[WebAssembly] Enable nontrapping-fptoint and bulk-memory by default. (#112049)

We were prepared to enable these features [back in February], but they
got pulled for what appear to be unrelated reasons. So let's have
another try at enabling them!

Another motivation here is that it'd be convenient for the [Lime1
proposal] if "lime1" is close to a subset of "generic" (missing only
for extended-const).

[back in February]:
https://github.com/WebAssembly/tool-conventions/issues/158#issuecomment-1931119512
[Lime1 proposal]: https://github.com/llvm/llvm-project/pull/112035

1 files changed, 23 insertions, 6 deletions

diff --git a/llvm/lib/Target/WebAssembly/WebAssemblyTargetMachine.cpp b/llvm/lib/Target/WebAssembly/WebAssemblyTargetMachine.cpp
index 3fe6ccf..83cd57d 100644
--- a/llvm/lib/Target/WebAssembly/WebAssemblyTargetMachine.cpp
+++ b/llvm/lib/Target/WebAssembly/WebAssemblyTargetMachine.cpp
@@ -233,13 +233,30 @@ public:
 
 private:
   FeatureBitset coalesceFeatures(const Module &M) {
-    FeatureBitset Features =
-        WasmTM
-            ->getSubtargetImpl(std::string(WasmTM->getTargetCPU()),
-                               std::string(WasmTM->getTargetFeatureString()))
-            ->getFeatureBits();
-    for (auto &F : M)
+    // Union the features of all defined functions. Start with an empty set, so
+    // that if a feature is disabled in every function, we'll compute it as
+    // disabled. If any function lacks a target-features attribute, it'll
+    // default to the target CPU from the `TargetMachine`.
+    FeatureBitset Features;
+    bool AnyDefinedFuncs = false;
+    for (auto &F : M) {
+      if (F.isDeclaration())
+        continue;
+
       Features |= WasmTM->getSubtargetImpl(F)->getFeatureBits();
+      AnyDefinedFuncs = true;
+    }
+
+    // If we have no defined functions, use the target CPU from the
+    // `TargetMachine`.
+    if (!AnyDefinedFuncs) {
+      Features =
+          WasmTM
+              ->getSubtargetImpl(std::string(WasmTM->getTargetCPU()),
+                                 std::string(WasmTM->getTargetFeatureString()))
+              ->getFeatureBits();
+    }
+
     return Features;
   }