wasm-emscripten-finalize: Handle relocatable code in AsmConstWalker (#2035)

When replacing the first argument to an asm call, allow more complex
expressions for expressing the address.

This fixes the case where the first argument might be the result
of adding a constant to __memory_base.

Author: sbc100

CHANGELOG.md

@@ -15,6 +15,11 @@ full changeset diff at the end of each section.
 Current Trunk
 -------------
 
+v81
+---
+
+- Fix AsmConstWalker handling of string address in arg0 with -fPIC code
+
 v80
 ---
 

src/wasm/wasm-emscripten.cpp

@@ -525,30 +525,37 @@ void AsmConstWalker::visitCall(Call* curr) {
     auto baseSig = getSig(curr);
     auto sig = fixupNameWithSig(curr->target, baseSig);
     auto* arg = curr->operands[0];
-    if (auto* get = arg->dynCast<GetLocal>()) {
-      // The argument may be a local.get, in which case, the last set in this
-      // basic block has the value.
-      auto* set = sets[get->index];
-      if (set) {
-        assert(set->index == get->index);
-        arg = set->value;
-      }
-    } else if (auto* value = arg->dynCast<Binary>()) {
-      // In the dynamic linking case the address of the string constant
-      // is the result of adding its offset to __memory_base.
-      // In this case are only looking for the offset with the data segment so
-      // the RHS of the addition is just what we want.
-      assert(value->op == AddInt32);
-      arg = value->right;
-    }
-
-    auto* value = arg->dynCast<Const>();
-    if (!value)
-      Fatal() << "Unexpected arg0 type (" << getExpressionName(arg)
+    while (!arg->dynCast<Const>()) {
+      if (auto* get = arg->dynCast<GetLocal>()) {
+        // The argument may be a local.get, in which case, the last set in this
+        // basic block has the value.
+        auto* set = sets[get->index];
+        if (set) {
+          assert(set->index == get->index);
+          arg = set->value;
+        }
+      } else if (auto* value = arg->dynCast<Binary>()) {
+        // In the dynamic linking case the address of the string constant
+        // is the result of adding its offset to __memory_base.
+        // In this case are only looking for the offset with the data segment so
+        // the RHS of the addition is just what we want.
+        assert(value->op == AddInt32);
+        arg = value->right;
+      } else {
+        if (!value) {
+          Fatal() << "Unexpected arg0 type (" << getExpressionName(arg)
               << ") in call to to: " << import->base;
+        }
+      }
+    }
+
+    auto* value = arg->cast<Const>();
     auto code = codeForConstAddr(wasm, segmentOffsets, value);
-    value->value = idLiteralForCode(code);
     sigsForCode[code].insert(sig);
+
+    // Replace the first argument to the call with a Const index
+    Builder builder(wasm);
+    curr->operands[0] = builder.makeConst(idLiteralForCode(code));
   }
 }
 

test/lld/em_asm_O0.wast.out

@@ -34,16 +34,16 @@
    )
   )
   (local.set $t1
-   (i32.const 2)
+   (i32.const 621)
   )
   (local.set $t2
-   (i32.const 1)
+   (i32.const 601)
   )
   (drop
    (call $emscripten_asm_const_ii
-    (local.get $t1)
+    (i32.const 2)
     (call $emscripten_asm_const_iii
-     (local.get $t2)
+     (i32.const 1)
      (i32.const 13)
      (i32.const 27)
     )

test/lld/em_asm_shared.wast.out

@@ -48,12 +48,7 @@
   )
   (drop
    (call $emscripten_asm_const_iii
-    (i32.add
-     (local.tee $1
-      (global.get $gimport$3)
-     )
-     (i32.const 0)
-    )
+    (i32.const 0)
     (i32.add
      (local.get $0)
      (i32.const 24)
@@ -80,10 +75,7 @@
    )
    (local.tee $2
     (call $emscripten_asm_const_iii
-     (i32.add
-      (local.get $1)
-      (i32.const 1)
-     )
+     (i32.const 1)
      (i32.add
       (local.get $0)
       (i32.const 24)
@@ -101,10 +93,7 @@
   )
   (drop
    (call $emscripten_asm_const_iii
-    (i32.add
-     (local.get $1)
-     (i32.const 2)
-    )
+    (i32.const 2)
     (i32.add
      (local.get $0)
      (i32.const 24)