[llvm] [PowerPC] Add custom lowering for SADD overflow for i32 and i64 (PR #159255)
Aditi Medhane via llvm-commits
llvm-commits at lists.llvm.org
Mon Nov 17 00:07:35 PST 2025
https://github.com/AditiRM updated https://github.com/llvm/llvm-project/pull/159255
>From 8e3f617fbc22b0733cf9b3b0415aba6fe6b700da Mon Sep 17 00:00:00 2001
From: AditiRM <aditimedhane73 at gmail.com>
Date: Wed, 17 Sep 2025 06:54:02 +0000
Subject: [PATCH 1/4] [PowerPC] Add custom lowering for SADD overflow for i32
and i64
---
llvm/lib/Target/PowerPC/PPCISelLowering.cpp | 32 ++++++++++++++++++++-
llvm/lib/Target/PowerPC/PPCISelLowering.h | 1 +
llvm/test/CodeGen/PowerPC/saddo-ssubo.ll | 22 +++++++-------
3 files changed, 42 insertions(+), 13 deletions(-)
diff --git a/llvm/lib/Target/PowerPC/PPCISelLowering.cpp b/llvm/lib/Target/PowerPC/PPCISelLowering.cpp
index fa104e4f69d7f..0798dae3a14a2 100644
--- a/llvm/lib/Target/PowerPC/PPCISelLowering.cpp
+++ b/llvm/lib/Target/PowerPC/PPCISelLowering.cpp
@@ -204,8 +204,11 @@ PPCTargetLowering::PPCTargetLowering(const PPCTargetMachine &TM,
// setbc instruction.
if (!Subtarget.hasP10Vector()) {
setOperationAction(ISD::SSUBO, MVT::i32, Custom);
- if (isPPC64)
+ setOperationAction(ISD::SADDO, MVT::i32, Custom);
+ if (isPPC64){
setOperationAction(ISD::SSUBO, MVT::i64, Custom);
+ setOperationAction(ISD::SADDO, MVT::i64, Custom);
+ }
}
// Match BITREVERSE to customized fast code sequence in the td file.
@@ -12614,6 +12617,31 @@ SDValue PPCTargetLowering::LowerSSUBO(SDValue Op, SelectionDAG &DAG) const {
return DAG.getMergeValues({Sub, OverflowTrunc}, dl);
}
+SDValue PPCTargetLowering::LowerSADDO(SDValue Op, SelectionDAG &DAG) const {
+
+ SDLoc dl(Op);
+ SDValue LHS = Op.getOperand(0);
+ SDValue RHS = Op.getOperand(1);
+ EVT VT = Op.getNode()->getValueType(0);
+
+ SDValue Add = DAG.getNode(ISD::ADD, dl, VT, LHS, RHS);
+
+ SDValue Xor1 = DAG.getNode(ISD::XOR, dl, VT, LHS, RHS);
+ SDValue NotXor1 = DAG.getNOT(dl, Xor1, VT);
+ SDValue Xor2 = DAG.getNode(ISD::XOR, dl, VT, Add, LHS);
+
+ SDValue And = DAG.getNode(ISD::AND, dl, VT, NotXor1, Xor2);
+
+ SDValue Overflow =
+ DAG.getNode(ISD::SRL, dl, VT, And,
+ DAG.getConstant(VT.getSizeInBits() - 1, dl, MVT::i32));
+
+ SDValue OverflowTrunc =
+ DAG.getNode(ISD::TRUNCATE, dl, Op.getNode()->getValueType(1), Overflow);
+
+ return DAG.getMergeValues({Add, OverflowTrunc}, dl);
+}
+
/// LowerOperation - Provide custom lowering hooks for some operations.
