Skip to content

[PowerPC] Lower ucmp using subtractions #146446

New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

Sign up for GitHub

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

Merged
merged 1 commit into from
Oct 11, 2025
Merged

[PowerPC] Lower ucmp using subtractions #146446

Show file tree
Hide file tree
Changes from all commits
Commits
Show all changes
1 commit
Select commit
File filter

Filter by extension

Filter by extension
Conversations
Failed to load comments.
Loading
Jump to
Jump to file
Failed to load files.
Loading
Diff view
Diff view
33 changes: 33 additions & 0 deletions llvm/lib/Target/PowerPC/PPCISelLowering.cpp
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -585,6 +585,10 @@ PPCTargetLowering::PPCTargetLowering(const PPCTargetMachine &TM,
// We cannot sextinreg(i1). Expand to shifts.
setOperationAction(ISD::SIGN_EXTEND_INREG, MVT::i1, Expand);

// Custom handling for PowerPC ucmp instruction
setOperationAction(ISD::UCMP, MVT::i32, Custom);
setOperationAction(ISD::UCMP, MVT::i64, isPPC64 ? Custom : Expand);

// NOTE: EH_SJLJ_SETJMP/_LONGJMP supported here is NOT intended to support
// SjLj exception handling but a light-weight setjmp/longjmp replacement to
// support continuation, user-level threading, and etc.. As a result, no
Expand Down Expand Up @@ -12618,6 +12622,33 @@ SDValue PPCTargetLowering::LowerSSUBO(SDValue Op, SelectionDAG &DAG) const {
return DAG.getMergeValues({Sub, OverflowTrunc}, dl);
}

// Lower unsigned 3-way compare producing -1/0/1.
SDValue PPCTargetLowering::LowerUCMP(SDValue Op, SelectionDAG &DAG) const {
SDLoc DL(Op);
SDValue A = DAG.getFreeze(Op.getOperand(0));
SDValue B = DAG.getFreeze(Op.getOperand(1));
EVT OpVT = A.getValueType(); // operand type
EVT ResVT = Op.getValueType(); // result type

// First compute diff = A - B (will become subf).
SDValue Diff = DAG.getNode(ISD::SUB, DL, OpVT, A, B);

// Generate B - A using SUBC to capture carry.
SDVTList VTs = DAG.getVTList(OpVT, MVT::i32);
SDValue SubC = DAG.getNode(PPCISD::SUBC, DL, VTs, B, A);
SDValue CA0 = SubC.getValue(1);

// t2 = A - B + CA0 using SUBE.
SDValue SubE1 = DAG.getNode(PPCISD::SUBE, DL, VTs, A, B, CA0);
SDValue CA1 = SubE1.getValue(1);

// res = diff - t2 + CA1 using SUBE (produces desired -1/0/1).
SDValue ResPair = DAG.getNode(PPCISD::SUBE, DL, VTs, Diff, SubE1, CA1);

// Extract the first result and truncate to result type if needed
return DAG.getSExtOrTrunc(ResPair.getValue(0), DL, ResVT);
}

/// LowerOperation - Provide custom lowering hooks for some operations.
///
SDValue PPCTargetLowering::LowerOperation(SDValue Op, SelectionDAG &DAG) const {
Expand Down Expand Up @@ -12722,6 +12753,8 @@ SDValue PPCTargetLowering::LowerOperation(SDValue Op, SelectionDAG &DAG) const {
case ISD::UADDO_CARRY:
case ISD::USUBO_CARRY:
return LowerADDSUBO_CARRY(Op, DAG);
case ISD::UCMP:
return LowerUCMP(Op, DAG);
}
}

