[llvm] b7f97d3 - [RISCV] Place mergeable small read only data into srodata section (#82214)

[via llvm-commits]

Author: Kito Cheng
Date: 2024-03-11T13:57:06+08:00
New Revision: b7f97d3661814c4ae11b8772f8a27c029d01648b

URL: https://github.com/llvm/llvm-project/commit/b7f97d3661814c4ae11b8772f8a27c029d01648b
DIFF: https://github.com/llvm/llvm-project/commit/b7f97d3661814c4ae11b8772f8a27c029d01648b.diff

LOG: [RISCV] Place mergeable small read only data into srodata section (#82214)

Small mergeable read only data was place on the sdata before, but it
also means it lose the mergeable property, which means lose some code
size optimization opportunity during link time.

Added: 
    llvm/test/CodeGen/RISCV/srodata.ll

Modified: 
    llvm/lib/Target/RISCV/RISCVTargetObjectFile.cpp
    llvm/lib/Target/RISCV/RISCVTargetObjectFile.h

Removed: 
    


################################################################################
diff  --git a/llvm/lib/Target/RISCV/RISCVTargetObjectFile.cpp b/llvm/lib/Target/RISCV/RISCVTargetObjectFile.cpp
index 1535149b919b55..e7c1a7e5d8bca1 100644
--- a/llvm/lib/Target/RISCV/RISCVTargetObjectFile.cpp
+++ b/llvm/lib/Target/RISCV/RISCVTargetObjectFile.cpp
@@ -32,6 +32,16 @@ void RISCVELFTargetObjectFile::Initialize(MCContext &Ctx,
       ".sdata", ELF::SHT_PROGBITS, ELF::SHF_WRITE | ELF::SHF_ALLOC);
   SmallBSSSection = getContext().getELFSection(".sbss", ELF::SHT_NOBITS,
                                                ELF::SHF_WRITE | ELF::SHF_ALLOC);
+  SmallRODataSection =
+      getContext().getELFSection(".srodata", ELF::SHT_PROGBITS, ELF::SHF_ALLOC);
+  SmallROData4Section = getContext().getELFSection(
+      ".srodata.cst4", ELF::SHT_PROGBITS, ELF::SHF_ALLOC | ELF::SHF_MERGE, 4);
+  SmallROData8Section = getContext().getELFSection(
+      ".srodata.cst8", ELF::SHT_PROGBITS, ELF::SHF_ALLOC | ELF::SHF_MERGE, 8);
+  SmallROData16Section = getContext().getELFSection(
+      ".srodata.cst16", ELF::SHT_PROGBITS, ELF::SHF_ALLOC | ELF::SHF_MERGE, 16);
+  SmallROData32Section = getContext().getELFSection(
+      ".srodata.cst32", ELF::SHT_PROGBITS, ELF::SHF_ALLOC | ELF::SHF_MERGE, 32);
 }
 
 const MCExpr *RISCVELFTargetObjectFile::getIndirectSymViaGOTPCRel(
@@ -126,8 +136,19 @@ bool RISCVELFTargetObjectFile::isConstantInSmallSection(
 MCSection *RISCVELFTargetObjectFile::getSectionForConstant(
     const DataLayout &DL, SectionKind Kind, const Constant *C,
     Align &Alignment) const {
-  if (isConstantInSmallSection(DL, C))
-    return SmallDataSection;
+  if (isConstantInSmallSection(DL, C)) {
+    if (Kind.isMergeableConst4())
+      return SmallROData4Section;
+    if (Kind.isMergeableConst8())
+      return SmallROData8Section;
+    if (Kind.isMergeableConst16())
+      return SmallROData16Section;
+    if (Kind.isMergeableConst32())
+      return SmallROData32Section;
+    // LLVM only generate up to .rodata.cst32, and use .rodata section if more
+    // than 32 bytes, so just use .srodata here.
+    return SmallRODataSection;
+  }
 
