[WebAssemblyLowerEmscriptenEHSjLj] Avoid lifetime of phi (#150932)

nikic · web-flow · commit fc90685354ca · 2025-07-29T09:58:57.000+02:00
After #149310 lifetime intrinsics require an alloca argument, an invariant that this pass can break. I've fixed this in two ways: * First, move static allocas into the entry block. Currently, the way the pass splits the entry block makes all allocas dynamic, which I assume was not actually intended. This will avoid unnecessary SSA reconstruction for allocas as well, and thus avoid the problem. * If this fails (for dynamic allocas) drop all lifetime intrinsics if any one of them would require a rewrite during SSA reconstruction. Fixes #150498.
diff --git a/llvm/lib/Target/WebAssembly/WebAssemblyLowerEmscriptenEHSjLj.cpp b/llvm/lib/Target/WebAssembly/WebAssemblyLowerEmscriptenEHSjLj.cpp
@@ -782,6 +782,24 @@ void WebAssemblyLowerEmscriptenEHSjLj::rebuildSSA(Function &F) {
     for (Instruction &I : BB) {
       if (I.getType()->isVoidTy())
         continue;
+
+      if (isa<AllocaInst>(&I)) {
+        // If the alloca has any lifetime marker that is no longer dominated
+        // by the alloca, remove all lifetime markers. Lifetime markers must
+        // always work directly on the alloca, and this is no longer possible.
+        bool HasNonDominatedLifetimeMarker = any_of(I.users(), [&](User *U) {
+          auto *UserI = cast<Instruction>(U);
+          return UserI->isLifetimeStartOrEnd() && !DT.dominates(&I, UserI);
+        });
+        if (HasNonDominatedLifetimeMarker) {
+          for (User *U : make_early_inc_range(I.users())) {
+            auto *UserI = cast<Instruction>(U);
+            if (UserI->isLifetimeStartOrEnd())
+              UserI->eraseFromParent();
+          }
+        }
+      }
+
       unsigned VarID = SSA.AddVariable(I.getName(), I.getType());
       // If a value is defined by an invoke instruction, it is only available in
       // its normal destination and not in its unwind destination.
@@ -1269,10 +1287,20 @@ bool WebAssemblyLowerEmscriptenEHSjLj::runSjLjOnFunction(Function &F) {
 
   // Setjmp preparation
 
+  SmallVector<AllocaInst *> StaticAllocas;
+  for (Instruction &I : F.getEntryBlock())
+    if (auto *AI = dyn_cast<AllocaInst>(&I))
+      if (AI->isStaticAlloca())
+        StaticAllocas.push_back(AI);
+
   BasicBlock *Entry = &F.getEntryBlock();
   DebugLoc FirstDL = getOrCreateDebugLoc(&*Entry->begin(), F.getSubprogram());
   SplitBlock(Entry, &*Entry->getFirstInsertionPt());
 
