[RISCV] Fix crash for section alignment with .option norvc

The existing code wasn't getting the subtarget info from the fragment,
so the current status of RVC would be ignored. This would cause a crash
for the new test case when the target then reported it couldn't write
the requested number of code alignment bytes.

Differential Revision: https://reviews.llvm.org/D122236

(cherry picked from commit d09d297c)

llvm/lib/Target/RISCV/MCTargetDesc/RISCVAsmBackend.cpp

@@ -583,10 +583,11 @@ void RISCVAsmBackend::applyFixup(const MCAssembler &Asm, const MCFixup &Fixup,
 bool RISCVAsmBackend::shouldInsertExtraNopBytesForCodeAlign(
     const MCAlignFragment &AF, unsigned &Size) {
   // Calculate Nops Size only when linker relaxation enabled.
-  if (!STI.getFeatureBits()[RISCV::FeatureRelax])
+  const MCSubtargetInfo *STI = AF.getSubtargetInfo();
+  if (!STI->getFeatureBits()[RISCV::FeatureRelax])
     return false;
 
-  bool HasStdExtC = STI.getFeatureBits()[RISCV::FeatureStdExtC];
+  bool HasStdExtC = STI->getFeatureBits()[RISCV::FeatureStdExtC];
   unsigned MinNopLen = HasStdExtC ? 2 : 4;
 
   if (AF.getAlignment() <= MinNopLen) {
@@ -606,7 +607,8 @@ bool RISCVAsmBackend::shouldInsertFixupForCodeAlign(MCAssembler &Asm,
                                                     const MCAsmLayout &Layout,
                                                     MCAlignFragment &AF) {
   // Insert the fixup only when linker relaxation enabled.
-  if (!STI.getFeatureBits()[RISCV::FeatureRelax])
+  const MCSubtargetInfo *STI = AF.getSubtargetInfo();
+  if (!STI->getFeatureBits()[RISCV::FeatureRelax])
     return false;
 
   // Calculate total Nops we need to insert. If there are none to insert

llvm/test/MC/RISCV/align-option-relax.s

+# RUN: llvm-mc -filetype=obj -triple riscv32 -mattr=-relax < %s \
+# RUN:     | llvm-readobj -r - | FileCheck %s
+
+# Check that .option relax overrides -mno-relax and enables R_RISCV_ALIGN
+# relocations.
+# CHECK: R_RISCV_ALIGN
+	.option relax
+	.align 4

llvm/test/MC/RISCV/align.s

@@ -112,3 +112,11 @@ data1:
 # C-EXT-RELAX-RELOC-NOT: R_RISCV_ALIGN
 data2:
 	.word 9
+# Check that the initial alignment is properly handled when using .option to
+# disable the C extension. This used to crash.
+# C-EXT-RELAX-INST:      <.text2>:
+# C-EXT-RELAX-INST-NEXT: add a0, a0, a1
+	.section .text2, "x"
+	.option norvc
+	.balign 4
+	add	a0, a0, a1