[llvm] [PowerPC] Fix an LowerADDSUBO_CARRY error when converting carry bit for usubo_carry (PR #137809)

[zhijian lin via llvm-commits]

https://github.com/diggerlin created https://github.com/llvm/llvm-project/pull/137809

In PowerPC, if there is borrow happen in the sub , the  carry bit is zero (unset) , the carry bit is set if the borrow not happen,

For the carry ISD::USUBO_CARRY, The nodes produce two results: the normal result of the add or sub, and a boolean value that is 1 if and only if there is an outgoing carry/borrow.

so we need to convert the 1(borrow for ISD::USUBO_CARRY) to zero for PowerPC borrow,  and we need to convert the 0( not borrow for ISD::USUBO_CARRY) to 1 for PowerPC not borrow.



>From 08328ec873ea890f615edf5c858e39dcbd03bc83 Mon Sep 17 00:00:00 2001
From: zhijian <zhijian at ca.ibm.com>
Date: Tue, 29 Apr 2025 13:28:59 +0000
Subject: [PATCH] fix an LowerADDSUBO_CARRY error when convert carry bit for
 usubo_carry

---
 llvm/lib/Target/PowerPC/PPCISelLowering.cpp |  2 +-
 llvm/test/CodeGen/PowerPC/usubo_carry.ll    | 32 +++++++++++++++++++++
 2 files changed, 33 insertions(+), 1 deletion(-)
 create mode 100644 llvm/test/CodeGen/PowerPC/usubo_carry.ll

diff --git a/llvm/lib/Target/PowerPC/PPCISelLowering.cpp b/llvm/lib/Target/PowerPC/PPCISelLowering.cpp
index 1f75425752a78..fc224eafc1573 100644
--- a/llvm/lib/Target/PowerPC/PPCISelLowering.cpp
+++ b/llvm/lib/Target/PowerPC/PPCISelLowering.cpp
@@ -12213,7 +12213,7 @@ SDValue PPCTargetLowering::LowerADDSUBO_CARRY(SDValue Op,
   Opc = IsAdd ? PPCISD::ADDE : PPCISD::SUBE;
   if (!IsAdd)
     CarryOp = DAG.getNode(ISD::XOR, DL, CarryOp.getValueType(), CarryOp,
-                          DAG.getAllOnesConstant(DL, CarryOp.getValueType()));
+                          DAG.getConstant(1UL, DL, CarryOp.getValueType()));
   CarryOp = ConvertCarryValueToCarryFlag(VT, CarryOp, DAG, Subtarget);
   SDValue Sum = DAG.getNode(Opc, DL, DAG.getVTList(VT, MVT::i32),
                             Op.getOperand(0), Op.getOperand(1), CarryOp);
diff --git a/llvm/test/CodeGen/PowerPC/usubo_carry.ll b/llvm/test/CodeGen/PowerPC/usubo_carry.ll
new file mode 100644
index 0000000000000..3f6ec7520cd58
--- /dev/null
+++ b/llvm/test/CodeGen/PowerPC/usubo_carry.ll
@@ -0,0 +1,32 @@
+; RUN: llc -ppc-asm-full-reg-names -verify-machineinstrs \
+; RUN:   -mtriple=powerpc-ibm-aix -mcpu=pwr7 < %s | FileCheck %s
+
+define i64 @foo(i32 noundef %argc) #0 {
+entry:
+  %argc.addr = alloca i32, align 4
+  %num = alloca i64, align 8
+  store i32 %argc, ptr %argc.addr, align 4
+  %0 = load i32, ptr %argc.addr, align 4
+  %sub = sub nsw i32 %0, 2
+  %conv = sext i32 %sub to i64
+  store i64 %conv, ptr %num, align 8
+  %1 = load i64, ptr %num, align 8
+  %sub1 = sub nsw i64 0, %1
+  ret i64 %sub1
+}
+
+attributes #0 = { noinline nounwind optnone "frame-pointer"="all"  "stack-protector-buffer-size"="8" }
+
+; CHECK:      .foo:
+; CHECK-NEXT: # %bb.0:                                # %entry
+; CHECK-NEXT:   stw r3, -8(r1)
+; CHECK-NEXT:   lwz r3, -8(r1)
+; CHECK-NEXT:   addi r3, r3, -2
+; CHECK-NEXT:   srawi r4, r3, 31
+; CHECK-NEXT:   stw r3, -12(r1)
+; CHECK-NEXT:   stw r4, -16(r1)
+; CHECK-NEXT:   lwz r3, -16(r1)
+; CHECK-NEXT:   lwz r4, -12(r1)
+; CHECK-NEXT:   subfic r4, r4, 0
+; CHECK-NEXT:   subfze r3, r3
+; CHECK-NEXT:   blr