Expand Down
1 change: 1 addition & 0 deletions llvm/lib/Target/PowerPC/PPCISelLowering.h
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -1318,6 +1318,7 @@ namespace llvm {
SDValue LowerIS_FPCLASS(SDValue Op, SelectionDAG &DAG) const;
SDValue LowerADDSUBO_CARRY(SDValue Op, SelectionDAG &DAG) const;
SDValue LowerADDSUBO(SDValue Op, SelectionDAG &DAG) const;
SDValue LowerUCMP(SDValue Op, SelectionDAG &DAG) const;
SDValue lowerToLibCall(const char *LibCallName, SDValue Op,
SelectionDAG &DAG) const;
SDValue lowerLibCallBasedOnType(const char *LibCallFloatName,
Expand Down
20 changes: 9 additions & 11 deletions llvm/test/CodeGen/PowerPC/memcmp.ll
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -6,12 +6,10 @@ define signext i32 @memcmp8(ptr nocapture readonly %buffer1, ptr nocapture reado
; CHECK: # %bb.0:
; CHECK-NEXT: ldbrx 3, 0, 3
; CHECK-NEXT: ldbrx 4, 0, 4
; CHECK-NEXT: cmpld 3, 4
; CHECK-NEXT: subc 3, 4, 3
; CHECK-NEXT: subfe 3, 4, 4
; CHECK-NEXT: li 4, -1
; CHECK-NEXT: neg 3, 3
; CHECK-NEXT: isellt 3, 4, 3
; CHECK-NEXT: subc 6, 4, 3
; CHECK-NEXT: sub 5, 3, 4
; CHECK-NEXT: subfe 3, 4, 3
; CHECK-NEXT: subfe 3, 3, 5
; CHECK-NEXT: extsw 3, 3
; CHECK-NEXT: blr
%call = tail call signext i32 @memcmp(ptr %buffer1, ptr %buffer2, i64 8)
Expand All @@ -23,11 +21,11 @@ define signext i32 @memcmp4(ptr nocapture readonly %buffer1, ptr nocapture reado
; CHECK: # %bb.0:
; CHECK-NEXT: lwbrx 3, 0, 3
; CHECK-NEXT: lwbrx 4, 0, 4
; CHECK-NEXT: cmplw 3, 4
; CHECK-NEXT: sub 5, 4, 3
; CHECK-NEXT: li 3, -1
; CHECK-NEXT: rldicl 5, 5, 1, 63
; CHECK-NEXT: isellt 3, 3, 5
; CHECK-NEXT: subc 6, 4, 3
; CHECK-NEXT: sub 5, 3, 4
; CHECK-NEXT: subfe 3, 4, 3
; CHECK-NEXT: subfe 3, 3, 5
; CHECK-NEXT: extsw 3, 3
; CHECK-NEXT: blr
%call = tail call signext i32 @memcmp(ptr %buffer1, ptr %buffer2, i64 4)
ret i32 %call
Expand Down
74 changes: 28 additions & 46 deletions llvm/test/CodeGen/PowerPC/ucmp.ll
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -4,12 +4,10 @@
define i8 @ucmp_8_8(i8 zeroext %x, i8 zeroext %y) nounwind {
; CHECK-LABEL: ucmp_8_8:
; CHECK: # %bb.0:
; CHECK-NEXT: cmplw 3, 4
; CHECK-NEXT: sub 5, 4, 3
; CHECK-NEXT: li 3, -1
; CHECK-NEXT: rldicl 5, 5, 1, 63
; CHECK-NEXT: rldic 3, 3, 0, 32
; CHECK-NEXT: isellt 3, 3, 5
; CHECK-NEXT: subc 6, 4, 3
; CHECK-NEXT: sub 5, 3, 4
; CHECK-NEXT: subfe 3, 4, 3
; CHECK-NEXT: subfe 3, 3, 5
; CHECK-NEXT: blr
%1 = call i8 @llvm.ucmp(i8 %x, i8 %y)
ret i8 %1
Expand All @@ -18,12 +16,10 @@ define i8 @ucmp_8_8(i8 zeroext %x, i8 zeroext %y) nounwind {
define i8 @ucmp_8_16(i16 zeroext %x, i16 zeroext %y) nounwind {
; CHECK-LABEL: ucmp_8_16:
; CHECK: # %bb.0:
; CHECK-NEXT: cmplw 3, 4
; CHECK-NEXT: sub 5, 4, 3
; CHECK-NEXT: li 3, -1
; CHECK-NEXT: rldicl 5, 5, 1, 63
; CHECK-NEXT: rldic 3, 3, 0, 32
; CHECK-NEXT: isellt 3, 3, 5
; CHECK-NEXT: subc 6, 4, 3
; CHECK-NEXT: sub 5, 3, 4