+  // Move static allocas back into the entry block, so they stay static.
+  for (AllocaInst *AI : StaticAllocas)
+    AI->moveBefore(Entry->getTerminator()->getIterator());
+
   IRB.SetInsertPoint(Entry->getTerminator()->getIterator());
   // This alloca'ed pointer is used by the runtime to identify function
   // invocations. It's just for pointer comparisons. It will never be
diff --git a/llvm/test/CodeGen/WebAssembly/lower-em-sjlj-alloca.ll b/llvm/test/CodeGen/WebAssembly/lower-em-sjlj-alloca.ll
@@ -0,0 +1,129 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --version 5
+; RUN: opt -S -wasm-lower-em-ehsjlj -wasm-enable-sjlj -mtriple=wasm32-unknown-emscripten < %s | FileCheck %s
+
+@buf = external global i8
+declare i32 @setjmp(ptr) returns_twice
+declare void @dummy()
+
+define void @test_static() {
+; CHECK-LABEL: define void @test_static() personality ptr @__gxx_wasm_personality_v0 {
+; CHECK-NEXT:  [[ENTRY:.*]]:
+; CHECK-NEXT:    [[X:%.*]] = alloca i32, align 4
+; CHECK-NEXT:    [[FUNCTIONINVOCATIONID:%.*]] = alloca i32, align 4
+; CHECK-NEXT:    br label %[[SETJMP_DISPATCH:.*]]
+; CHECK:       [[SETJMP_DISPATCH]]:
+; CHECK-NEXT:    [[VAL1:%.*]] = phi i32 [ [[VAL:%.*]], %[[IF_END:.*]] ], [ undef, %[[ENTRY]] ]
+; CHECK-NEXT:    [[LABEL_PHI:%.*]] = phi i32 [ [[LABEL:%.*]], %[[IF_END]] ], [ -1, %[[ENTRY]] ]
+; CHECK-NEXT:    switch i32 [[LABEL_PHI]], label %[[ENTRY_SPLIT:.*]] [
+; CHECK-NEXT:      i32 1, label %[[ENTRY_SPLIT_SPLIT:.*]]
+; CHECK-NEXT:    ]
+; CHECK:       [[ENTRY_SPLIT]]:
+; CHECK-NEXT:    call void @llvm.lifetime.start.p0(i64 4, ptr [[X]])
+; CHECK-NEXT:    call void @__wasm_setjmp(ptr @buf, i32 1, ptr [[FUNCTIONINVOCATIONID]])
+; CHECK-NEXT:    br label %[[ENTRY_SPLIT_SPLIT]]
+; CHECK:       [[ENTRY_SPLIT_SPLIT]]:
+; CHECK-NEXT:    [[SETJMP_RET:%.*]] = phi i32 [ 0, %[[ENTRY_SPLIT]] ], [ [[VAL1]], %[[SETJMP_DISPATCH]] ]
+; CHECK-NEXT:    [[CMP:%.*]] = icmp eq i32 [[SETJMP_RET]], 0
+; CHECK-NEXT:    br i1 [[CMP]], label %[[IF:.*]], label %[[ELSE:.*]]
+; CHECK:       [[IF]]:
+; CHECK-NEXT:    invoke void @dummy()
+; CHECK-NEXT:            to [[DOTNOEXC:label %.*]] unwind label %[[CATCH_DISPATCH_LONGJMP:.*]]
+; CHECK:       [[_NOEXC:.*:]]
+; CHECK-NEXT:    ret void
+; CHECK:       [[ELSE]]:
+; CHECK-NEXT:    call void @llvm.lifetime.end.p0(i64 4, ptr [[X]])
+; CHECK-NEXT:    ret void
+; CHECK:       [[CATCH_DISPATCH_LONGJMP]]:
+; CHECK-NEXT:    [[TMP0:%.*]] = catchswitch within none [label %catch.longjmp] unwind to caller
+; CHECK:       [[CATCH_LONGJMP:.*:]]
+; CHECK-NEXT:    [[TMP1:%.*]] = catchpad within [[TMP0]] []
+; CHECK-NEXT:    [[THROWN:%.*]] = call ptr @llvm.wasm.catch(i32 1)
+; CHECK-NEXT:    [[ENV_GEP:%.*]] = getelementptr { ptr, i32 }, ptr [[THROWN]], i32 0, i32 0
+; CHECK-NEXT:    [[VAL_GEP:%.*]] = getelementptr { ptr, i32 }, ptr [[THROWN]], i32 0, i32 1
+; CHECK-NEXT:    [[ENV:%.*]] = load ptr, ptr [[ENV_GEP]], align 4
+; CHECK-NEXT:    [[VAL]] = load i32, ptr [[VAL_GEP]], align 4
+; CHECK-NEXT:    [[LABEL]] = call i32 @__wasm_setjmp_test(ptr [[ENV]], ptr [[FUNCTIONINVOCATIONID]]) [ "funclet"(token [[TMP1]]) ]
+; CHECK-NEXT:    [[TMP2:%.*]] = icmp eq i32 [[LABEL]], 0
+; CHECK-NEXT:    br i1 [[TMP2]], label %[[IF_THEN:.*]], label %[[IF_END]]
+; CHECK:       [[IF_THEN]]:
+; CHECK-NEXT:    call void @__wasm_longjmp(ptr [[ENV]], i32 [[VAL]]) [ "funclet"(token [[TMP1]]) ]
+; CHECK-NEXT:    unreachable
+; CHECK:       [[IF_END]]:
+; CHECK-NEXT:    catchret from [[TMP1]] to label %[[SETJMP_DISPATCH]]
+;
+entry:
+  %x = alloca i32, align 4
+  call void @llvm.lifetime.start.p0(i64 4, ptr %x)
+  %call = call i32 @setjmp(ptr @buf) returns_twice