///
SDValue PPCTargetLowering::LowerOperation(SDValue Op, SelectionDAG &DAG) const {
@@ -12638,6 +12666,8 @@ SDValue PPCTargetLowering::LowerOperation(SDValue Op, SelectionDAG &DAG) const {
case ISD::ADJUST_TRAMPOLINE: return LowerADJUST_TRAMPOLINE(Op, DAG);
case ISD::SSUBO:
return LowerSSUBO(Op, DAG);
+ case ISD::SADDO:
+ return LowerSADDO(Op, DAG);
case ISD::INLINEASM:
case ISD::INLINEASM_BR: return LowerINLINEASM(Op, DAG);
diff --git a/llvm/lib/Target/PowerPC/PPCISelLowering.h b/llvm/lib/Target/PowerPC/PPCISelLowering.h
index 669430550f4e6..0c19632ab5b33 100644
--- a/llvm/lib/Target/PowerPC/PPCISelLowering.h
+++ b/llvm/lib/Target/PowerPC/PPCISelLowering.h
@@ -1283,6 +1283,7 @@ namespace llvm {
SDValue LowerJumpTable(SDValue Op, SelectionDAG &DAG) const;
SDValue LowerSETCC(SDValue Op, SelectionDAG &DAG) const;
SDValue LowerSSUBO(SDValue Op, SelectionDAG &DAG) const;
+ SDValue LowerSADDO(SDValue Op, SelectionDAG &DAG) const;
SDValue LowerINIT_TRAMPOLINE(SDValue Op, SelectionDAG &DAG) const;
SDValue LowerADJUST_TRAMPOLINE(SDValue Op, SelectionDAG &DAG) const;
SDValue LowerINLINEASM(SDValue Op, SelectionDAG &DAG) const;
diff --git a/llvm/test/CodeGen/PowerPC/saddo-ssubo.ll b/llvm/test/CodeGen/PowerPC/saddo-ssubo.ll
index c0f3b60122521..5cd96ec219404 100644
--- a/llvm/test/CodeGen/PowerPC/saddo-ssubo.ll
+++ b/llvm/test/CodeGen/PowerPC/saddo-ssubo.ll
@@ -49,12 +49,11 @@ entry:
define i1 @test_saddo_i32(i32 %a, i32 %b) nounwind {
; CHECK-LABEL: test_saddo_i32:
; CHECK: # %bb.0: # %entry
-; CHECK-NEXT: add 5, 3, 4
-; CHECK-NEXT: cmpwi 1, 4, 0
-; CHECK-NEXT: cmpw 5, 3
-; CHECK-NEXT: li 3, 1
-; CHECK-NEXT: creqv 20, 4, 0
-; CHECK-NEXT: isel 3, 0, 3, 20
+; CHECK-NEXT: xor 5, 3, 4
+; CHECK-NEXT: add 4, 3, 4
+; CHECK-NEXT: xor 3, 4, 3
+; CHECK-NEXT: andc 3, 3, 5
+; CHECK-NEXT: srwi 3, 3, 31
; CHECK-NEXT: blr
entry:
%res = call { i32, i1 } @llvm.sadd.with.overflow.i32(i32 %a, i32 %b) nounwind
@@ -65,12 +64,11 @@ entry:
define i1 @test_saddo_i64(i64 %a, i64 %b) nounwind {
; CHECK-LABEL: test_saddo_i64:
; CHECK: # %bb.0: # %entry
-; CHECK-NEXT: add 5, 3, 4
-; CHECK-NEXT: cmpdi 1, 4, 0
-; CHECK-NEXT: cmpd 5, 3
-; CHECK-NEXT: li 3, 1
-; CHECK-NEXT: creqv 20, 4, 0
-; CHECK-NEXT: isel 3, 0, 3, 20
+; CHECK-NEXT: xor 5, 3, 4
+; CHECK-NEXT: add 4, 3, 4
+; CHECK-NEXT: xor 3, 4, 3
+; CHECK-NEXT: andc 3, 3, 5
+; CHECK-NEXT: rldicl 3, 3, 1, 63
; CHECK-NEXT: blr
entry:
%res = call { i64, i1 } @llvm.sadd.with.overflow.i64(i64 %a, i64 %b) nounwind
>From f773eadf5a2a1ad2a7e32813e4201f1b36fb8c58 Mon Sep 17 00:00:00 2001
From: AditiRM <aditimedhane73 at gmail.com>
Date: Wed, 17 Sep 2025 07:08:15 +0000
Subject: [PATCH 2/4] [nit] fix formating
---
llvm/lib/Target/PowerPC/PPCISelLowering.cpp | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/llvm/lib/Target/PowerPC/PPCISelLowering.cpp b/llvm/lib/Target/PowerPC/PPCISelLowering.cpp
index 0798dae3a14a2..4e4e9a9ab8a74 100644
--- a/llvm/lib/Target/PowerPC/PPCISelLowering.cpp
+++ b/llvm/lib/Target/PowerPC/PPCISelLowering.cpp
@@ -205,7 +205,7 @@ PPCTargetLowering::PPCTargetLowering(const PPCTargetMachine &TM,
if (!Subtarget.hasP10Vector()) {
setOperationAction(ISD::SSUBO, MVT::i32, Custom);
setOperationAction(ISD::SADDO, MVT::i32, Custom);
- if (isPPC64){
+ if (isPPC64) {
setOperationAction(ISD::SSUBO, MVT::i64, Custom);
