[llvm] [X86] Disallow immediate address calls when position independent (PR #202370)

[Rui Ueyama via llvm-commits]

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@@ -241,7 +241,7 @@ bool X86Subtarget::isLegalToCallImmediateAddr() const {
   // FIXME: I386 PE/COFF supports PC relative calls using IMAGE_REL_I386_REL32
   // but WinCOFFObjectWriter::RecordRelocation cannot emit them.  Once it does,
   // the following check for Win32 should be removed.
-  if (Is64Bit || isTargetWin32())
+  if (Is64Bit || isTargetWin32() || isPositionIndependent())
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rui314 wrote:

Not sure I fully understand the question, but my understanding is that this change makes the backend emit something like `mov imm32, %reg; call *%reg` instead of `call imm32` when the callee is an immediate address and the output is position-independent.

My understanding is that is exactly what we want here: on i386, the immediate operand of `call imm32` is a PC-relative displacement from the next instruction, not an absolute address. In PIC/PIE, that's not representable, so we always have to use a register-indirect call instruction.

https://github.com/llvm/llvm-project/pull/202370