[llvm] [XCOFF] make related SD symbols as isFunction (PR #69553)

[James Henderson via llvm-commits]

================
@@ -1242,25 +1242,55 @@ bool XCOFFSymbolRef::isFunction() const {
 
   const XCOFFCsectAuxRef CsectAuxRef = ExpCsectAuxEnt.get();
 
-  // A function definition should be a label definition.
-  // FIXME: This is not necessarily the case when -ffunction-sections is
-  // enabled.
-  if (!CsectAuxRef.isLabel())
+  if (CsectAuxRef.getStorageMappingClass() != XCOFF::XMC_PR &&
+      CsectAuxRef.getStorageMappingClass() != XCOFF::XMC_GL)
     return false;
 
-  if (CsectAuxRef.getStorageMappingClass() != XCOFF::XMC_PR)
+  // A function definition should not be a common type symbol or a external
+  // symbol.
+  if (CsectAuxRef.getSymbolType() == XCOFF::XTY_CM ||
+      CsectAuxRef.getSymbolType() == XCOFF::XTY_ER)
     return false;
 
-  const int16_t SectNum = getSectionNumber();
-  Expected<DataRefImpl> SI = getObject()->getSectionByNum(SectNum);
-  if (!SI) {
-    // If we could not get the section, then this symbol should not be
-    // a function. So consume the error and return `false` to move on.
-    consumeError(SI.takeError());
-    return false;
+  // If the next symbol is a XTY_LD type symbol with same address, this XTY_SD
+  // symbol is not a function. Otherwise this is a function symbol for
+  // -ffunction-sections.
+  if (CsectAuxRef.getSymbolType() == XCOFF::XTY_SD) {
+    // If this is a csect with size 0, it won't be a function definition.
+    // This is used to hack situation that llvm always generates below symbol
+    // for -ffunction-sections:
+    // m   0x00000000     .text     1  unamex                    **No Symbol**
+    // a4  0x00000000       0    0     SD       PR    0    0
+    if (getSize() == 0)
+      return false;
+
+    xcoff_symbol_iterator NextIt(this);
+    // If this is the last main symbol table entry, there won't be XTY_LD type
----------------
jh7370 wrote:

```suggestion
    // If this is the last main symbol table entry, there won't be an XTY_LD type
```

https://github.com/llvm/llvm-project/pull/69553