; CHECK-NEXT: subfe 3, 4, 3
; CHECK-NEXT: subfe 3, 3, 5
; CHECK-NEXT: blr
%1 = call i8 @llvm.ucmp(i16 %x, i16 %y)
ret i8 %1
Expand All @@ -32,14 +28,10 @@ define i8 @ucmp_8_16(i16 zeroext %x, i16 zeroext %y) nounwind {
define i8 @ucmp_8_32(i32 %x, i32 %y) nounwind {
; CHECK-LABEL: ucmp_8_32:
; CHECK: # %bb.0:
; CHECK-NEXT: clrldi 5, 4, 32
; CHECK-NEXT: clrldi 6, 3, 32
; CHECK-NEXT: sub 5, 5, 6
; CHECK-NEXT: cmplw 3, 4
; CHECK-NEXT: li 3, -1
; CHECK-NEXT: rldic 3, 3, 0, 32
; CHECK-NEXT: rldicl 5, 5, 1, 63
; CHECK-NEXT: isellt 3, 3, 5
; CHECK-NEXT: subc 6, 4, 3
; CHECK-NEXT: sub 5, 3, 4
; CHECK-NEXT: subfe 3, 4, 3
; CHECK-NEXT: subfe 3, 3, 5
; CHECK-NEXT: blr
%1 = call i8 @llvm.ucmp(i32 %x, i32 %y)
ret i8 %1
Expand All @@ -48,12 +40,10 @@ define i8 @ucmp_8_32(i32 %x, i32 %y) nounwind {
define i8 @ucmp_8_64(i64 %x, i64 %y) nounwind {
; CHECK-LABEL: ucmp_8_64:
; CHECK: # %bb.0:
; CHECK-NEXT: cmpld 3, 4
; CHECK-NEXT: subc 3, 4, 3
; CHECK-NEXT: subfe 3, 4, 4
; CHECK-NEXT: li 4, -1
; CHECK-NEXT: neg 3, 3
; CHECK-NEXT: isellt 3, 4, 3
; CHECK-NEXT: subc 6, 4, 3
; CHECK-NEXT: sub 5, 3, 4
; CHECK-NEXT: subfe 3, 4, 3
; CHECK-NEXT: subfe 3, 3, 5
; CHECK-NEXT: blr
%1 = call i8 @llvm.ucmp(i64 %x, i64 %y)
ret i8 %1
Expand Down Expand Up @@ -82,14 +72,10 @@ define i8 @ucmp_8_128(i128 %x, i128 %y) nounwind {
define i32 @ucmp_32_32(i32 %x, i32 %y) nounwind {
; CHECK-LABEL: ucmp_32_32:
; CHECK: # %bb.0:
; CHECK-NEXT: clrldi 5, 4, 32
; CHECK-NEXT: clrldi 6, 3, 32
; CHECK-NEXT: sub 5, 5, 6
; CHECK-NEXT: cmplw 3, 4
; CHECK-NEXT: li 3, -1
; CHECK-NEXT: rldic 3, 3, 0, 32
; CHECK-NEXT: rldicl 5, 5, 1, 63
; CHECK-NEXT: isellt 3, 3, 5
; CHECK-NEXT: subc 6, 4, 3
; CHECK-NEXT: sub 5, 3, 4
; CHECK-NEXT: subfe 3, 4, 3
; CHECK-NEXT: subfe 3, 3, 5
; CHECK-NEXT: blr
%1 = call i32 @llvm.ucmp(i32 %x, i32 %y)
ret i32 %1
Expand All @@ -98,12 +84,10 @@ define i32 @ucmp_32_32(i32 %x, i32 %y) nounwind {
define i32 @ucmp_32_64(i64 %x, i64 %y) nounwind {
; CHECK-LABEL: ucmp_32_64:
; CHECK: # %bb.0:
; CHECK-NEXT: cmpld 3, 4
; CHECK-NEXT: subc 3, 4, 3
; CHECK-NEXT: subfe 3, 4, 4
; CHECK-NEXT: li 4, -1
; CHECK-NEXT: neg 3, 3
; CHECK-NEXT: isellt 3, 4, 3
; CHECK-NEXT: subc 6, 4, 3
; CHECK-NEXT: sub 5, 3, 4
; CHECK-NEXT: subfe 3, 4, 3
; CHECK-NEXT: subfe 3, 3, 5
; CHECK-NEXT: blr
%1 = call i32 @llvm.ucmp(i64 %x, i64 %y)
ret i32 %1
Expand All @@ -112,12 +96,10 @@ define i32 @ucmp_32_64(i64 %x, i64 %y) nounwind {
define i64 @ucmp_64_64(i64 %x, i64 %y) nounwind {
; CHECK-LABEL: ucmp_64_64:
; CHECK: # %bb.0:
; CHECK-NEXT: subc 5, 4, 3
; CHECK-NEXT: cmpld 3, 4
; CHECK-NEXT: li 3, -1
; CHECK-NEXT: subfe 5, 4, 4
; CHECK-NEXT: neg 5, 5
; CHECK-NEXT: isellt 3, 3, 5
; CHECK-NEXT: subc 6, 4, 3
; CHECK-NEXT: sub 5, 3, 4
; CHECK-NEXT: subfe 3, 4, 3
; CHECK-NEXT: subfe 3, 3, 5
; CHECK-NEXT: blr
%1 = call i64 @llvm.ucmp(i64 %x, i64 %y)
ret i64 %1
Expand Down