From 7a0678cae6c549a1e11ac0767e04c273c298c0b7 Mon Sep 17 00:00:00 2001 From: Christopher Lamb Date: Tue, 18 Dec 2007 21:32:20 +0000 Subject: [PATCH] Fold subtracts into integer compares vs. zero. This improves generate code for this case on X86 from _foo: movl $99, %ecx movl 4(%esp), %eax subl %eax, %ecx xorl %edx, %edx testl %ecx, %ecx cmovs %edx, %eax ret to _foo: xorl %ecx, %ecx movl 4(%esp), %eax cmpl $99, %eax cmovg %ecx, %eax ret git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@45173 91177308-0d34-0410-b5e6-96231b3b80d8 --- .../Scalar/InstructionCombining.cpp | 19 ++++++++++++++++++- 1 file changed, 18 insertions(+), 1 deletion(-) diff --git a/lib/Transforms/Scalar/InstructionCombining.cpp b/lib/Transforms/Scalar/InstructionCombining.cpp index 1e4b1c3693e..166b4844403 100644 --- a/lib/Transforms/Scalar/InstructionCombining.cpp +++ b/lib/Transforms/Scalar/InstructionCombining.cpp @@ -4793,7 +4793,24 @@ Instruction *InstCombiner::visitICmpInst(ICmpInst &I) { if (isa(Op1)) // X icmp undef -> undef return ReplaceInstUsesWith(I, UndefValue::get(Type::Int1Ty)); - + + // (icmp cond (sub m A) 0) -> + // (icmp cond m A) + { + ConstantInt *C1, *C2; + Value *A; + // Check both arguments of the compare for a matching subtract. + if (match(Op0, m_ConstantInt(C1)) && C1->getValue() == 0 && + match(Op1, m_Sub(m_ConstantInt(C2), m_Value(A)))) { + // We managed to fold the add into the RHS of the select condition. + return new ICmpInst(I.getPredicate(), A, C2); + } else if (match(Op1, m_ConstantInt(C1)) && C1->getValue() == 0 && + match(Op0, m_Sub(m_ConstantInt(C2), m_Value(A)))) { + // We managed to fold the add into the LHS of the select condition. + return new ICmpInst(I.getPredicate(), C2, A); + } + } + // icmp , - Global/Stack value // addresses never equal each other! We already know that Op0 != Op1. if ((isa(Op0) || isa(Op0) ||