[llvm] [DAGCombiner] Fold subtraction if above a constant threshold to `umin` (PR #135194)

[Craig Topper via llvm-commits]

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@@ -1720,45 +1720,67 @@ define i32 @sub_if_uge_multiuse_cmp_store_i32(i32 %x, i32 %y, ptr %z) {
 }
 
 define i8 @sub_if_uge_C_i8(i8 zeroext %x) {
-; CHECK-LABEL: sub_if_uge_C_i8:
-; CHECK:       # %bb.0:
-; CHECK-NEXT:    sltiu a1, a0, 13
-; CHECK-NEXT:    addi a1, a1, -1
-; CHECK-NEXT:    andi a1, a1, -13
-; CHECK-NEXT:    add a0, a0, a1
-; CHECK-NEXT:    ret
+; RV32I-LABEL: sub_if_uge_C_i8:
+; RV32I:       # %bb.0:
+; RV32I-NEXT:    sltiu a1, a0, 13
+; RV32I-NEXT:    addi a1, a1, -1
+; RV32I-NEXT:    andi a1, a1, -13
+; RV32I-NEXT:    add a0, a0, a1
+; RV32I-NEXT:    ret
+;
+; RV32ZBB-LABEL: sub_if_uge_C_i8:
+; RV32ZBB:       # %bb.0:
+; RV32ZBB-NEXT:    addi a1, a0, -13
+; RV32ZBB-NEXT:    zext.b a1, a1
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topperc wrote:

I think you'll probably need a new DAGCombine for it.

https://github.com/llvm/llvm-project/pull/135194