+  %cmp = icmp eq i32 %call, 0
+  br i1 %cmp, label %if, label %else
+
+if:
+  call void @dummy()
+  ret void
+
+else:
+  call void @llvm.lifetime.end.p0(i64 4, ptr %x)
+  ret void
+}
+
+define void @test_dynamic(i32 %size) {
+; CHECK-LABEL: define void @test_dynamic(
+; CHECK-SAME: i32 [[SIZE:%.*]]) personality ptr @__gxx_wasm_personality_v0 {
+; CHECK-NEXT:  [[ENTRY:.*]]:
+; CHECK-NEXT:    [[FUNCTIONINVOCATIONID:%.*]] = alloca i32, align 4
+; CHECK-NEXT:    br label %[[SETJMP_DISPATCH:.*]]
+; CHECK:       [[SETJMP_DISPATCH]]:
+; CHECK-NEXT:    [[VAL1:%.*]] = phi i32 [ [[VAL:%.*]], %[[IF_END:.*]] ], [ undef, %[[ENTRY]] ]
+; CHECK-NEXT:    [[LABEL_PHI:%.*]] = phi i32 [ [[LABEL:%.*]], %[[IF_END]] ], [ -1, %[[ENTRY]] ]
+; CHECK-NEXT:    switch i32 [[LABEL_PHI]], label %[[ENTRY_SPLIT:.*]] [
+; CHECK-NEXT:      i32 1, label %[[ENTRY_SPLIT_SPLIT:.*]]
+; CHECK-NEXT:    ]
+; CHECK:       [[ENTRY_SPLIT]]:
+; CHECK-NEXT:    [[X:%.*]] = alloca i32, i32 [[SIZE]], align 4
+; CHECK-NEXT:    call void @__wasm_setjmp(ptr @buf, i32 1, ptr [[FUNCTIONINVOCATIONID]])
+; CHECK-NEXT:    br label %[[ENTRY_SPLIT_SPLIT]]
+; CHECK:       [[ENTRY_SPLIT_SPLIT]]:
+; CHECK-NEXT:    [[SETJMP_RET:%.*]] = phi i32 [ 0, %[[ENTRY_SPLIT]] ], [ [[VAL1]], %[[SETJMP_DISPATCH]] ]
+; CHECK-NEXT:    [[CMP:%.*]] = icmp eq i32 [[SETJMP_RET]], 0
+; CHECK-NEXT:    br i1 [[CMP]], label %[[IF:.*]], label %[[ELSE:.*]]
+; CHECK:       [[IF]]:
+; CHECK-NEXT:    invoke void @dummy()
+; CHECK-NEXT:            to [[DOTNOEXC:label %.*]] unwind label %[[CATCH_DISPATCH_LONGJMP:.*]]
+; CHECK:       [[_NOEXC:.*:]]
+; CHECK-NEXT:    ret void
+; CHECK:       [[ELSE]]:
+; CHECK-NEXT:    ret void
+; CHECK:       [[CATCH_DISPATCH_LONGJMP]]:
+; CHECK-NEXT:    [[TMP0:%.*]] = catchswitch within none [label %catch.longjmp] unwind to caller
+; CHECK:       [[CATCH_LONGJMP:.*:]]
+; CHECK-NEXT:    [[TMP1:%.*]] = catchpad within [[TMP0]] []
+; CHECK-NEXT:    [[THROWN:%.*]] = call ptr @llvm.wasm.catch(i32 1)
+; CHECK-NEXT:    [[ENV_GEP:%.*]] = getelementptr { ptr, i32 }, ptr [[THROWN]], i32 0, i32 0
+; CHECK-NEXT:    [[VAL_GEP:%.*]] = getelementptr { ptr, i32 }, ptr [[THROWN]], i32 0, i32 1
+; CHECK-NEXT:    [[ENV:%.*]] = load ptr, ptr [[ENV_GEP]], align 4
+; CHECK-NEXT:    [[VAL]] = load i32, ptr [[VAL_GEP]], align 4
+; CHECK-NEXT:    [[LABEL]] = call i32 @__wasm_setjmp_test(ptr [[ENV]], ptr [[FUNCTIONINVOCATIONID]]) [ "funclet"(token [[TMP1]]) ]
+; CHECK-NEXT:    [[TMP2:%.*]] = icmp eq i32 [[LABEL]], 0
+; CHECK-NEXT:    br i1 [[TMP2]], label %[[IF_THEN:.*]], label %[[IF_END]]
+; CHECK:       [[IF_THEN]]:
+; CHECK-NEXT:    call void @__wasm_longjmp(ptr [[ENV]], i32 [[VAL]]) [ "funclet"(token [[TMP1]]) ]
+; CHECK-NEXT:    unreachable
+; CHECK:       [[IF_END]]:
+; CHECK-NEXT:    catchret from [[TMP1]] to label %[[SETJMP_DISPATCH]]
+;
+entry:
+  %x = alloca i32, i32 %size, align 4
+  call void @llvm.lifetime.start.p0(i64 -1, ptr %x)
+  %call = call i32 @setjmp(ptr @buf) returns_twice
+  %cmp = icmp eq i32 %call, 0
+  br i1 %cmp, label %if, label %else
+
+if:
+  call void @dummy()
+  ret void
+
+else:
+  call void @llvm.lifetime.end.p0(i64 -1, ptr %x)
+  ret void
+}
diff --git a/llvm/test/CodeGen/WebAssembly/lower-em-sjlj-debuginfo.ll b/llvm/test/CodeGen/WebAssembly/lower-em-sjlj-debuginfo.ll
@@ -16,10 +16,10 @@ entry:
   call void @foo(), !dbg !7
   ret void, !dbg !8
 ; CHECK: entry:
-  ; CHECK-NEXT: %functionInvocationId = alloca i32, align 4, !dbg ![[DL0:.*]]
+  ; CHECK-NEXT: %buf = alloca [1 x %struct.__jmp_buf_tag], align 16, !dbg ![[DL0:.*]]
+  ; CHECK-NEXT: %functionInvocationId = alloca i32, align 4, !dbg ![[DL0]]
 
