[RISCV][GISel] Use LBU for anyext i8 atomic_load. (#161588)

topperc · web-flow · commit 129d5ce14c4f · 2025-10-01T19:55:46.000-07:00
This matches what we do for regular i8 extload due to the lack of c.lb
in Zbc.

This only affects global isel because SelectionDAG won't create an
anyext i8 atomic_load today.
diff --git a/llvm/lib/Target/RISCV/RISCVGISel.td b/llvm/lib/Target/RISCV/RISCVGISel.td
@@ -109,8 +109,9 @@ def : LdPat<extloadi8, LBU, i16>; // Prefer unsigned due to no c.lb in Zcb.
 def : StPat<truncstorei8, SB, GPR, i16>;
 
 let Predicates = [HasAtomicLdSt] in {
-  def : LdPat<atomic_load_aext_8,  LB, i16>;
-  def : LdPat<atomic_load_nonext_16, LH, i16>;
+  // Prefer unsigned due to no c.lb in Zcb.
+  def : LdPat<atomic_load_aext_8,    LBU, i16>;
+  def : LdPat<atomic_load_nonext_16, LH,  i16>;
 
   def : StPat<atomic_store_8,  SB, GPR, i16>;
   def : StPat<atomic_store_16, SH, GPR, i16>;
diff --git a/llvm/lib/Target/RISCV/RISCVInstrInfoA.td b/llvm/lib/Target/RISCV/RISCVInstrInfoA.td
@@ -165,10 +165,11 @@ class seq_cst_store<PatFrag base>
 // any ordering. This is necessary because AtomicExpandPass has added fences to
 // atomic load/stores and changed them to unordered ones.
 let Predicates = [HasAtomicLdSt] in {
-  def : LdPat<relaxed_load<atomic_load_asext_8>,  LB>;
+  // Use unsigned for aext due to no c.lb in Zcb.
+  def : LdPat<relaxed_load<atomic_load_sext_8>,   LB>;
+  def : LdPat<relaxed_load<atomic_load_azext_8>,  LBU>;
   def : LdPat<relaxed_load<atomic_load_asext_16>, LH>;
-  def : LdPat<relaxed_load<atomic_load_zext_8>,  LBU>;
-  def : LdPat<relaxed_load<atomic_load_zext_16>, LHU>;
+  def : LdPat<relaxed_load<atomic_load_zext_16>,  LHU>;
 
   def : StPat<relaxed_store<atomic_store_8>,  SB, GPR, XLenVT>;
   def : StPat<relaxed_store<atomic_store_16>, SH, GPR, XLenVT>;
diff --git a/llvm/test/CodeGen/RISCV/GlobalISel/atomic-load-store.ll b/llvm/test/CodeGen/RISCV/GlobalISel/atomic-load-store.ll
@@ -37,7 +37,7 @@ define i8 @atomic_load_i8_unordered(ptr %a) nounwind {
 ;
 ; RV32IA-LABEL: atomic_load_i8_unordered:
 ; RV32IA:       # %bb.0:
-; RV32IA-NEXT:    lb a0, 0(a0)
+; RV32IA-NEXT:    lbu a0, 0(a0)
 ; RV32IA-NEXT:    ret
 ;
 ; RV64I-LABEL: atomic_load_i8_unordered:
@@ -52,7 +52,7 @@ define i8 @atomic_load_i8_unordered(ptr %a) nounwind {
 ;
 ; RV64IA-LABEL: atomic_load_i8_unordered:
 ; RV64IA:       # %bb.0:
-; RV64IA-NEXT:    lb a0, 0(a0)
+; RV64IA-NEXT:    lbu a0, 0(a0)
 ; RV64IA-NEXT:    ret
   %1 = load atomic i8, ptr %a unordered, align 1
   ret i8 %1
@@ -71,7 +71,7 @@ define i8 @atomic_load_i8_monotonic(ptr %a) nounwind {
 ;
 ; RV32IA-LABEL: atomic_load_i8_monotonic:
 ; RV32IA:       # %bb.0:
-; RV32IA-NEXT:    lb a0, 0(a0)
+; RV32IA-NEXT:    lbu a0, 0(a0)
 ; RV32IA-NEXT:    ret
 ;
 ; RV64I-LABEL: atomic_load_i8_monotonic:
@@ -86,7 +86,7 @@ define i8 @atomic_load_i8_monotonic(ptr %a) nounwind {
 ;
 ; RV64IA-LABEL: atomic_load_i8_monotonic:
 ; RV64IA:       # %bb.0:
-; RV64IA-NEXT:    lb a0, 0(a0)
+; RV64IA-NEXT:    lbu a0, 0(a0)
 ; RV64IA-NEXT:    ret
   %1 = load atomic i8, ptr %a monotonic, align 1
   ret i8 %1
@@ -105,13 +105,13 @@ define i8 @atomic_load_i8_acquire(ptr %a) nounwind {
 ;
 ; RV32IA-WMO-LABEL: atomic_load_i8_acquire:
 ; RV32IA-WMO:       # %bb.0:
-; RV32IA-WMO-NEXT:    lb a0, 0(a0)
+; RV32IA-WMO-NEXT:    lbu a0, 0(a0)
 ; RV32IA-WMO-NEXT:    fence r, rw
 ; RV32IA-WMO-NEXT:    ret
 ;
 ; RV32IA-TSO-LABEL: atomic_load_i8_acquire:
 ; RV32IA-TSO:       # %bb.0:
-; RV32IA-TSO-NEXT:    lb a0, 0(a0)
+; RV32IA-TSO-NEXT:    lbu a0, 0(a0)
 ; RV32IA-TSO-NEXT:    ret
 ;
 ; RV64I-LABEL: atomic_load_i8_acquire:
@@ -126,35 +126,35 @@ define i8 @atomic_load_i8_acquire(ptr %a) nounwind {
 ;
 ; RV64IA-WMO-LABEL: atomic_load_i8_acquire:
 ; RV64IA-WMO:       # %bb.0:
-; RV64IA-WMO-NEXT:    lb a0, 0(a0)
+; RV64IA-WMO-NEXT:    lbu a0, 0(a0)
 ; RV64IA-WMO-NEXT:    fence r, rw
 ; RV64IA-WMO-NEXT:    ret
 ;
 ; RV64IA-TSO-LABEL: atomic_load_i8_acquire:
 ; RV64IA-TSO:       # %bb.0:
-; RV64IA-TSO-NEXT:    lb a0, 0(a0)
+; RV64IA-TSO-NEXT:    lbu a0, 0(a0)
 ; RV64IA-TSO-NEXT:    ret
 ;
 ; RV32IA-WMO-TRAILING-FENCE-LABEL: atomic_load_i8_acquire:
 ; RV32IA-WMO-TRAILING-FENCE:       # %bb.0:
-; RV32IA-WMO-TRAILING-FENCE-NEXT:    lb a0, 0(a0)
+; RV32IA-WMO-TRAILING-FENCE-NEXT:    lbu a0, 0(a0)
 ; RV32IA-WMO-TRAILING-FENCE-NEXT:    fence r, rw
 ; RV32IA-WMO-TRAILING-FENCE-NEXT:    ret
 ;
 ; RV32IA-TSO-TRAILING-FENCE-LABEL: atomic_load_i8_acquire:
 ; RV32IA-TSO-TRAILING-FENCE:       # %bb.0:
-; RV32IA-TSO-TRAILING-FENCE-NEXT:    lb a0, 0(a0)
+; RV32IA-TSO-TRAILING-FENCE-NEXT:    lbu a0, 0(a0)
 ; RV32IA-TSO-TRAILING-FENCE-NEXT:    ret
 ;
 ; RV64IA-WMO-TRAILING-FENCE-LABEL: atomic_load_i8_acquire:
 ; RV64IA-WMO-TRAILING-FENCE:       # %bb.0:
-; RV64IA-WMO-TRAILING-FENCE-NEXT:    lb a0, 0(a0)
+; RV64IA-WMO-TRAILING-FENCE-NEXT:    lbu a0, 0(a0)
 ; RV64IA-WMO-TRAILING-FENCE-NEXT:    fence r, rw
 ; RV64IA-WMO-TRAILING-FENCE-NEXT:    ret
 ;
 ; RV64IA-TSO-TRAILING-FENCE-LABEL: atomic_load_i8_acquire:
 ; RV64IA-TSO-TRAILING-FENCE:       # %bb.0:
-; RV64IA-TSO-TRAILING-FENCE-NEXT:    lb a0, 0(a0)
+; RV64IA-TSO-TRAILING-FENCE-NEXT:    lbu a0, 0(a0)
 ; RV64IA-TSO-TRAILING-FENCE-NEXT:    ret
   %1 = load atomic i8, ptr %a acquire, align 1
   ret i8 %1
@@ -174,14 +174,14 @@ define i8 @atomic_load_i8_seq_cst(ptr %a) nounwind {
 ; RV32IA-WMO-LABEL: atomic_load_i8_seq_cst:
 ; RV32IA-WMO:       # %bb.0:
 ; RV32IA-WMO-NEXT:    fence rw, rw
-; RV32IA-WMO-NEXT:    lb a0, 0(a0)
+; RV32IA-WMO-NEXT:    lbu a0, 0(a0)
 ; RV32IA-WMO-NEXT:    fence r, rw
 ; RV32IA-WMO-NEXT:    ret
 ;
 ; RV32IA-TSO-LABEL: atomic_load_i8_seq_cst:
 ; RV32IA-TSO:       # %bb.0:
 ; RV32IA-TSO-NEXT:    fence rw, rw
-; RV32IA-TSO-NEXT:    lb a0, 0(a0)
+; RV32IA-TSO-NEXT:    lbu a0, 0(a0)
 ; RV32IA-TSO-NEXT:    ret
 ;
 ; RV64I-LABEL: atomic_load_i8_seq_cst:
@@ -197,40 +197,40 @@ define i8 @atomic_load_i8_seq_cst(ptr %a) nounwind {
 ; RV64IA-WMO-LABEL: atomic_load_i8_seq_cst:
 ; RV64IA-WMO:       # %bb.0:
 ; RV64IA-WMO-NEXT:    fence rw, rw
-; RV64IA-WMO-NEXT:    lb a0, 0(a0)
+; RV64IA-WMO-NEXT:    lbu a0, 0(a0)
 ; RV64IA-WMO-NEXT:    fence r, rw
 ; RV64IA-WMO-NEXT:    ret
 ;
 ; RV64IA-TSO-LABEL: atomic_load_i8_seq_cst:
 ; RV64IA-TSO:       # %bb.0:
 ; RV64IA-TSO-NEXT:    fence rw, rw
-; RV64IA-TSO-NEXT:    lb a0, 0(a0)
+; RV64IA-TSO-NEXT:    lbu a0, 0(a0)
 ; RV64IA-TSO-NEXT:    ret
 ;
 ; RV32IA-WMO-TRAILING-FENCE-LABEL: atomic_load_i8_seq_cst:
 ; RV32IA-WMO-TRAILING-FENCE:       # %bb.0:
 ; RV32IA-WMO-TRAILING-FENCE-NEXT:    fence rw, rw
-; RV32IA-WMO-TRAILING-FENCE-NEXT:    lb a0, 0(a0)
+; RV32IA-WMO-TRAILING-FENCE-NEXT:    lbu a0, 0(a0)
 ; RV32IA-WMO-TRAILING-FENCE-NEXT:    fence r, rw
 ; RV32IA-WMO-TRAILING-FENCE-NEXT:    ret
 ;
 ; RV32IA-TSO-TRAILING-FENCE-LABEL: atomic_load_i8_seq_cst:
 ; RV32IA-TSO-TRAILING-FENCE:       # %bb.0:
 ; RV32IA-TSO-TRAILING-FENCE-NEXT:    fence rw, rw
-; RV32IA-TSO-TRAILING-FENCE-NEXT:    lb a0, 0(a0)
+; RV32IA-TSO-TRAILING-FENCE-NEXT:    lbu a0, 0(a0)
 ; RV32IA-TSO-TRAILING-FENCE-NEXT:    ret
 ;
 ; RV64IA-WMO-TRAILING-FENCE-LABEL: atomic_load_i8_seq_cst:
 ; RV64IA-WMO-TRAILING-FENCE:       # %bb.0:
 ; RV64IA-WMO-TRAILING-FENCE-NEXT:    fence rw, rw
-; RV64IA-WMO-TRAILING-FENCE-NEXT:    lb a0, 0(a0)
+; RV64IA-WMO-TRAILING-FENCE-NEXT:    lbu a0, 0(a0)
 ; RV64IA-WMO-TRAILING-FENCE-NEXT:    fence r, rw
 ; RV64IA-WMO-TRAILING-FENCE-NEXT:    ret
 ;
 ; RV64IA-TSO-TRAILING-FENCE-LABEL: atomic_load_i8_seq_cst:
 ; RV64IA-TSO-TRAILING-FENCE:       # %bb.0:
 ; RV64IA-TSO-TRAILING-FENCE-NEXT:    fence rw, rw
-; RV64IA-TSO-TRAILING-FENCE-NEXT:    lb a0, 0(a0)
+; RV64IA-TSO-TRAILING-FENCE-NEXT:    lbu a0, 0(a0)
 ; RV64IA-TSO-TRAILING-FENCE-NEXT:    ret
   %1 = load atomic i8, ptr %a seq_cst, align 1
   ret i8 %1
