[llvm] [RISCV] Optimize `(and (i1) f, (setcc a, b, eq))` to use the zicond extension (PR #217946)
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Fri Aug 21 11:25:44 PDT 2026
llvmorg-github-actions[bot] wrote:
<!--LLVM PR SUMMARY COMMENT-->
@llvm/pr-subscribers-backend-risc-v
Author: Afonso Bordado (afonso360)
<details>
<summary>Changes</summary>
This is a generalization of the previously existing rule, that required one of the sides of the `setcc` to be zero.
With this commit we now support comparisons between any two variables. This requires us to insert an additional instruction to compare the two. But it is still beneficial vs the unoptimized lowering as it reduces 1 instruction in the output.
This fixes one of the issues identified in #<!-- -->179584. Namely `test_lt3`, now uses `czero.{nez,eqz}` for those cases.
---
Full diff: https://github.com/llvm/llvm-project/pull/217946.diff
2 Files Affected:
- (modified) llvm/lib/Target/RISCV/RISCVISelLowering.cpp (+23-7)
- (modified) llvm/test/CodeGen/RISCV/zicond-opts.ll (+124-8)
``````````diff
diff --git a/llvm/lib/Target/RISCV/RISCVISelLowering.cpp b/llvm/lib/Target/RISCV/RISCVISelLowering.cpp
index 5bd12f635ac76..309010d2c0424 100644
--- a/llvm/lib/Target/RISCV/RISCVISelLowering.cpp
+++ b/llvm/lib/Target/RISCV/RISCVISelLowering.cpp
@@ -18272,6 +18272,11 @@ static SDValue reverseZExtICmpCombine(SDNode *N, SelectionDAG &DAG,
return DAG.getNode(ISD::ZERO_EXTEND, DL, VT, Res);
}
+// (and (i1) f, (setcc a, b, eq)) -> (czero.nez f, (xor a, b))
+// (and (i1) f, (setcc a, b, ne)) -> (czero.eqz f, (xor a, b))
+// (and (setcc a, b, eq), (i1) g) -> (czero.nez g, (xor a, b))
+// (and (setcc a, b, ne), (i1) g) -> (czero.eqz g, (xor a, b))
+//
// (and (i1) f, (setcc c, 0, ne)) -> (czero.nez f, c)
// (and (i1) f, (setcc c, 0, eq)) -> (czero.eqz f, c)
// (and (setcc c, 0, ne), (i1) g) -> (czero.nez g, c)
@@ -18284,8 +18289,8 @@ static SDValue combineANDOfSETCCToCZERO(SDNode *N, SelectionDAG &DAG,
SDValue N0 = N->getOperand(0);
SDValue N1 = N->getOperand(1);
- auto IsEqualCompZero = [](SDValue &V) -> bool {
- if (V.getOpcode() == ISD::SETCC && isNullConstant(V.getOperand(1))) {
+ auto IsSetCCEquality = [](SDValue &V) -> bool {
+ if (V.getOpcode() == ISD::SETCC) {
ISD::CondCode CC = cast<CondCodeSDNode>(V.getOperand(2))->get();
if (ISD::isIntEqualitySetCC(CC))
return true;
@@ -18293,23 +18298,34 @@ static SDValue combineANDOfSETCCToCZERO(SDNode *N, SelectionDAG &DAG,
return false;
};
- if (!IsEqualCompZero(N0) || !N0.hasOneUse())
+ if (!IsSetCCEquality(N0) || !N0.hasOneUse())
std::swap(N0, N1);
- if (!IsEqualCompZero(N0) || !N0.hasOneUse())
+ if (!IsSetCCEquality(N0) || !N0.hasOneUse())
return SDValue();
KnownBits Known = DAG.computeKnownBits(N1);
if (Known.getMaxValue().ugt(1))
return SDValue();
+ SDLoc DL(N);
+ EVT VT = N->getValueType(0);
unsigned CzeroOpcode =
(cast<CondCodeSDNode>(N0.getOperand(2))->get() == ISD::SETNE)
? RISCVISD::CZERO_EQZ
: RISCVISD::CZERO_NEZ;
- EVT VT = N->getValueType(0);
- SDLoc DL(N);
- return DAG.getNode(CzeroOpcode, DL, VT, N1, N0.getOperand(0));
+ // From here we have two cases:
+ // Either setcc is a comparision with zero, and we can lower directly to a
+ // czero instruction; Or it's not a constant zero, in which case we can still
+ // use a czero, but we first need to get a zero or one value comparing the two
+ // sides of setcc.
