[llvm] 4f1244d - [WebAssembly] Nullify unnecessary setjmp invokes

[Heejin Ahn via llvm-commits]

Author: Heejin Ahn
Date: 2022-01-27T21:11:10-08:00
New Revision: 4f1244d7ccb8a9d1c932e2a7d883d0cd1da9650d

URL: https://github.com/llvm/llvm-project/commit/4f1244d7ccb8a9d1c932e2a7d883d0cd1da9650d
DIFF: https://github.com/llvm/llvm-project/commit/4f1244d7ccb8a9d1c932e2a7d883d0cd1da9650d.diff

LOG: [WebAssembly] Nullify unnecessary setjmp invokes

This is similar to D116619, but now it handles `invoke`s. The reason we
didn't handle `invoke`s back then was we didn't support Wasm EH + Wasm
SjLj together, and the only case SjLj transformation will see `invoke`s
is when we are using Wasm EH. (In Emscripten EH, they would have been
transformed to `call`s to invoke wrappers.)

But after D117610 we support Wasm EH + Wasm SjLj together and we can
nullify `invoke`s to `setjmp` when there is no other longjmpable calls
within the function. Actually this is very unlikely to happen in
practice, because we treat destructors as longjmpable and also treat
`__cxa_end_catch` as longjmpable even if it is not.

Reviewed By: dschuff

Differential Revision: https://reviews.llvm.org/D118408

Added: 
    

Modified: 
    llvm/lib/Target/WebAssembly/WebAssemblyLowerEmscriptenEHSjLj.cpp
    llvm/test/CodeGen/WebAssembly/lower-em-sjlj.ll
    llvm/test/CodeGen/WebAssembly/lower-wasm-ehsjlj.ll

Removed: 
    


################################################################################
diff  --git a/llvm/lib/Target/WebAssembly/WebAssemblyLowerEmscriptenEHSjLj.cpp b/llvm/lib/Target/WebAssembly/WebAssemblyLowerEmscriptenEHSjLj.cpp
index 7dbb53a2bcd5..8a63c7c893dc 100644
--- a/llvm/lib/Target/WebAssembly/WebAssemblyLowerEmscriptenEHSjLj.cpp
+++ b/llvm/lib/Target/WebAssembly/WebAssemblyLowerEmscriptenEHSjLj.cpp
@@ -874,15 +874,17 @@ static void nullifySetjmp(Function *F) {
   Function *SetjmpF = M.getFunction("setjmp");
   SmallVector<Instruction *, 1> ToErase;
 
-  for (User *U : SetjmpF->users()) {
-    auto *CI = dyn_cast<CallInst>(U);
-    // FIXME 'invoke' to setjmp can happen when we use Wasm EH + Wasm SjLj, but
-    // we don't support two being used together yet.
-    if (!CI)
-      report_fatal_error("Wasm EH + Wasm SjLj is not fully supported yet");
-    BasicBlock *BB = CI->getParent();
+  for (User *U : make_early_inc_range(SetjmpF->users())) {
+    auto *CB = dyn_cast<CallBase>(U);
+    BasicBlock *BB = CB->getParent();
     if (BB->getParent() != F) // in other function
       continue;
+    CallInst *CI = nullptr;
+    // setjmp cannot throw. So if it is an invoke, lower it to a call
+    if (auto *II = dyn_cast<InvokeInst>(CB))
+      CI = llvm::changeToCall(II);
+    else
+      CI = cast<CallInst>(CB);
     ToErase.push_back(CI);
     CI->replaceAllUsesWith(IRB.getInt32(0));
   }

diff  --git a/llvm/test/CodeGen/WebAssembly/lower-em-sjlj.ll b/llvm/test/CodeGen/WebAssembly/lower-em-sjlj.ll
index 77dcff2e0799..57612f687afd 100644
--- a/llvm/test/CodeGen/WebAssembly/lower-em-sjlj.ll
+++ b/llvm/test/CodeGen/WebAssembly/lower-em-sjlj.ll
@@ -140,10 +140,13 @@ entry:
   ; free cannot longjmp
   call void @free(i8* %ptr)
   ret i32 %call
+; CHECK: entry:
 ; CHECK-NOT: @malloc
 ; CHECK-NOT: %setjmpTable
 ; CHECK-NOT: @saveSetjmp
 ; CHECK-NOT: @testSetjmp
+; The remaining setjmp call is converted to constant 0, because setjmp returns 0
+; when called directly.
 ; CHECK: ret i32 0
 }
 

diff  --git a/llvm/test/CodeGen/WebAssembly/lower-wasm-ehsjlj.ll b/llvm/test/CodeGen/WebAssembly/lower-wasm-ehsjlj.ll
index ae5cb68ff835..446c298865ad 100644
--- a/llvm/test/CodeGen/WebAssembly/lower-wasm-ehsjlj.ll
+++ b/llvm/test/CodeGen/WebAssembly/lower-wasm-ehsjlj.ll
@@ -271,6 +271,29 @@ ehcleanup:                                        ; preds = %entry
   cleanupret from %0 unwind to caller
 }
 
+; This case was adapted from @cleanuppad_no_parent by removing allocas and
+; destructor calls, to generate a situation that there's only 'invoke @setjmp'
+; and no other longjmpable calls.
+define i32 @setjmp_only() personality i8* bitcast (i32 (...)* @__gxx_wasm_personality_v0 to i8*) {
+; CHECK-LABEL: @setjmp_only
+entry:
+  %buf = alloca [1 x %struct.__jmp_buf_tag], align 16
+  %arraydecay = getelementptr inbounds [1 x %struct.__jmp_buf_tag], [1 x %struct.__jmp_buf_tag]* %buf, i32 0, i32 0
+  %call = invoke i32 @setjmp(%struct.__jmp_buf_tag* noundef %arraydecay) #0
+          to label %invoke.cont unwind label %ehcleanup
+
+invoke.cont:                                      ; preds = %entry
+  ret i32 %call
+; CHECK: invoke.cont:
+; The remaining setjmp call is converted to constant 0, because setjmp returns 0
+; when called directly.
+; CHECK:   ret i32 0
+
+ehcleanup:                                        ; preds = %entry
+  %0 = cleanuppad within none []
+  cleanupret from %0 unwind to caller
+}
+
 declare void @foo()
 ; Function Attrs: nounwind
 declare %struct.Temp* @_ZN4TempD2Ev(%struct.Temp* %this) #2