[llvm] [RISCV] Prefer QC_EXTU to ANDI for certain 12-bit mask immediates (PR #143838)

[via llvm-commits]

llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

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

Author: Sudharsan Veeravalli (svs-quic)

<details>
<summary>Changes</summary>

QC_EXTU can be compressed to QC_C_EXTU when the immediate is a mask >=63. We currently only handle masks that don't fit in 12-bits in RISCVISelDAGToDAG. 

I have added patterns than changing code in RISCVISelDAGToDAG since the other extract instructions don't have compressed versions and it is a lot easier to maintain things this way.

---
Full diff: https://github.com/llvm/llvm-project/pull/143838.diff


2 Files Affected:

- (modified) llvm/lib/Target/RISCV/RISCVInstrInfoXqci.td (+8) 
- (modified) llvm/test/CodeGen/RISCV/xqcibm-extract.ll (+42) 


``````````diff
diff --git a/llvm/lib/Target/RISCV/RISCVInstrInfoXqci.td b/llvm/lib/Target/RISCV/RISCVInstrInfoXqci.td
index dba035bab928c..9f96a3ed80561 100644
--- a/llvm/lib/Target/RISCV/RISCVInstrInfoXqci.td
+++ b/llvm/lib/Target/RISCV/RISCVInstrInfoXqci.td
@@ -1441,6 +1441,14 @@ let Predicates = [HasVendorXqcibm, IsRV32] in {
 def : Pat<(sext_inreg (i32 GPR:$rs1), i16), (QC_EXT GPR:$rs1, 16, 0)>;
 def : Pat<(sext_inreg (i32 GPR:$rs1), i8), (QC_EXT GPR:$rs1, 8, 0)>;
 def : Pat<(sext_inreg (i32 GPR:$rs1), i1), (QC_EXT GPR:$rs1, 1, 0)>;
+
+// Prefer qc.extu to andi for the following cases since the former can be compressed
+def : Pat<(i32 (and GPRNoX0:$rs, 63)), (QC_EXTU GPRNoX0:$rs, 6, 0)>;
+def : Pat<(i32 (and GPRNoX0:$rs, 127)), (QC_EXTU GPRNoX0:$rs, 7, 0)>;
+def : Pat<(i32 (and GPRNoX0:$rs, 255)), (QC_EXTU GPRNoX0:$rs, 8, 0)>;
+def : Pat<(i32 (and GPRNoX0:$rs, 511)), (QC_EXTU GPRNoX0:$rs, 9, 0)>;
+def : Pat<(i32 (and GPRNoX0:$rs, 1023)), (QC_EXTU GPRNoX0:$rs, 10, 0)>;
+def : Pat<(i32 (and GPRNoX0:$rs, 2047)), (QC_EXTU GPRNoX0:$rs, 11, 0)>;
 } // Predicates = [HasVendorXqcibm, IsRV32]
 
 let Predicates = [HasVendorXqciint, IsRV32] in
diff --git a/llvm/test/CodeGen/RISCV/xqcibm-extract.ll b/llvm/test/CodeGen/RISCV/xqcibm-extract.ll
index cb01510058da4..edf6e9a2d5019 100644
--- a/llvm/test/CodeGen/RISCV/xqcibm-extract.ll
+++ b/llvm/test/CodeGen/RISCV/xqcibm-extract.ll
@@ -247,6 +247,48 @@ define i32 @extu_from_and_i32(i32 %x) {
   ret i32 %a
 }
 
+define i32 @no_extu_from_and_i32(i32 %x) {
+; RV32I-LABEL: no_extu_from_and_i32:
+; RV32I:       # %bb.0:
+; RV32I-NEXT:    andi a0, a0, 31
+; RV32I-NEXT:    ret
+;
+; RV32XQCIBM-LABEL: no_extu_from_and_i32:
+; RV32XQCIBM:       # %bb.0:
+; RV32XQCIBM-NEXT:    andi a0, a0, 31
+; RV32XQCIBM-NEXT:    ret
+  %a = and i32 %x, 31
+  ret i32 %a
+}
+
+define i32 @extu_from_and_i32_simm12_lb(i32 %x) {
+; RV32I-LABEL: extu_from_and_i32_simm12_lb:
+; RV32I:       # %bb.0:
+; RV32I-NEXT:    andi a0, a0, 63
+; RV32I-NEXT:    ret
+;
+; RV32XQCIBM-LABEL: extu_from_and_i32_simm12_lb:
+; RV32XQCIBM:       # %bb.0:
+; RV32XQCIBM-NEXT:    qc.extu a0, a0, 6, 0
+; RV32XQCIBM-NEXT:    ret
+  %a = and i32 %x, 63
+  ret i32 %a
+}
+
+define i32 @extu_from_and_i32_simm12_ub(i32 %x) {
+; RV32I-LABEL: extu_from_and_i32_simm12_ub:
+; RV32I:       # %bb.0:
+; RV32I-NEXT:    andi a0, a0, 2047
+; RV32I-NEXT:    ret
+;
+; RV32XQCIBM-LABEL: extu_from_and_i32_simm12_ub:
+; RV32XQCIBM:       # %bb.0:
+; RV32XQCIBM-NEXT:    qc.extu a0, a0, 11, 0
+; RV32XQCIBM-NEXT:    ret
+  %a = and i32 %x, 2047
+  ret i32 %a
+}
+
 define i64 @extu_from_and_i64(i64 %x) {
 ; RV32I-LABEL: extu_from_and_i64:
 ; RV32I:       # %bb.0:

``````````

</details>


https://github.com/llvm/llvm-project/pull/143838