+ SDValue Rhs = N0.getOperand(0);
+ if (!isNullConstant(N0->getOperand(1))) {
+ Rhs = DAG.getNode(ISD::XOR, DL, N0.getValueType(), N0.getOperand(0),
+ N0.getOperand(1));
+ }
+
+ return DAG.getNode(CzeroOpcode, DL, VT, N1, Rhs);
}
static SDValue reduceANDOfAtomicLoad(SDNode *N,
diff --git a/llvm/test/CodeGen/RISCV/zicond-opts.ll b/llvm/test/CodeGen/RISCV/zicond-opts.ll
index e6b36537b2b90..34e4da410ed79 100644
--- a/llvm/test/CodeGen/RISCV/zicond-opts.ll
+++ b/llvm/test/CodeGen/RISCV/zicond-opts.ll
@@ -163,6 +163,122 @@ define i32 @icmp_and_and(i64 %x, i64 %y, i64 %z) {
ret i32 %9
}
+; (and (i1) f, (setcc a, b, eq)) -> (czero.nez f, (xor a, b))
+define i1 @and_icmp_eq_non_constant(i64 %x0, i64 %x1, i64 %y0, i64 %y1) {
+; RV32ZICOND-LABEL: and_icmp_eq_non_constant:
+; RV32ZICOND: # %bb.0:
+; RV32ZICOND-NEXT: xor t0, a1, a5
+; RV32ZICOND-NEXT: sltu a0, a0, a4
+; RV32ZICOND-NEXT: czero.nez a0, a0, t0
+; RV32ZICOND-NEXT: sltu a1, a1, a5
+; RV32ZICOND-NEXT: or a0, a0, a1
+; RV32ZICOND-NEXT: xor a1, a3, a7
+; RV32ZICOND-NEXT: xor a4, a2, a6
+; RV32ZICOND-NEXT: or a4, a4, a1
+; RV32ZICOND-NEXT: sltu a2, a2, a6
+; RV32ZICOND-NEXT: czero.nez a1, a2, a1
+; RV32ZICOND-NEXT: sltu a2, a3, a7
+; RV32ZICOND-NEXT: czero.nez a0, a0, a4
+; RV32ZICOND-NEXT: or a1, a1, a2
+; RV32ZICOND-NEXT: or a0, a1, a0
+; RV32ZICOND-NEXT: ret
+;
+; RV64ZICOND-LABEL: and_icmp_eq_non_constant:
+; RV64ZICOND: # %bb.0:
+; RV64ZICOND-NEXT: sltu a0, a0, a2
+; RV64ZICOND-NEXT: xor a2, a1, a3
+; RV64ZICOND-NEXT: czero.nez a0, a0, a2
+; RV64ZICOND-NEXT: sltu a1, a1, a3
+; RV64ZICOND-NEXT: or a0, a1, a0
+; RV64ZICOND-NEXT: ret
+
+ %5 = icmp ult i64 %x0, %y0
+ %6 = icmp eq i64 %x1, %y1
+ %7 = and i1 %5, %6
+ %8 = icmp ult i64 %x1, %y1
+ %9 = or i1 %8, %7
+ ret i1 %9
+}
+
+; (and (i1) f, (setcc a, b, ne)) -> (czero.eqz f, (xor a, b))
+define i1 @and_icmp_ne_non_constant(i64 %x0, i64 %x1, i64 %y0, i64 %y1) {
+; RV32ZICOND-LABEL: and_icmp_ne_non_constant:
+; RV32ZICOND: # %bb.0:
+; RV32ZICOND-NEXT: xor t0, a1, a5
+; RV32ZICOND-NEXT: sltu a0, a0, a4
+; RV32ZICOND-NEXT: czero.nez a0, a0, t0
+; RV32ZICOND-NEXT: sltu a1, a1, a5
+; RV32ZICOND-NEXT: or a0, a0, a1
+; RV32ZICOND-NEXT: xor a1, a3, a7
+; RV32ZICOND-NEXT: xor a4, a2, a6
+; RV32ZICOND-NEXT: or a4, a4, a1
+; RV32ZICOND-NEXT: sltu a2, a2, a6
+; RV32ZICOND-NEXT: czero.nez a1, a2, a1
+; RV32ZICOND-NEXT: sltu a2, a3, a7
+; RV32ZICOND-NEXT: czero.eqz a0, a0, a4
+; RV32ZICOND-NEXT: or a1, a1, a2
+; RV32ZICOND-NEXT: or a0, a1, a0
+; RV32ZICOND-NEXT: ret
+;
+; RV64ZICOND-LABEL: and_icmp_ne_non_constant:
+; RV64ZICOND: # %bb.0:
+; RV64ZICOND-NEXT: sltu a0, a0, a2
+; RV64ZICOND-NEXT: xor a2, a1, a3
+; RV64ZICOND-NEXT: czero.eqz a0, a0, a2
+; RV64ZICOND-NEXT: sltu a1, a1, a3
+; RV64ZICOND-NEXT: or a0, a1, a0
+; RV64ZICOND-NEXT: ret
+
+ %5 = icmp ult i64 %x0, %y0
+ %6 = icmp ne i64 %x1, %y1
+ %7 = and i1 %5, %6
+ %8 = icmp ult i64 %x1, %y1
+ %9 = or i1 %8, %7
+ ret i1 %9
+}
+
+; (and (i1) f, (setcc a, b, ne)) -> (czero.eqz f, (xor a, b))
+; Test the above transform, but setcc has multiple uses, so we can't transform.
