[llvm] [WebAssembly] Remove threwValue comparison after __wasm_setjmp_test (PR #86633)

[Heejin Ahn via llvm-commits]

https://github.com/aheejin updated https://github.com/llvm/llvm-project/pull/86633

>From a5201f175d8c9abbe90054f2075e6cc0169d4d92 Mon Sep 17 00:00:00 2001
From: Heejin Ahn <aheejin at gmail.com>
Date: Mon, 18 Mar 2024 09:24:15 +0000
Subject: [PATCH] [WebAssembly] Remove threwValue comparison after
 __wasm_setjmp_test

Currently the code thinks a `longjmp` occurred if both `__THREW__` and
`__threwValue` are nonzero. But `__threwValue` can be 0, and the
`longjmp` library function should change it to 1 in case it is 0:
https://en.cppreference.com/w/c/program/longjmp

Emscripten libraries were not consistent about that, but after
https://github.com/emscripten-core/emscripten/pull/21493 and
https://github.com/emscripten-core/emscripten/pull/21502, we correctly
pass 1 in case the input is 0. So there will be no case `__threwValue`
is 0. And regardless of what `longjmp` library function does, treating
`longjmp`'s 0 input to its second argument as "not longjmping" doesn't
seem right.

I'm not sure where that `__threwValue` checking came from, but probably
I was porting then fastcomp's implementation and moved this part just
verbatim:
https://github.com/emscripten-core/emscripten-fastcomp/blob/9bdc7bb4fc595fe05a021b06fe350e8494a741a1/lib/Target/JSBackend/CallHandlers.h#L274-L278

Just for the context, how this was discovered:
https://github.com/emscripten-core/emscripten/pull/21502#pullrequestreview-1942160300
---
 .../WebAssembly/WebAssemblyLowerEmscriptenEHSjLj.cpp      | 8 +++-----
 llvm/test/CodeGen/WebAssembly/lower-em-ehsjlj.ll          | 7 +++----
 llvm/test/CodeGen/WebAssembly/lower-em-sjlj.ll            | 4 +---
 3 files changed, 7 insertions(+), 12 deletions(-)

diff --git a/llvm/lib/Target/WebAssembly/WebAssemblyLowerEmscriptenEHSjLj.cpp b/llvm/lib/Target/WebAssembly/WebAssemblyLowerEmscriptenEHSjLj.cpp
index 027ee1086bf4e0..0788d0c3a72136 100644
--- a/llvm/lib/Target/WebAssembly/WebAssemblyLowerEmscriptenEHSjLj.cpp
+++ b/llvm/lib/Target/WebAssembly/WebAssemblyLowerEmscriptenEHSjLj.cpp
@@ -153,7 +153,7 @@
 ///      %__THREW__.val = __THREW__;
 ///      __THREW__ = 0;
 ///      %__threwValue.val = __threwValue;
-///      if (%__THREW__.val != 0 & %__threwValue.val != 0) {
+///      if (%__THREW__.val != 0) {
 ///        %label = __wasm_setjmp_test(%__THREW__.val, functionInvocationId);
 ///        if (%label == 0)
 ///          emscripten_longjmp(%__THREW__.val, %__threwValue.val);
@@ -712,12 +712,10 @@ void WebAssemblyLowerEmscriptenEHSjLj::wrapTestSetjmp(
   BasicBlock *ThenBB1 = BasicBlock::Create(C, "if.then1", F);
   BasicBlock *ElseBB1 = BasicBlock::Create(C, "if.else1", F);
   BasicBlock *EndBB1 = BasicBlock::Create(C, "if.end", F);
-  Value *ThrewCmp = IRB.CreateICmpNE(Threw, getAddrSizeInt(M, 0));
   Value *ThrewValue = IRB.CreateLoad(IRB.getInt32Ty(), ThrewValueGV,
                                      ThrewValueGV->getName() + ".val");
-  Value *ThrewValueCmp = IRB.CreateICmpNE(ThrewValue, IRB.getInt32(0));
-  Value *Cmp1 = IRB.CreateAnd(ThrewCmp, ThrewValueCmp, "cmp1");
-  IRB.CreateCondBr(Cmp1, ThenBB1, ElseBB1);
+  Value *ThrewCmp = IRB.CreateICmpNE(Threw, getAddrSizeInt(M, 0));
+  IRB.CreateCondBr(ThrewCmp, ThenBB1, ElseBB1);
 
   // Generate call.em.longjmp BB once and share it within the function
   if (!CallEmLongjmpBB) {
diff --git a/llvm/test/CodeGen/WebAssembly/lower-em-ehsjlj.ll b/llvm/test/CodeGen/WebAssembly/lower-em-ehsjlj.ll
index 32942cd92e684f..d88f42a4dc5847 100644
--- a/llvm/test/CodeGen/WebAssembly/lower-em-ehsjlj.ll
+++ b/llvm/test/CodeGen/WebAssembly/lower-em-ehsjlj.ll
@@ -22,10 +22,8 @@ entry:
           to label %try.cont unwind label %lpad
 
 ; CHECK:    entry.split.split:
-; CHECK:      %[[CMP0:.*]] = icmp ne i32 %__THREW__.val, 0
-; CHECK-NEXT: %__threwValue.val = load i32, ptr @__threwValue
-; CHECK-NEXT: %[[CMP1:.*]] = icmp ne i32 %__threwValue.val, 0
-; CHECK-NEXT: %[[CMP:.*]] = and i1 %[[CMP0]], %[[CMP1]]
+; CHECK:      %__threwValue.val = load i32, ptr @__threwValue
+; CHECK-NEXT: %[[CMP:.*]] = icmp ne i32 %__THREW__.val, 0
 ; CHECK-NEXT: br i1 %[[CMP]], label %if.then1, label %if.else1
 
 ; This is exception checking part. %if.else1 leads here
@@ -121,6 +119,7 @@ if.end:                                           ; preds = %entry
 ; CHECK-NEXT: unreachable
 
 ; CHECK:    normal:
+; CHECK-NEXT: %__threwValue.val = load i32, ptr @__threwValue, align 4
 ; CHECK-NEXT: icmp ne i32 %__THREW__.val, 0
 
 return:                                           ; preds = %if.end, %entry
diff --git a/llvm/test/CodeGen/WebAssembly/lower-em-sjlj.ll b/llvm/test/CodeGen/WebAssembly/lower-em-sjlj.ll
index 27ec95a2c462ab..dca4c59d7c8740 100644
--- a/llvm/test/CodeGen/WebAssembly/lower-em-sjlj.ll
+++ b/llvm/test/CodeGen/WebAssembly/lower-em-sjlj.ll
@@ -37,10 +37,8 @@ entry:
 ; CHECK-NEXT: call cc{{.*}} void @__invoke_void_[[PTR]]_i32(ptr @emscripten_longjmp, [[PTR]] %[[JMPBUF]], i32 1)
 ; CHECK-NEXT: %[[__THREW__VAL:.*]] = load [[PTR]], ptr @__THREW__
 ; CHECK-NEXT: store [[PTR]] 0, ptr @__THREW__
-; CHECK-NEXT: %[[CMP0:.*]] = icmp ne [[PTR]] %__THREW__.val, 0
 ; CHECK-NEXT: %[[THREWVALUE_VAL:.*]] = load i32, ptr @__threwValue
-; CHECK-NEXT: %[[CMP1:.*]] = icmp ne i32 %[[THREWVALUE_VAL]], 0
-; CHECK-NEXT: %[[CMP:.*]] = and i1 %[[CMP0]], %[[CMP1]]
+; CHECK-NEXT: %[[CMP:.*]] = icmp ne [[PTR]] %__THREW__.val, 0
 ; CHECK-NEXT: br i1 %[[CMP]], label %if.then1, label %if.else1
 
 ; CHECK: entry.split.split.split: