[MC] Change AsmParser to leverage Assembler during evaluation

Teach AsmParser to check with Assembler for when evaluating constant
expressions.  This improves the handing of preprocessor expressions
that must be resolved at parse time. This idiom can be found as
assembling-time assertion checks in source-level assemblers. Note that
this relies on the MCStreamer to keep sufficient tabs on Section /
Fragment information which the MCAsmStreamer does not. As a result the
textual output may fail where the equivalent object generation would
pass. This can most easily be resolved by folding the MCAsmStreamer
and MCObjectStreamer together which is planned for in a separate
patch.

Currently, this feature is only enabled for assembly input, keeping IR
compilation consistent between assembly and object generation.

Reviewers: echristo, rnk, probinson, espindola, peter.smith

Reviewed By: peter.smith

Subscribers: eraman, peter.smith, arichardson, jyknight, hiraditya, llvm-commits

Differential Revision: https://reviews.llvm.org/D45164

llvm-svn: 331218

1 files changed, 14 insertions, 0 deletions

diff --git a/llvm/test/MC/AsmParser/assembler-expressions-inlineasm.ll b/llvm/test/MC/AsmParser/assembler-expressions-inlineasm.ll
new file mode 100644
index 00000000000..35f110f37e2
--- /dev/null
+++ b/llvm/test/MC/AsmParser/assembler-expressions-inlineasm.ll
@@ -0,0 +1,14 @@
+; RUN: not llc -mtriple x86_64-unknown-linux-gnu -o %t.s -filetype=asm %s 2>&1 | FileCheck %s
+; RUN: not llc -mtriple x86_64-unknown-linux-gnu -o %t.o -filetype=obj %s 2>&1 | FileCheck %s
+
+; Assembler-aware expression evaluation should be disabled in inline
+; assembly to prevent differences in behavior between object and
+; assembly output.
+
+
+; CHECK: <inline asm>:1:17: error: expected absolute expression
+
+define i32 @main() local_unnamed_addr {
+  tail call void asm sideeffect "foo: nop;  .if . - foo==1;  nop;.endif", "~{dirflag},~{fpsr},~{flags}"()
+  ret i32 0
+}