 ; CHECK: entry.split:
-  ; CHECK: alloca {{.*}}, !dbg ![[DL0]]
   ; CHECK: call void @__wasm_setjmp{{.*}}, !dbg ![[DL1:.*]]
   ; CHECK-NEXT: br {{.*}}, !dbg ![[DL2:.*]]
 
diff --git a/llvm/test/CodeGen/WebAssembly/lower-em-sjlj.ll b/llvm/test/CodeGen/WebAssembly/lower-em-sjlj.ll
@@ -22,17 +22,17 @@ entry:
   call void @longjmp(ptr %buf, i32 1) #1
   unreachable
 ; CHECK: entry:
+; CHECK-NEXT:  %buf = alloca [1 x %struct.__jmp_buf_tag], align 16
 ; CHECK-NEXT: %functionInvocationId = alloca i32, align 4
 ; CHECK-NEXT: br label %entry.split
 
 ; CHECK: entry.split
-; CHECK-NEXT: %[[BUF:.*]] = alloca [1 x %struct.__jmp_buf_tag]
-; CHECK-NEXT: call void @__wasm_setjmp(ptr %[[BUF]], i32 1, ptr %functionInvocationId)
+; CHECK-NEXT: call void @__wasm_setjmp(ptr %buf, i32 1, ptr %functionInvocationId)
 ; CHECK-NEXT: br label %entry.split.split
 
