[RISCV] Insert R_RISCV_ALIGN relocation type and Nops for code alignment when linker relaxation enabled

Linker relaxation may change code size. We need to fix up the alignment
of alignment directive in text section by inserting Nops and R_RISCV_ALIGN
relocation type. So then linker could satisfy the alignment by removing Nops.

To do this:

1. Add shouldInsertExtraNopBytesForCodeAlign target hook to calculate
   the Nops we need to insert.

2. Add shouldInsertFixupForCodeAlign target hook to insert
   R_RISCV_ALIGN fixup type.

Differential Revision: https://reviews.llvm.org/D47755

llvm-svn: 352616

1 files changed, 16 insertions, 1 deletions

diff --git a/llvm/lib/MC/MCAssembler.cpp b/llvm/lib/MC/MCAssembler.cpp
index 8a46699305a..c4f4d4c2870 100644
--- a/llvm/lib/MC/MCAssembler.cpp
+++ b/llvm/lib/MC/MCAssembler.cpp
@@ -322,6 +322,13 @@ uint64_t MCAssembler::computeFragmentSize(const MCAsmLayout &Layout,
     const MCAlignFragment &AF = cast<MCAlignFragment>(F);
     unsigned Offset = Layout.getFragmentOffset(&AF);
     unsigned Size = OffsetToAlignment(Offset, AF.getAlignment());
+
+    // Insert extra Nops for code alignment if the target define
+    // shouldInsertExtraNopBytesForCodeAlign target hook.
+    if (AF.getParent()->UseCodeAlign() && AF.hasEmitNops() &&
+        getBackend().shouldInsertExtraNopBytesForCodeAlign(AF, Size))
+      return Size;
+
     // If we are padding with nops, force the padding to be larger than the
     // minimum nop size.
     if (Size > 0 && AF.hasEmitNops()) {
@@ -804,7 +811,8 @@ void MCAssembler::layout(MCAsmLayout &Layout) {
       if (isa<MCEncodedFragment>(&Frag) &&
           isa<MCCompactEncodedInstFragment>(&Frag))
         continue;
-      if (!isa<MCEncodedFragment>(&Frag) && !isa<MCCVDefRangeFragment>(&Frag))
+      if (!isa<MCEncodedFragment>(&Frag) && !isa<MCCVDefRangeFragment>(&Frag) &&
+          !isa<MCAlignFragment>(&Frag))
         continue;
       ArrayRef<MCFixup> Fixups;
       MutableArrayRef<char> Contents;
@@ -825,6 +833,13 @@ void MCAssembler::layout(MCAsmLayout &Layout) {
       } else if (auto *FragWithFixups = dyn_cast<MCDwarfLineAddrFragment>(&Frag)) {
         Fixups = FragWithFixups->getFixups();
         Contents = FragWithFixups->getContents();
+      } else if (auto *AF = dyn_cast<MCAlignFragment>(&Frag)) {
+        // Insert fixup type for code alignment if the target define
+        // shouldInsertFixupForCodeAlign target hook.
+        if (Sec.UseCodeAlign() && AF->hasEmitNops()) {
+          getBackend().shouldInsertFixupForCodeAlign(*this, Layout, *AF);
+        }
+        continue;
       } else
         llvm_unreachable("Unknown fragment with fixups!");
       for (const MCFixup &Fixup : Fixups) {