[MC][X86] Enhance X86 Register expression handling to more closely match GCC.
Allow the comparison of x86 registers in the evaluation of assembler
directives. This generalizes and simplifies the extension from r334022
to catch another case found in the Linux kernel.
Reviewers: rnk, void
Reviewed By: rnk
Subscribers: hiraditya, nickdesaulniers, llvm-commits
Differential Revision: https://reviews.llvm.org/D50795
llvm-svn: 339895
diff --git a/llvm/lib/MC/MCExpr.cpp b/llvm/lib/MC/MCExpr.cpp
index e3a6f8e7..638cb35 100644
--- a/llvm/lib/MC/MCExpr.cpp
+++ b/llvm/lib/MC/MCExpr.cpp
@@ -751,8 +751,22 @@
if (!ABE->getLHS()->evaluateAsRelocatableImpl(LHSValue, Asm, Layout, Fixup,
Addrs, InSet) ||
!ABE->getRHS()->evaluateAsRelocatableImpl(RHSValue, Asm, Layout, Fixup,
- Addrs, InSet))
+ Addrs, InSet)) {
+ // Check if both are Target Expressions, see if we can compare them.
+ if (const MCTargetExpr *L = dyn_cast<MCTargetExpr>(ABE->getLHS()))
+ if (const MCTargetExpr *R = cast<MCTargetExpr>(ABE->getRHS())) {
+ switch (ABE->getOpcode()) {
+ case MCBinaryExpr::EQ:
+ Res = MCValue::get((L->isEqualTo(R)) ? -1 : 0);
+ return true;
+ case MCBinaryExpr::NE:
+ Res = MCValue::get((R->isEqualTo(R)) ? 0 : -1);
+ return true;
+ default: {}
+ }
+ }
return false;
+ }
// We only support a few operations on non-constant expressions, handle
// those first.