From 3d89fb4d13bc3af1c3643a310b90fce51a649119 Mon Sep 17 00:00:00 2001
From: Fangrui Song <i@maskray.me>
Date: Tue, 13 Jul 2021 09:30:09 -0700
Subject: [PATCH] [RISCV] Support machine constraint "S"

Similar to D46745, "S" represents an absolute symbolic operand, which
can be used to specify the access models, e.g.

  extern int var;
  void *addr_via_asm() {
    void *ret;
    asm("lui %0, %%hi(%1)\naddi %0,%0,%%lo(%1)" : "=r"(ret) : "S"(&var));
    return ret;
  }

'S' is documented in trunk GCC: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101275

Reviewed By: luismarques

Differential Revision: https://reviews.llvm.org/D105254
---
 clang/lib/Basic/Targets/RISCV.cpp                  |  3 ++
 clang/test/CodeGen/RISCV/riscv-inline-asm.c        |  6 +++
 llvm/lib/Target/RISCV/RISCVISelLowering.cpp        | 11 +++++
 llvm/test/CodeGen/RISCV/inline-asm-S-constraint.ll | 54 ++++++++++++++++++++++
 4 files changed, 74 insertions(+)
 create mode 100644 llvm/test/CodeGen/RISCV/inline-asm-S-constraint.ll

diff --git a/clang/lib/Basic/Targets/RISCV.cpp b/clang/lib/Basic/Targets/RISCV.cpp
index 1f31f47..9705129 100644
--- a/clang/lib/Basic/Targets/RISCV.cpp
+++ b/clang/lib/Basic/Targets/RISCV.cpp
@@ -87,6 +87,9 @@ bool RISCVTargetInfo::validateAsmConstraint(
     // An address that is held in a general-purpose register.
     Info.setAllowsMemory();
     return true;
+  case 'S': // A symbolic address
+    Info.setAllowsRegister();
+    return true;
   case 'v':
     // A vector register.
     if (Name[1] == 'r' || Name[1] == 'm') {
diff --git a/clang/test/CodeGen/RISCV/riscv-inline-asm.c b/clang/test/CodeGen/RISCV/riscv-inline-asm.c
index dea900f..2303293 100644
--- a/clang/test/CodeGen/RISCV/riscv-inline-asm.c
+++ b/clang/test/CodeGen/RISCV/riscv-inline-asm.c
@@ -44,3 +44,9 @@ void test_A(int *p) {
 // CHECK: call void asm sideeffect "", "*A"(i32* %p)
   asm volatile("" :: "A"(*p));
 }
+
+void test_S() {
+// CHECK-LABEL: define{{.*}} void @test_S()
+// CHECK: call void asm sideeffect "", "S"(float* nonnull @f)
+  asm volatile("" :: "S"(&f));
+}
diff --git a/llvm/lib/Target/RISCV/RISCVISelLowering.cpp b/llvm/lib/Target/RISCV/RISCVISelLowering.cpp
index ab0d018..a81aec1 100644
--- a/llvm/lib/Target/RISCV/RISCVISelLowering.cpp
+++ b/llvm/lib/Target/RISCV/RISCVISelLowering.cpp
@@ -8294,6 +8294,8 @@ RISCVTargetLowering::getConstraintType(StringRef Constraint) const {
       return C_Immediate;
     case 'A':
       return C_Memory;
+    case 'S': // A symbolic address
+      return C_Other;
     }
   }
   return TargetLowering::getConstraintType(Constraint);
@@ -8523,6 +8525,15 @@ void RISCVTargetLowering::LowerAsmOperandForConstraint(
               DAG.getTargetConstant(CVal, SDLoc(Op), Subtarget.getXLenVT()));
       }
       return;
+    case 'S':
+      if (const auto *GA = dyn_cast<GlobalAddressSDNode>(Op)) {
+        Ops.push_back(DAG.getTargetGlobalAddress(GA->getGlobal(), SDLoc(Op),
+                                                 GA->getValueType(0)));
+      } else if (const auto *BA = dyn_cast<BlockAddressSDNode>(Op)) {
+        Ops.push_back(DAG.getTargetBlockAddress(BA->getBlockAddress(),
+                                                BA->getValueType(0)));
+      }
+      return;
     default:
       break;
     }
diff --git a/llvm/test/CodeGen/RISCV/inline-asm-S-constraint.ll b/llvm/test/CodeGen/RISCV/inline-asm-S-constraint.ll
new file mode 100644
index 0000000..2387978
--- /dev/null
+++ b/llvm/test/CodeGen/RISCV/inline-asm-S-constraint.ll
@@ -0,0 +1,54 @@
+; NOTE: Assertions have been autogenerated by utils/update_llc_test_checks.py
+; RUN: llc -mtriple=riscv32 < %s | FileCheck %s --check-prefix=RV32
+; RUN: llc -mtriple=riscv64 < %s | FileCheck %s --check-prefix=RV64
+
+@var = external dso_local global i32, align 4
+
+define dso_local i8* @constraint_S() {
+; RV32-LABEL: constraint_S:
+; RV32:       # %bb.0:
+; RV32-NEXT:    #APP
+; RV32-NEXT:    lui a0, %hi(var)
+; RV32-NEXT:    addi a0, a0, %lo(var)
+; RV32-NEXT:    #NO_APP
+; RV32-NEXT:    ret
+;
+; RV64-LABEL: constraint_S:
+; RV64:       # %bb.0:
+; RV64-NEXT:    #APP
+; RV64-NEXT:    lui a0, %hi(var)
+; RV64-NEXT:    addi a0, a0, %lo(var)
+; RV64-NEXT:    #NO_APP
+; RV64-NEXT:    ret
+  %ret = tail call i8* asm "lui $0, %hi($1)\0Aaddi $0, $0, %lo($1)", "=r,S"(i32* nonnull @var)
+  ret i8* %ret
+}
+
+; Function Attrs: nofree nosync nounwind readnone
+define dso_local i8* @constraint_S_label() {
+; RV32-LABEL: constraint_S_label:
+; RV32:       # %bb.0: # %entry
+; RV32-NEXT:  .Ltmp0: # Block address taken
+; RV32-NEXT:  # %bb.1: # %L1
+; RV32-NEXT:    #APP
+; RV32-NEXT:    lui a0, %hi(.Ltmp0)
+; RV32-NEXT:    addi a0, a0, %lo(.Ltmp0)
+; RV32-NEXT:    #NO_APP
+; RV32-NEXT:    ret
+;
+; RV64-LABEL: constraint_S_label:
+; RV64:       # %bb.0: # %entry
+; RV64-NEXT:  .Ltmp0: # Block address taken
+; RV64-NEXT:  # %bb.1: # %L1
+; RV64-NEXT:    #APP
+; RV64-NEXT:    lui a0, %hi(.Ltmp0)
+; RV64-NEXT:    addi a0, a0, %lo(.Ltmp0)
+; RV64-NEXT:    #NO_APP
+; RV64-NEXT:    ret
+entry:
+  br label %L1
+
+L1:
+  %ret = tail call i8* asm "lui $0, %hi($1)\0Aaddi $0, $0, %lo($1)", "=r,S"(i8* blockaddress(@constraint_S_label, %L1))
+  ret i8* %ret
+}
-- 
2.7.4