[X86][MC] Fix assembling rip-relative addressing + immediate displacements

In the rare case where the input contains rip-relative addressing with
immediate displacements, *and* the instruction ends with an immediate,
we encode the instruction in the wrong way:

movl $12345678, 0x400(%rdi) // all good, no rip-relative addr
movl %eax, 0x400(%rip) // all good, no immediate at the end of the instruction
movl $12345678, 0x400(%rip) // fails, encodes address as 0x3fc(%rip)

Offset is a label:

movl $12345678, foo(%rip)

we want to account for the size of the immediate (in this case,
$12345678, 4 bytes).

Offset is an immediate:

movl $12345678, 0x400(%rip)

we should not account for the size of the immediate, assuming the
immediate offset is what the user wanted.

Differential Revision: https://reviews.llvm.org/D43050

llvm-svn: 324772

1 files changed, 7 insertions, 3 deletions

diff --git a/llvm/lib/Target/X86/MCTargetDesc/X86MCCodeEmitter.cpp b/llvm/lib/Target/X86/MCTargetDesc/X86MCCodeEmitter.cpp
index a7059c6914d..4ddc1f0ba42 100644
--- a/llvm/lib/Target/X86/MCTargetDesc/X86MCCodeEmitter.cpp
+++ b/llvm/lib/Target/X86/MCTargetDesc/X86MCCodeEmitter.cpp
@@ -396,10 +396,14 @@ void X86MCCodeEmitter::emitMemModRMByte(const MCInst &MI, unsigned Op,
 
     // rip-relative addressing is actually relative to the *next* instruction.
     // Since an immediate can follow the mod/rm byte for an instruction, this
-    // means that we need to bias the immediate field of the instruction with
-    // the size of the immediate field.  If we have this case, add it into the
+    // means that we need to bias the displacement field of the instruction with
+    // the size of the immediate field. If we have this case, add it into the
     // expression to emit.
-    int ImmSize = X86II::hasImm(TSFlags) ? X86II::getSizeOfImm(TSFlags) : 0;
+    // Note: rip-relative addressing using immediate displacement values should
+    // not be adjusted, assuming it was the user's intent.
+    int ImmSize = !Disp.isImm() && X86II::hasImm(TSFlags)
+                      ? X86II::getSizeOfImm(TSFlags)
+                      : 0;
 
     EmitImmediate(Disp, MI.getLoc(), 4, MCFixupKind(FixupKind),
                   CurByte, OS, Fixups, -ImmSize);