   // Otherwise, we work the same as ELF.
   return TargetLoweringObjectFileELF::getSectionForConstant(DL, Kind, C,

diff  --git a/llvm/lib/Target/RISCV/RISCVTargetObjectFile.h b/llvm/lib/Target/RISCV/RISCVTargetObjectFile.h
index 0910fbd3d95041..05e61ac874abba 100644
--- a/llvm/lib/Target/RISCV/RISCVTargetObjectFile.h
+++ b/llvm/lib/Target/RISCV/RISCVTargetObjectFile.h
@@ -16,6 +16,11 @@ namespace llvm {
 /// This implementation is used for RISC-V ELF targets.
 class RISCVELFTargetObjectFile : public TargetLoweringObjectFileELF {
   MCSection *SmallDataSection;
+  MCSection *SmallRODataSection;
+  MCSection *SmallROData4Section;
+  MCSection *SmallROData8Section;
+  MCSection *SmallROData16Section;
+  MCSection *SmallROData32Section;
   MCSection *SmallBSSSection;
   unsigned SSThreshold = 8;
 

diff  --git a/llvm/test/CodeGen/RISCV/srodata.ll b/llvm/test/CodeGen/RISCV/srodata.ll
new file mode 100644
index 00000000000000..1d5bd904f233fe
--- /dev/null
+++ b/llvm/test/CodeGen/RISCV/srodata.ll
@@ -0,0 +1,47 @@
+; RUN: sed 's/SMALL_DATA_LIMIT/0/g' %s | \
+; RUN:   llc -mtriple=riscv32 -mattr=+d | \
+; RUN:   FileCheck -check-prefix=CHECK-SDL-0 %s
+; RUN: sed 's/SMALL_DATA_LIMIT/0/g' %s | \
+; RUN:   llc -mtriple=riscv64 -mattr=+d | \
+; RUN:   FileCheck -check-prefix=CHECK-SDL-0 %s
+; RUN: sed 's/SMALL_DATA_LIMIT/4/g' %s | \
+; RUN:   llc -mtriple=riscv32 -mattr=+d | \
+; RUN:   FileCheck -check-prefix=CHECK-SDL-4 %s
+; RUN: sed 's/SMALL_DATA_LIMIT/4/g' %s | \
+; RUN:   llc -mtriple=riscv64 -mattr=+d | \
+; RUN:   FileCheck -check-prefix=CHECK-SDL-4 %s
+; RUN: sed 's/SMALL_DATA_LIMIT/8/g' %s | \
+; RUN:   llc -mtriple=riscv32 -mattr=+d | \
+; RUN:   FileCheck -check-prefix=CHECK-SDL-8 %s
+; RUN: sed 's/SMALL_DATA_LIMIT/8/g' %s | \
+; RUN:   llc -mtriple=riscv64 -mattr=+d | \
+; RUN:   FileCheck -check-prefix=CHECK-SDL-8 %s
+; RUN: sed 's/SMALL_DATA_LIMIT/16/g' %s | \
+; RUN:   llc -mtriple=riscv32 -mattr=+d | \
+; RUN:   FileCheck -check-prefix=CHECK-SDL-16 %s
+; RUN: sed 's/SMALL_DATA_LIMIT/16/g' %s | \
+; RUN:   llc -mtriple=riscv64 -mattr=+d | \
+; RUN:   FileCheck -check-prefix=CHECK-SDL-16 %s
+
+define dso_local float @foof() {
+entry:
+  ret float 0x400A08ACA0000000
+}
+
+define dso_local double @foo() {
+entry:
+  ret double 0x400A08AC91C3E242
+}
+
+!llvm.module.flags = !{!0}
+
+!0 = !{i32 8, !"SmallDataLimit", i32 SMALL_DATA_LIMIT}
+
+; CHECK-SDL-0-NOT:    .section        .srodata.cst4
+; CHECK-SDL-0-NOT:    .section        .srodata.cst8
+; CHECK-SDL-4:        .section        .srodata.cst4
+; CHECK-SDL-4-NOT:    .section        .srodata.cst8
+; CHECK-SDL-8:        .section        .srodata.cst4
+; CHECK-SDL-8:        .section        .srodata.cst8
+; CHECK-SDL-16:       .section        .srodata.cst4
+; CHECK-SDL-16:       .section        .srodata.cst8