[llvm-branch-commits] [llvm] [LoongArch] Reduce number of reserved relocations when relax enabled (PR #153769)

[via llvm-branch-commits]

llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->
@llvm/pr-subscribers-mc

@llvm/pr-subscribers-backend-loongarch

Author: ZhaoQi (zhaoqi5)

<details>
<summary>Changes</summary>



---
Full diff: https://github.com/llvm/llvm-project/pull/153769.diff


2 Files Affected:

- (modified) llvm/lib/Target/LoongArch/MCTargetDesc/LoongArchAsmBackend.cpp (+9-18) 
- (modified) llvm/test/MC/LoongArch/Relocations/relax-attr.s (+4-3) 


``````````diff
diff --git a/llvm/lib/Target/LoongArch/MCTargetDesc/LoongArchAsmBackend.cpp b/llvm/lib/Target/LoongArch/MCTargetDesc/LoongArchAsmBackend.cpp
index ca5d27d54bb81..c6eda4fd63a6b 100644
--- a/llvm/lib/Target/LoongArch/MCTargetDesc/LoongArchAsmBackend.cpp
+++ b/llvm/lib/Target/LoongArch/MCTargetDesc/LoongArchAsmBackend.cpp
@@ -143,8 +143,6 @@ static void fixupLeb128(MCContext &Ctx, const MCFixup &Fixup, uint8_t *Data,
 void LoongArchAsmBackend::applyFixup(const MCFragment &F, const MCFixup &Fixup,
                                      const MCValue &Target, uint8_t *Data,
                                      uint64_t Value, bool IsResolved) {
-  if (IsResolved && shouldForceRelocation(Fixup, Target))
-    IsResolved = false;
   IsResolved = addReloc(F, Fixup, Target, Value, IsResolved);
   if (!Value)
     return; // Doesn't change encoding.
@@ -176,20 +174,6 @@ void LoongArchAsmBackend::applyFixup(const MCFragment &F, const MCFixup &Fixup,
   }
 }
 
-bool LoongArchAsmBackend::shouldForceRelocation(const MCFixup &Fixup,
-                                                const MCValue &Target) {
-  switch (Fixup.getKind()) {
-  default:
-    return STI.hasFeature(LoongArch::FeatureRelax);
-  case FK_Data_1:
-  case FK_Data_2:
-  case FK_Data_4:
-  case FK_Data_8:
-  case FK_Data_leb128:
-    return !Target.isAbsolute();
-  }
-}
-
 static inline std::pair<MCFixupKind, MCFixupKind>
 getRelocPairForSize(unsigned Size) {
   switch (Size) {
@@ -484,9 +468,16 @@ bool LoongArchAsmBackend::addReloc(const MCFragment &F, const MCFixup &Fixup,
     return false;
   }
 
-  IsResolved = Fallback();
   // If linker relaxation is enabled and supported by the current relocation,
-  // append a RELAX relocation.
+  // generate a relocation and then append a RELAX.
+  if (Fixup.isLinkerRelaxable())
+    IsResolved = false;
+  if (IsResolved && Fixup.isPCRel())
+    IsResolved = isPCRelFixupResolved(Target.getAddSym(), F);
+
+  if (!IsResolved)
+    Asm->getWriter().recordRelocation(F, Fixup, Target, FixedValue);
+
   if (Fixup.isLinkerRelaxable()) {
     auto FA = MCFixup::create(Fixup.getOffset(), nullptr, ELF::R_LARCH_RELAX);
     Asm->getWriter().recordRelocation(F, FA, MCValue::get(nullptr),
diff --git a/llvm/test/MC/LoongArch/Relocations/relax-attr.s b/llvm/test/MC/LoongArch/Relocations/relax-attr.s
index e3e9038b755d3..d94d32ebd7ab0 100644
--- a/llvm/test/MC/LoongArch/Relocations/relax-attr.s
+++ b/llvm/test/MC/LoongArch/Relocations/relax-attr.s
@@ -17,11 +17,8 @@
 # CHECKR-NEXT:     0x4 R_LARCH_CALL36 foo 0x0
 # CHECKR-NEXT:     0x4 R_LARCH_RELAX - 0x0
 # CHECKR-NEXT:     0x10 R_LARCH_B21 .L0 0x0
-# CHECKR-NEXT:     0x14 R_LARCH_B21 .L1 0x0
 # CHECKR-NEXT:     0x18 R_LARCH_B16 .L0 0x0
-# CHECKR-NEXT:     0x1C R_LARCH_B16 .L1 0x0
 # CHECKR-NEXT:     0x20 R_LARCH_B26 .L0 0x0
-# CHECKR-NEXT:     0x24 R_LARCH_B26 .L1 0x0
 # CHECKR-NEXT:   }
 # CHECKR-NEXT:   Section ({{.*}}) .rela.data {
 # CHECKR-NEXT:     0x0 R_LARCH_64 .L1 0x0
@@ -36,6 +33,10 @@
 
 .L1:
   nop
+## Relocations for branches to .L0 must be reserved and be fixed up by linker
+## when linker relaxation enabled, because of the relaxable call36 instruction.
+## Branches to .L1 can be resolved correctly at compile time, so their
+## relocations can simply be removed.
   bnez $a0, .L0
   beqz $a0, .L1
   beq  $a0, $a1, .L0

``````````

</details>


https://github.com/llvm/llvm-project/pull/153769