setOperationAction(ISD::SADDO, MVT::i64, Custom);
}
>From d02c711c5c253b3ab5230bad039dc06a473289bf Mon Sep 17 00:00:00 2001
From: AditiRM <aditimedhane73 at gmail.com>
Date: Mon, 17 Nov 2025 07:56:16 +0000
Subject: [PATCH 3/4] Review comments
---
llvm/lib/Target/PowerPC/PPCISelLowering.cpp | 24 +++++++++++++--------
1 file changed, 15 insertions(+), 9 deletions(-)
diff --git a/llvm/lib/Target/PowerPC/PPCISelLowering.cpp b/llvm/lib/Target/PowerPC/PPCISelLowering.cpp
index 4e4e9a9ab8a74..f4a8fa01d7ea5 100644
--- a/llvm/lib/Target/PowerPC/PPCISelLowering.cpp
+++ b/llvm/lib/Target/PowerPC/PPCISelLowering.cpp
@@ -12617,6 +12617,8 @@ SDValue PPCTargetLowering::LowerSSUBO(SDValue Op, SelectionDAG &DAG) const {
return DAG.getMergeValues({Sub, OverflowTrunc}, dl);
}
+/// Implements signed add with overflow detection using the rule:
+/// (x eqv y) & (sum xor x), where the overflow bit is extracted from the sign
SDValue PPCTargetLowering::LowerSADDO(SDValue Op, SelectionDAG &DAG) const {
SDLoc dl(Op);
@@ -12624,22 +12626,26 @@ SDValue PPCTargetLowering::LowerSADDO(SDValue Op, SelectionDAG &DAG) const {
SDValue RHS = Op.getOperand(1);
EVT VT = Op.getNode()->getValueType(0);
- SDValue Add = DAG.getNode(ISD::ADD, dl, VT, LHS, RHS);
+ SDValue Sum = DAG.getNode(ISD::ADD, dl, VT, LHS, RHS);
- SDValue Xor1 = DAG.getNode(ISD::XOR, dl, VT, LHS, RHS);
- SDValue NotXor1 = DAG.getNOT(dl, Xor1, VT);
- SDValue Xor2 = DAG.getNode(ISD::XOR, dl, VT, Add, LHS);
-
- SDValue And = DAG.getNode(ISD::AND, dl, VT, NotXor1, Xor2);
+ // Compute ~(x xor y)
+ SDValue XorXY = DAG.getNode(ISD::XOR, dl, VT, LHS, RHS);
+ SDValue EqvXY = DAG.getNOT(dl, XorXY, VT);
+ // Compute (s xor x)
+ SDValue SumXorX = DAG.getNode(ISD::XOR, dl, VT, Sum, LHS);
+ // overflow = (x eqv y) & (s xor x)
+ SDValue OverflowInSign = DAG.getNode(ISD::AND, dl, VT, EqvXY, SumXorX);
+
+ // Shift sign bit down to LSB
SDValue Overflow =
- DAG.getNode(ISD::SRL, dl, VT, And,
+ DAG.getNode(ISD::SRL, dl, VT, OverflowInSign,
DAG.getConstant(VT.getSizeInBits() - 1, dl, MVT::i32));
-
+ // Truncate to the overflow type (i1)
SDValue OverflowTrunc =
DAG.getNode(ISD::TRUNCATE, dl, Op.getNode()->getValueType(1), Overflow);
- return DAG.getMergeValues({Add, OverflowTrunc}, dl);
+ return DAG.getMergeValues({Sum, OverflowTrunc}, dl);
}
/// LowerOperation - Provide custom lowering hooks for some operations.
>From 9bf6413fed22dd6ae4baf847e5fdf39c7996388b Mon Sep 17 00:00:00 2001
From: AditiRM <aditimedhane73 at gmail.com>
Date: Mon, 17 Nov 2025 08:15:07 +0000
Subject: [PATCH 4/4] fix clang format error
---
llvm/lib/Target/PowerPC/PPCISelLowering.cpp | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/llvm/lib/Target/PowerPC/PPCISelLowering.cpp b/llvm/lib/Target/PowerPC/PPCISelLowering.cpp
index 0dc33429fb3d6..db6af0126fb3a 100644
--- a/llvm/lib/Target/PowerPC/PPCISelLowering.cpp
+++ b/llvm/lib/Target/PowerPC/PPCISelLowering.cpp
@@ -12719,7 +12719,7 @@ SDValue PPCTargetLowering::LowerSADDO(SDValue Op, SelectionDAG &DAG) const {
// overflow = (x eqv y) & (s xor x)
SDValue OverflowInSign = DAG.getNode(ISD::AND, dl, VT, EqvXY, SumXorX);
-
+
// Shift sign bit down to LSB
SDValue Overflow =
DAG.getNode(ISD::SRL, dl, VT, OverflowInSign,
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