[llvm] 104a24e - [WebAssembly] Produce error when encountering unlowerable Wasm global accesses

[Alex Bradbury via llvm-commits]

Author: Alex Bradbury
Date: 2022-08-10T10:34:10+01:00
New Revision: 104a24ec8bd4bc0e0acbb81c03b916c0c64e85b2

URL: https://github.com/llvm/llvm-project/commit/104a24ec8bd4bc0e0acbb81c03b916c0c64e85b2
DIFF: https://github.com/llvm/llvm-project/commit/104a24ec8bd4bc0e0acbb81c03b916c0c64e85b2.diff

LOG: [WebAssembly] Produce error when encountering unlowerable Wasm global accesses

WebAssembly globals are represented as IR globals with the wasm_var
address space (AS1). Prior to this patch, a wasm global load that isn't
lowerable will produce a failure to select, while a wasm global store
will produced incorrect code. This patch ensures we consistently produce
a clear error.

As noted in the test cases, it's conceivable that a frontend or an
optimisation pass could produce similar IR even in the presence of the
semantic restrictions on pointers to Wasm globals in the frontend, which
is a separate problem to address.

Differential Revision: https://reviews.llvm.org/D131387

Added: 
    llvm/test/CodeGen/WebAssembly/global-get-unlowerable.ll
    llvm/test/CodeGen/WebAssembly/global-set-unlowerable.ll

Modified: 
    llvm/lib/Target/WebAssembly/WebAssemblyISelLowering.cpp

Removed: 
    


################################################################################
diff  --git a/llvm/lib/Target/WebAssembly/WebAssemblyISelLowering.cpp b/llvm/lib/Target/WebAssembly/WebAssemblyISelLowering.cpp
index ab6d6b4f7ef1..84823218216b 100644
--- a/llvm/lib/Target/WebAssembly/WebAssemblyISelLowering.cpp
+++ b/llvm/lib/Target/WebAssembly/WebAssemblyISelLowering.cpp
@@ -1581,6 +1581,11 @@ SDValue WebAssemblyTargetLowering::LowerStore(SDValue Op,
     return DAG.getNode(WebAssemblyISD::LOCAL_SET, DL, Tys, Ops);
   }
 
+  if (WebAssembly::isWasmVarAddressSpace(SN->getAddressSpace()))
+    report_fatal_error(
+        "Encountered an unlowerable store to the wasm_var address space",
+        false);
+
   return Op;
 }
 
@@ -1636,6 +1641,11 @@ SDValue WebAssemblyTargetLowering::LowerLoad(SDValue Op,
     return Result;
   }
 
+  if (WebAssembly::isWasmVarAddressSpace(LN->getAddressSpace()))
+    report_fatal_error(
+        "Encountered an unlowerable load from the wasm_var address space",
+        false);
+
   return Op;
 }
 

diff  --git a/llvm/test/CodeGen/WebAssembly/global-get-unlowerable.ll b/llvm/test/CodeGen/WebAssembly/global-get-unlowerable.ll
new file mode 100644
index 000000000000..093340880b87
--- /dev/null
+++ b/llvm/test/CodeGen/WebAssembly/global-get-unlowerable.ll
@@ -0,0 +1,17 @@
+; RUN: not llc < %s --mtriple=wasm32 2>&1 | FileCheck %s
+
+; Demonstrates a code pattern that could be encountered even with frontend
+; restrictions on creating new pointers to globals. In the absence of a better
+; fix, the backend should produce a comprehensible message for why it can't
+; continue.
+
+; CHECK: LVM ERROR: Encountered an unlowerable load from the wasm_var address space
+
+ at g1 = external addrspace(1) global i32
+ at g2 = external addrspace(1) global i32
+
+define i32 @global_get_phi(i1 zeroext %bool) {
+  %sel = select i1 %bool, ptr addrspace(1) @g1, ptr addrspace(1) @g2
+  %gval = load i32, ptr addrspace(1) %sel
+  ret i32 %gval
+}

diff  --git a/llvm/test/CodeGen/WebAssembly/global-set-unlowerable.ll b/llvm/test/CodeGen/WebAssembly/global-set-unlowerable.ll
new file mode 100644
index 000000000000..9600fe638249
--- /dev/null
+++ b/llvm/test/CodeGen/WebAssembly/global-set-unlowerable.ll
@@ -0,0 +1,17 @@
+; RUN: not llc < %s --mtriple=wasm32 2>&1 | FileCheck %s
+
+; Demonstrates a code pattern that could be encountered even with frontend
+; restrictions on creating new pointers to globals. In the absence of a better
+; fix, the backend should produce a comprehensible message for why it can't
+; continue.
+
+; CHECK: LVM ERROR: Encountered an unlowerable store to the wasm_var address space
+
+ at g1 = external addrspace(1) global i32
+ at g2 = external addrspace(1) global i32
+
+define void @global_set_phi(i1 zeroext %bool) {
+  %sel = select i1 %bool, ptr addrspace(1) @g1, ptr addrspace(1) @g2
+  store i32 100, ptr addrspace(1) %sel
+  ret void
+}