 ; CHECK: entry.split.split:
 ; CHECK-NEXT: phi i32 [ 0, %entry.split ], [ %[[LONGJMP_RESULT:.*]], %if.end ]
-; CHECK-NEXT: %[[JMPBUF:.*]] = ptrtoint ptr %[[BUF]] to [[PTR]]
+; CHECK-NEXT: %[[JMPBUF:.*]] = ptrtoint ptr %buf to [[PTR]]
 ; CHECK-NEXT: store [[PTR]] 0, ptr @__THREW__
 ; CHECK-NEXT: call cc{{.*}} void @__invoke_void_[[PTR]]_i32(ptr @emscripten_longjmp, [[PTR]] %[[JMPBUF]], i32 1)
 ; CHECK-NEXT: %[[__THREW__VAL:.*]] = load [[PTR]], ptr @__THREW__
diff --git a/llvm/test/CodeGen/WebAssembly/lower-wasm-ehsjlj.ll b/llvm/test/CodeGen/WebAssembly/lower-wasm-ehsjlj.ll
@@ -108,7 +108,7 @@ catch:                                            ; preds = %catch.start
   call void @__cxa_end_catch() [ "funclet"(token %2) ]
   catchret from %2 to label %catchret.dest
 ; CHECK: catch:                                            ; preds = %catch.start
-; CHECK-NEXT:   %exn = load ptr, ptr %exn.slot6, align 4
+; CHECK-NEXT:   %exn = load ptr, ptr %exn.slot, align 4
 ; CHECK-NEXT:   %5 = call ptr @__cxa_begin_catch(ptr %exn) #3 [ "funclet"(token %2) ]
 ; CHECK-NEXT:   invoke void @__cxa_end_catch() [ "funclet"(token %2) ]
 ; CHECK-NEXT:           to label %.noexc unwind label %catch.dispatch.longjmp
diff --git a/llvm/test/CodeGen/WebAssembly/lower-wasm-sjlj.ll b/llvm/test/CodeGen/WebAssembly/lower-wasm-sjlj.ll
@@ -25,26 +25,24 @@ entry:
   unreachable
 
 ; CHECK:    entry:
+; CHECK-NEXT: %buf = alloca [1 x %struct.__jmp_buf_tag], align 16
 ; CHECK-NEXT: %functionInvocationId = alloca i32, align 4
 ; CHECK-NEXT: br label %setjmp.dispatch
 
 ; CHECK:    setjmp.dispatch:
 ; CHECK-NEXT: %[[VAL2:.*]] = phi i32 [ %val, %if.end ], [ undef, %entry ]
-; CHECK-NEXT: %[[BUF:.*]] = phi ptr [ %[[BUF2:.*]], %if.end ], [ undef, %entry ]
 ; CHECK-NEXT: %label.phi = phi i32 [ %label, %if.end ], [ -1, %entry ]
 ; CHECK-NEXT: switch i32 %label.phi, label %entry.split [
 ; CHECK-NEXT:   i32 1, label %entry.split.split
 ; CHECK-NEXT: ]
 
 ; CHECK:    entry.split:
-; CHECK-NEXT: %buf = alloca [1 x %struct.__jmp_buf_tag], align 16
 ; CHECK-NEXT: call void @__wasm_setjmp(ptr %buf, i32 1, ptr %functionInvocationId)
 ; CHECK-NEXT: br label %entry.split.split
 
 ; CHECK:    entry.split.split:
-; CHECK-NEXT: %[[BUF2]] = phi ptr [ %[[BUF]], %setjmp.dispatch ], [ %buf, %entry.split ]
 ; CHECK-NEXT: %setjmp.ret = phi i32 [ 0, %entry.split ], [ %[[VAL2]], %setjmp.dispatch ]
-; CHECK-NEXT: invoke void @__wasm_longjmp(ptr %[[BUF2]], i32 1)
+; CHECK-NEXT: invoke void @__wasm_longjmp(ptr %buf, i32 1)
 ; CHECK-NEXT:         to label %.noexc unwind label %catch.dispatch.longjmp
 
 ; CHECK:    .noexc:
