[llvm] [RISCV] Fold subtraction if above threshold to Zbb `minu` (PR #134235)

[Luke Lau via llvm-commits]

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@@ -1525,101 +1531,187 @@ define i16 @sub_if_uge_i16(i16 %x, i16 %y) {
 }
 
 define i32 @sub_if_uge_i32(i32 %x, i32 %y) {
-; CHECK-LABEL: sub_if_uge_i32:
-; CHECK:       # %bb.0:
-; CHECK-NEXT:    sltu a2, a0, a1
-; CHECK-NEXT:    addi a2, a2, -1
-; CHECK-NEXT:    and a1, a2, a1
-; CHECK-NEXT:    sub a0, a0, a1
-; CHECK-NEXT:    ret
+; RV32I-LABEL: sub_if_uge_i32:
+; RV32I:       # %bb.0:
+; RV32I-NEXT:    sltu a2, a0, a1
+; RV32I-NEXT:    addi a2, a2, -1
+; RV32I-NEXT:    and a1, a2, a1
+; RV32I-NEXT:    sub a0, a0, a1
+; RV32I-NEXT:    ret
+;
+; RV32ZBB-LABEL: sub_if_uge_i32:
+; RV32ZBB:       # %bb.0:
+; RV32ZBB-NEXT:    sub a1, a0, a1
+; RV32ZBB-NEXT:    minu a0, a0, a1
+; RV32ZBB-NEXT:    ret
   %cmp = icmp ult i32 %x, %y
   %select = select i1 %cmp, i32 0, i32 %y
   %sub = sub nuw i32 %x, %select
   ret i32 %sub
 }
 
 define i64 @sub_if_uge_i64(i64 %x, i64 %y) {
-; CHECK-LABEL: sub_if_uge_i64:
-; CHECK:       # %bb.0:
-; CHECK-NEXT:    beq a1, a3, .LBB52_2
-; CHECK-NEXT:  # %bb.1:
-; CHECK-NEXT:    sltu a4, a1, a3
-; CHECK-NEXT:    j .LBB52_3
-; CHECK-NEXT:  .LBB52_2:
-; CHECK-NEXT:    sltu a4, a0, a2
-; CHECK-NEXT:  .LBB52_3:
-; CHECK-NEXT:    addi a4, a4, -1
-; CHECK-NEXT:    and a3, a4, a3
-; CHECK-NEXT:    and a2, a4, a2
-; CHECK-NEXT:    sltu a4, a0, a2
-; CHECK-NEXT:    sub a1, a1, a3
-; CHECK-NEXT:    sub a1, a1, a4
-; CHECK-NEXT:    sub a0, a0, a2
-; CHECK-NEXT:    ret
+; RV32I-LABEL: sub_if_uge_i64:
+; RV32I:       # %bb.0:
+; RV32I-NEXT:    beq a1, a3, .LBB52_2
+; RV32I-NEXT:  # %bb.1:
+; RV32I-NEXT:    sltu a4, a1, a3
+; RV32I-NEXT:    j .LBB52_3
+; RV32I-NEXT:  .LBB52_2:
+; RV32I-NEXT:    sltu a4, a0, a2
+; RV32I-NEXT:  .LBB52_3:
+; RV32I-NEXT:    addi a4, a4, -1
+; RV32I-NEXT:    and a3, a4, a3
+; RV32I-NEXT:    and a2, a4, a2
+; RV32I-NEXT:    sltu a4, a0, a2
+; RV32I-NEXT:    sub a1, a1, a3
+; RV32I-NEXT:    sub a1, a1, a4
+; RV32I-NEXT:    sub a0, a0, a2
+; RV32I-NEXT:    ret
+;
+; RV32ZBB-LABEL: sub_if_uge_i64:
----------------
lukel97 wrote:

You might also need to call TLI.getTypeToTransformTo for i8 + i16

https://github.com/llvm/llvm-project/pull/134235