[RISCV] Remove mayLoad = 1 from store-conditional

[francisvm]

lr.[wd]: mayLoad = 1, mayStore = 0
sc.[wd]: mayLoad = 0, mayStore = 1

all other AMOs: mayLoad = 1, mayStore = 1

[llvmbot]

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

Author: Francis Visoiu Mistrih (francisvm)

Changes

lr.[wd]: mayLoad = 1, mayStore = 0
sc.[wd]: mayLoad = 0, mayStore = 1

all other AMOs: mayLoad = 1, mayStore = 1

---

Full diff: https://github.com/llvm/llvm-project/pull/88470.diff

1 Files Affected:

• (modified) llvm/lib/Target/RISCV/RISCVInstrInfoA.td (+15-2)

diff --git a/llvm/lib/Target/RISCV/RISCVInstrInfoA.td b/llvm/lib/Target/RISCV/RISCVInstrInfoA.td
index 36842ceb49bfb8..814e0ddf111e63 100644
--- a/llvm/lib/Target/RISCV/RISCVInstrInfoA.td
+++ b/llvm/lib/Target/RISCV/RISCVInstrInfoA.td
@@ -30,6 +30,19 @@ multiclass LR_r_aq_rl<bits<3> funct3, string opcodestr> {
   def _AQ_RL : LR_r<1, 1, funct3, opcodestr # ".aqrl">;
 }
 
+let hasSideEffects = 0, mayLoad = 0, mayStore = 1 in
+class SC_r<bit aq, bit rl, bits<3> funct3, string opcodestr>
+    : RVInstRAtomic<0b00011, aq, rl, funct3, OPC_AMO,
+                    (outs GPR:$rd), (ins GPRMemZeroOffset:$rs1, GPR:$rs2),
+                    opcodestr, "$rd, $rs2, $rs1">;
+
+multiclass SC_r_aq_rl<bits<3> funct3, string opcodestr> {
+  def ""     : SC_r<0, 0, funct3, opcodestr>;
+  def _AQ    : SC_r<1, 0, funct3, opcodestr # ".aq">;
+  def _RL    : SC_r<0, 1, funct3, opcodestr # ".rl">;
+  def _AQ_RL : SC_r<1, 1, funct3, opcodestr # ".aqrl">;
+}
+
 let hasSideEffects = 0, mayLoad = 1, mayStore = 1 in
 class AMO_rr<bits<5> funct5, bit aq, bit rl, bits<3> funct3, string opcodestr>
     : RVInstRAtomic<funct5, aq, rl, funct3, OPC_AMO,
@@ -49,7 +62,7 @@ multiclass AMO_rr_aq_rl<bits<5> funct5, bits<3> funct3, string opcodestr> {
 
 let Predicates = [HasStdExtAOrZalrsc], IsSignExtendingOpW = 1 in {
 defm LR_W       : LR_r_aq_rl<0b010, "lr.w">, Sched<[WriteAtomicLDW, ReadAtomicLDW]>;
-defm SC_W       : AMO_rr_aq_rl<0b00011, 0b010, "sc.w">,
+defm SC_W       : SC_r_aq_rl<0b010, "sc.w">,
                   Sched<[WriteAtomicSTW, ReadAtomicSTW, ReadAtomicSTW]>;
 } // Predicates = [HasStdExtAOrZalrsc], IsSignExtendingOpW = 1
 
@@ -76,7 +89,7 @@ defm AMOMAXU_W  : AMO_rr_aq_rl<0b11100, 0b010, "amomaxu.w">,
 
 let Predicates = [HasStdExtAOrZalrsc, IsRV64] in {
 defm LR_D       : LR_r_aq_rl<0b011, "lr.d">, Sched<[WriteAtomicLDD, ReadAtomicLDD]>;
-defm SC_D       : AMO_rr_aq_rl<0b00011, 0b011, "sc.d">,
+defm SC_D       : SC_r_aq_rl<0b011, "sc.d">,
                   Sched<[WriteAtomicSTD, ReadAtomicSTD, ReadAtomicSTD]>;
 } // Predicates = [HasStdExtAOrZalrsc, IsRV64]
 

[topperc]

Does this have any functional effect? Atomic expansion runs so late, I'm thinking it doesn't.

[wangpc-pp]

I think it's OK.
LGTM.

[francisvm]

Does this have any functional effect? Atomic expansion runs so late, I'm thinking it doesn't.

You’re right, it doesn’t. We were playing with exposing an intrinsic and saw the wrong field by chance.