be done
   before register allocation to be efficient, because it may duplicate basic
@@ -22,7 +31,7 @@ Interesting work that remains to be done:
 
 //===---------------------------------------------------------------------===//
 
-set_local and store instructions have a return value. We should (a) model this,
+set_local instructions have a return value. We should (a) model this,
 and (b) write optimizations which take advantage of it. Keep in mind that
 many set_local instructions are implicit!
 
@@ -38,3 +47,46 @@ expression stack across the jump (sometimes). We should (a) model this, and
 (b) extend the stackifier to utilize it.
 
 //===---------------------------------------------------------------------===//
+
+The min/max operators aren't exactly a<b?a:b because of NaN and negative zero
+behavior. The ARM target has the same kind of min/max instructions and has
+implemented optimizations for them; we should do similar optimizations for
+WebAssembly.
+
+//===---------------------------------------------------------------------===//
+
+AArch64 runs SeparateConstOffsetFromGEPPass, followed by EarlyCSE and LICM.
+Would these be useful to run for WebAssembly too? Also, it has an option to
+run SimplifyCFG after running the AtomicExpand pass. Would this be useful for
+us too?
+
+//===---------------------------------------------------------------------===//
+
+When is it profitable to set isAsCheapAsAMove on instructions in WebAssembly?
+
+//===---------------------------------------------------------------------===//
+
+Register stackification uses the EXPR_STACK physical register to impose
+ordering dependencies on instructions with stack operands. This is pessimistic;
+we should consider alternate ways to model stack dependencies.
+
+//===---------------------------------------------------------------------===//
+
+Lots of things could be done in WebAssemblyTargetTransformInfo.cpp. Similarly,
+there are numerous optimization-related hooks that can be overridden in
+WebAssemblyTargetLowering.
+
+//===---------------------------------------------------------------------===//
+
+Instead of the OptimizeReturned pass, which should consider preserving the
+"returned" attribute through to MachineInstrs and extending the StoreResults
+pass to do this optimization on calls too. That would also let the
+WebAssemblyPeephole pass clean up dead defs for such calls, as it does for
+stores.
+
+//===---------------------------------------------------------------------===//
+
+Memset/memcpy/memmove should be marked with the "returned" attribute somehow,
+even when they are translated through intrinsics.
+
+//===---------------------------------------------------------------------===//