+define i32 @and_icmp_eq_non_constant_multiple_uses(i64 %x0, i64 %x1, i64 %y0, i64 %y1) {
+; RV32ZICOND-LABEL: and_icmp_eq_non_constant_multiple_uses:
+; RV32ZICOND: # %bb.0:
+; RV32ZICOND-NEXT: xor t0, a1, a5
+; RV32ZICOND-NEXT: sltu a0, a0, a4
+; RV32ZICOND-NEXT: czero.nez a0, a0, t0
+; RV32ZICOND-NEXT: xor a3, a3, a7
+; RV32ZICOND-NEXT: xor a2, a2, a6
+; RV32ZICOND-NEXT: sltu a1, a1, a5
+; RV32ZICOND-NEXT: or a2, a2, a3
+; RV32ZICOND-NEXT: or a0, a0, a1
+; RV32ZICOND-NEXT: seqz a1, a2
+; RV32ZICOND-NEXT: and a0, a0, a1
+; RV32ZICOND-NEXT: add a0, a0, a1
+; RV32ZICOND-NEXT: ret
+;
+; RV64ZICOND-LABEL: and_icmp_eq_non_constant_multiple_uses:
+; RV64ZICOND: # %bb.0:
+; RV64ZICOND-NEXT: xor a1, a1, a3
+; RV64ZICOND-NEXT: sltu a0, a0, a2
+; RV64ZICOND-NEXT: seqz a1, a1
+; RV64ZICOND-NEXT: and a0, a0, a1
+; RV64ZICOND-NEXT: add a0, a0, a1
+; RV64ZICOND-NEXT: ret
+
+ %lt = icmp ult i64 %x0, %y0
+ %eq = icmp eq i64 %x1, %y1
+
+ ; First use of %eq.
+ %both = and i1 %lt, %eq
+
+ %both.ext = zext i1 %both to i32
+
+ ; Second use of %eq.
+ %eq.ext = zext i1 %eq to i32
+
+ %result = add i32 %both.ext, %eq.ext
+ ret i32 %result
+}
+
; (select cond, x, rotl(x, rot.amt)) -> (rotl x, (czero_nez rot.amt, cond))
define i64 @rotate_l_nez(i64 %x, i64 %rot.amt, i1 %cond) {
; RV32ZICOND-LABEL: rotate_l_nez:
@@ -426,19 +542,19 @@ define i64 @select_wo_optsize_minsize(i64 %true, i64 %false, i1 zeroext %c) {
define i64 @select_w_optsize(i64 %true, i64 %false, i1 zeroext %c) optsize {
; RV32ZICOND-LABEL: select_w_optsize:
; RV32ZICOND: # %bb.0:
-; RV32ZICOND-NEXT: bnez a4, .LBB16_2
+; RV32ZICOND-NEXT: bnez a4, .LBB19_2
; RV32ZICOND-NEXT: # %bb.1:
; RV32ZICOND-NEXT: mv a0, a2
; RV32ZICOND-NEXT: mv a1, a3
-; RV32ZICOND-NEXT: .LBB16_2:
+; RV32ZICOND-NEXT: .LBB19_2:
; RV32ZICOND-NEXT: ret
;
; RV64ZICOND-LABEL: select_w_optsize:
; RV64ZICOND: # %bb.0:
-; RV64ZICOND-NEXT: bnez a2, .LBB16_2
+; RV64ZICOND-NEXT: bnez a2, .LBB19_2
; RV64ZICOND-NEXT: # %bb.1:
; RV64ZICOND-NEXT: mv a0, a1
-; RV64ZICOND-NEXT: .LBB16_2:
+; RV64ZICOND-NEXT: .LBB19_2:
; RV64ZICOND-NEXT: ret
%r = select i1 %c, i64 %true, i64 %false
ret i64 %r
@@ -447,19 +563,19 @@ define i64 @select_w_optsize(i64 %true, i64 %false, i1 zeroext %c) optsize {
define i64 @select_w_minsize(i64 %true, i64 %false, i1 zeroext %c) minsize {
; RV32ZICOND-LABEL: select_w_minsize:
; RV32ZICOND: # %bb.0:
-; RV32ZICOND-NEXT: bnez a4, .LBB17_2
+; RV32ZICOND-NEXT: bnez a4, .LBB20_2
; RV32ZICOND-NEXT: # %bb.1:
; RV32ZICOND-NEXT: mv a0, a2
; RV32ZICOND-NEXT: mv a1, a3
-; RV32ZICOND-NEXT: .LBB17_2:
+; RV32ZICOND-NEXT: .LBB20_2:
; RV32ZICOND-NEXT: ret
;
; RV64ZICOND-LABEL: select_w_minsize:
; RV64ZICOND: # %bb.0:
-; RV64ZICOND-NEXT: bnez a2, .LBB17_2
+; RV64ZICOND-NEXT: bnez a2, .LBB20_2
; RV64ZICOND-NEXT: # %bb.1:
; RV64ZICOND-NEXT: mv a0, a1
-; RV64ZICOND-NEXT: .LBB17_2:
+; RV64ZICOND-NEXT: .LBB20_2:
; RV64ZICOND-NEXT: ret
%r = select i1 %c, i64 %true, i64 %false
ret i64 %r
``````````
</details>
https://github.com/llvm/llvm-project/pull/217946
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