[RISCV] Collapse fast unaligned access into a single feature [nfc-ish] (#73971)

When we'd originally added unaligned-scalar-mem and
unaligned-vector-mem, they were separated into two parts under the
theory that some processor might implement one, but not the other. At
the moment, we don't have evidence of such a processor. The C/C++ level
interface, and the clang driver command lines have settled on a single
unaligned flag which indicates both scalar and vector support unaligned.
Given that, let's remove the test matrix complexity for a set of
configurations which don't appear useful.

Given these are internal feature names, I don't think we need to provide
any forward compatibility. Anyone disagree?

Note: The immediate trigger for this patch was finding another case
where the unaligned-vector-mem wasn't being properly serialized to IR
from clang which resulted in problems reproducing assembly from clang's
-emit-llvm feature. Instead of fixing this, I decided getting rid of the
complexity was the better approach.

1 files changed, 4 insertions, 9 deletions

diff --git a/llvm/lib/Target/RISCV/RISCVFeatures.td b/llvm/lib/Target/RISCV/RISCVFeatures.td
index c5d88ca..7d142d3 100644
--- a/llvm/lib/Target/RISCV/RISCVFeatures.td
+++ b/llvm/lib/Target/RISCV/RISCVFeatures.td
@@ -946,15 +946,10 @@ def FeatureTrailingSeqCstFence : SubtargetFeature<"seq-cst-trailing-fence",
                                           "true",
                                           "Enable trailing fence for seq-cst store.">;
 
-def FeatureUnalignedScalarMem
-   : SubtargetFeature<"unaligned-scalar-mem", "EnableUnalignedScalarMem",
-                      "true", "Has reasonably performant unaligned scalar "
-                      "loads and stores">;
-
-def FeatureUnalignedVectorMem
-   : SubtargetFeature<"unaligned-vector-mem", "EnableUnalignedVectorMem",
-                      "true", "Has reasonably performant unaligned vector "
-                      "loads and stores">;
+def FeatureFastUnalignedAccess
+   : SubtargetFeature<"fast-unaligned-access", "HasFastUnalignedAccess",
+                      "true", "Has reasonably performant unaligned "
+                      "loads and stores (both scalar and vector)">;
 
 def FeaturePostRAScheduler : SubtargetFeature<"use-postra-scheduler",
     "UsePostRAScheduler", "true", "Schedule again after register allocation">;