[PATCH] D131387: [WebAssembly] Produce error when encountering unlowerable Wasm global accesses

[Alex Bradbury via Phabricator via llvm-commits]

asb created this revision.
asb added reviewers: pmatos, aheejin, tlively, sbc100.
Herald added subscribers: wingo, StephenFan, ecnelises, sameer.abuasal, sunfish, hiraditya, jgravelle-google, dschuff.
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asb requested review of this revision.
Herald added a project: LLVM.

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.


https://reviews.llvm.org/D131387

Files:
  llvm/lib/Target/WebAssembly/WebAssemblyISelLowering.cpp
  llvm/test/CodeGen/WebAssembly/global-get-unlowerable.ll
  llvm/test/CodeGen/WebAssembly/global-set-unlowerable.ll


Index: llvm/test/CodeGen/WebAssembly/global-set-unlowerable.ll
===================================================================
--- /dev/null
+++ llvm/test/CodeGen/WebAssembly/global-set-unlowerable.ll
@@ -0,0 +1,24 @@
+; 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) {
+entry:
+  br i1 %bool, label %if.end.i, label %if.then.i
+
+if.then.i:
+  br label %if.end.i
+
+if.end.i:
+  %sel = phi ptr addrspace(1) [ @g1, %entry ], [ @g2, %if.then.i ]
+  store i32 100, ptr addrspace(1) %sel
+  ret void
+}
Index: llvm/test/CodeGen/WebAssembly/global-get-unlowerable.ll
===================================================================
--- /dev/null
+++ llvm/test/CodeGen/WebAssembly/global-get-unlowerable.ll
@@ -0,0 +1,24 @@
+; 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) {
+entry:
+  br i1 %bool, label %if.end.i, label %if.then.i
+
+if.then.i:
+  br label %if.end.i
+
+if.end.i:
+  %sel = phi ptr addrspace(1) [ @g1, %entry ], [ @g2, %if.then.i ]
+  %gval = load i32, ptr addrspace(1) %sel
+  ret i32 %gval
+}
Index: llvm/lib/Target/WebAssembly/WebAssemblyISelLowering.cpp
===================================================================
--- llvm/lib/Target/WebAssembly/WebAssemblyISelLowering.cpp
+++ llvm/lib/Target/WebAssembly/WebAssemblyISelLowering.cpp
@@ -1581,6 +1581,11 @@
     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 @@
     return Result;
   }
 
+  if (WebAssembly::isWasmVarAddressSpace(LN->getAddressSpace()))
+    report_fatal_error(
+        "Encountered an unlowerable load from the wasm_var address space",
+        false);
+
   return Op;
 }
 


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