From e758ddcd16f701225ac673c5f38e2e04b9d24faa Mon Sep 17 00:00:00 2001 From: Juergen Ributzka Date: Fri, 24 Jan 2014 06:47:57 +0000 Subject: [X86] Prevent the creation of redundant ops for sadd and ssub with overflow. This commit teaches the X86 backend to create the same X86 instructions when it lowers an sadd/ssub with overflow intrinsic and a conditional branch that uses that overflow result. This allows SelectionDAG to recognize and remove one of the redundant operations. This fixes and . Reviewed by Nadav llvm-svn: 199976 --- llvm/lib/Target/X86/X86ISelLowering.cpp | 19 +++++++++++++++++-- 1 file changed, 17 insertions(+), 2 deletions(-) (limited to 'llvm/lib') diff --git a/llvm/lib/Target/X86/X86ISelLowering.cpp b/llvm/lib/Target/X86/X86ISelLowering.cpp index 4b30ff67c9f..03eb57a4084 100644 --- a/llvm/lib/Target/X86/X86ISelLowering.cpp +++ b/llvm/lib/Target/X86/X86ISelLowering.cpp @@ -10715,11 +10715,26 @@ SDValue X86TargetLowering::LowerBRCOND(SDValue Op, SelectionDAG &DAG) const { unsigned X86Opcode; unsigned X86Cond; SDVTList VTs; + // Keep this in sync with LowerXALUO, otherwise we might create redundant + // instructions that can't be removed afterwards (i.e. X86ISD::ADD and + // X86ISD::INC). switch (CondOpcode) { case ISD::UADDO: X86Opcode = X86ISD::ADD; X86Cond = X86::COND_B; break; - case ISD::SADDO: X86Opcode = X86ISD::ADD; X86Cond = X86::COND_O; break; + case ISD::SADDO: + if (ConstantSDNode *C = dyn_cast(RHS)) + if (C->isOne()) { + X86Opcode = X86ISD::INC; X86Cond = X86::COND_O; + break; + } + X86Opcode = X86ISD::ADD; X86Cond = X86::COND_O; break; case ISD::USUBO: X86Opcode = X86ISD::SUB; X86Cond = X86::COND_B; break; - case ISD::SSUBO: X86Opcode = X86ISD::SUB; X86Cond = X86::COND_O; break; + case ISD::SSUBO: + if (ConstantSDNode *C = dyn_cast(RHS)) + if (C->isOne()) { + X86Opcode = X86ISD::DEC; X86Cond = X86::COND_O; + break; + } + X86Opcode = X86ISD::SUB; X86Cond = X86::COND_O; break; case ISD::UMULO: X86Opcode = X86ISD::UMUL; X86Cond = X86::COND_O; break; case ISD::SMULO: X86Opcode = X86ISD::SMUL; X86Cond = X86::COND_O; break; default: llvm_unreachable("unexpected overflowing operator"); -- cgit v1.2.3