[llvm] [RISCV] fixup_riscv_rvc_imm may be linker relaxable (PR #161797)

[via llvm-commits]

llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-backend-risc-v

Author: Sam Elliott (lenary)

<details>
<summary>Changes</summary>

With Xqcili, `c.li` may be relaxed to `qc.e.li` (this is because `qc.e.li` is compressed into `c.li`, which needs to be undone). `qc.e.li` is relaxable, so we need to mark `c.li` as linker relaxable when it is emitted.

This fixup cannot be emitted as a relocation, but we still mark it as requiring no R_RISCV_RELAX in case this changes in the future.

---
Full diff: https://github.com/llvm/llvm-project/pull/161797.diff


3 Files Affected:

- (modified) llvm/lib/Target/RISCV/MCTargetDesc/RISCVAsmBackend.cpp (+1) 
- (modified) llvm/lib/Target/RISCV/MCTargetDesc/RISCVMCCodeEmitter.cpp (+1) 
- (added) llvm/test/MC/RISCV/xqcili-linker-relaxation.s (+43) 


``````````diff
diff --git a/llvm/lib/Target/RISCV/MCTargetDesc/RISCVAsmBackend.cpp b/llvm/lib/Target/RISCV/MCTargetDesc/RISCVAsmBackend.cpp
index 41a9c92cf99c3..96e8afca0680e 100644
--- a/llvm/lib/Target/RISCV/MCTargetDesc/RISCVAsmBackend.cpp
+++ b/llvm/lib/Target/RISCV/MCTargetDesc/RISCVAsmBackend.cpp
@@ -823,6 +823,7 @@ static bool relaxableFixupNeedsRelocation(const MCFixupKind Kind) {
     break;
   case RISCV::fixup_riscv_rvc_jump:
   case RISCV::fixup_riscv_rvc_branch:
+  case RISCV::fixup_riscv_rvc_imm:
   case RISCV::fixup_riscv_jal:
     return false;
   }
diff --git a/llvm/lib/Target/RISCV/MCTargetDesc/RISCVMCCodeEmitter.cpp b/llvm/lib/Target/RISCV/MCTargetDesc/RISCVMCCodeEmitter.cpp
index 6d587e6f167fc..5934c91cb4b9a 100644
--- a/llvm/lib/Target/RISCV/MCTargetDesc/RISCVMCCodeEmitter.cpp
+++ b/llvm/lib/Target/RISCV/MCTargetDesc/RISCVMCCodeEmitter.cpp
@@ -688,6 +688,7 @@ uint64_t RISCVMCCodeEmitter::getImmOpValue(const MCInst &MI, unsigned OpNo,
       // the `jal` again in the assembler.
     } else if (MIFrm == RISCVII::InstFormatCI) {
       FixupKind = RISCV::fixup_riscv_rvc_imm;
+      AsmRelaxToLinkerRelaxableWithFeature(RISCV::FeatureVendorXqcili);
     } else if (MIFrm == RISCVII::InstFormatI) {
       FixupKind = RISCV::fixup_riscv_12_i;
     } else if (MIFrm == RISCVII::InstFormatQC_EB) {
diff --git a/llvm/test/MC/RISCV/xqcili-linker-relaxation.s b/llvm/test/MC/RISCV/xqcili-linker-relaxation.s
new file mode 100644
index 0000000000000..63bb17859776a
--- /dev/null
+++ b/llvm/test/MC/RISCV/xqcili-linker-relaxation.s
@@ -0,0 +1,43 @@
+
+# RUN: llvm-mc --triple=riscv32 -mattr=+relax,+experimental-xqcili \
+# RUN:    %s -filetype=obj -o - -riscv-add-build-attributes \
+# RUN:    | llvm-objdump -dr -M no-aliases - \
+# RUN:    | FileCheck %s
+
+## This tests that we correctly emit relocations for linker relaxation when
+## emitting `QC.E.LI` and `QC.LI`.
+
+  .section .text.ex1, "ax", @progbits
+  .global ex1
+ex1:
+# CHECK-LABEL: <ex1>:
+  blez    a1, .L1
+# CHECK-NEXT: bge zero, a1, 0x0 <ex1>
+# CHECK-NEXT: R_RISCV_BRANCH .L1{{$}}
+  qc.e.li a0, sym
+# CHECK-NEXT: qc.e.li a0, 0x0
+# CHECK-NEXT: R_RISCV_VENDOR QUALCOMM{{$}}
+# CHECK-NEXT: R_RISCV_CUSTOM194 sym{{$}}
+# CHECK-NEXT: R_RISCV_RELAX *ABS*{{$}}
+.L1:
+# CHECK: <.L1>:
+  ret
+# CHECK-NEXT: c.jr ra
+
+
+  .section .text.ex2, "ax", @progbits
+  .global ex2
+ex2:
+# CHECK-LABEL: <ex2>:
+  blez    a1, .L2
+# CHECK-NEXT: bge zero, a1, 0x0 <ex2>
+# CHECK-NEXT: R_RISCV_BRANCH .L2{{$}}
+  qc.li a0,  %qc.abs20(sym)
+# CHECK-NEXT: qc.li a0, 0x0
+# CHECK-NEXT: R_RISCV_VENDOR QUALCOMM{{$}}
+# CHECK-NEXT: R_RISCV_CUSTOM192 sym{{$}}
+# CHECK-NEXT: R_RISCV_RELAX *ABS*{{$}}
+.L2:
+# CHECK: <.L2>:
+  ret
+# CHECK-NEXT: c.jr ra

``````````

</details>


https://github.com/llvm/llvm-project/pull/161797