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InstCombine: (icmp eq B, 0) | (icmp ult A, B) -> (icmp ule A, B-1)

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This transform allows us to turn IR that looks like:
  %1 = icmp eq i64 %b, 0
  %2 = icmp ult i64 %a, %b
  %3 = or i1 %1, %2
  ret i1 %3

into:
  %0 = add i64 %b, -1
  %1 = icmp uge i64 %0, %a
  ret i1 %1

which means we go from lowering:
        cmpq    %rsi, %rdi
        setb    %cl
        testq   %rsi, %rsi
        sete    %al
        orb     %cl, %al
        ret

to lowering:
        decq    %rsi
        cmpq    %rdi, %rsi
        setae   %al
        ret


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@185677 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
David Majnemer 2013-07-05 00:31:17 +00:00
parent 5679d7da01
commit b1b738e036
2 changed files with 39 additions and 1 deletions
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29
lib/Transforms/InstCombine/InstCombineAndOrXor.cpp
View File

@ -1477,10 +1477,37 @@ Value *InstCombiner::FoldOrOfICmps(ICmpInst *LHS, ICmpInst *RHS) {
if (Value *V = foldLogOpOfMaskedICmps(LHS, RHS, ICmpInst::ICMP_NE, Builder))
return V;
// This only handles icmp of constants: (icmp1 A, C1) | (icmp2 B, C2).
Value *Val = LHS->getOperand(0), *Val2 = RHS->getOperand(0);
ConstantInt *LHSCst = dyn_cast<ConstantInt>(LHS->getOperand(1));
ConstantInt *RHSCst = dyn_cast<ConstantInt>(RHS->getOperand(1));
if (LHS->hasOneUse() || RHS->hasOneUse()) {
// (icmp eq B, 0) | (icmp ult A, B) -> (icmp ule A, B-1)
// (icmp eq B, 0) | (icmp ugt B, A) -> (icmp ule A, B-1)
Value *A = 0, *B = 0;
if (LHSCC == ICmpInst::ICMP_EQ && LHSCst && LHSCst->isZero()) {
B = Val;
if (RHSCC == ICmpInst::ICMP_ULT && Val == RHS->getOperand(1))
A = Val2;
else if (RHSCC == ICmpInst::ICMP_UGT && Val == Val2)
A = RHS->getOperand(1);
}
// (icmp ult A, B) | (icmp eq B, 0) -> (icmp ule A, B-1)
// (icmp ugt B, A) | (icmp eq B, 0) -> (icmp ule A, B-1)
else if (RHSCC == ICmpInst::ICMP_EQ && RHSCst && RHSCst->isZero()) {
B = Val2;
if (LHSCC == ICmpInst::ICMP_ULT && Val2 == LHS->getOperand(1))
A = Val;
else if (LHSCC == ICmpInst::ICMP_UGT && Val2 == Val)
A = LHS->getOperand(1);
}
if (A && B)
return Builder->CreateICmp(
ICmpInst::ICMP_UGE,
Builder->CreateAdd(B, ConstantInt::getSigned(B->getType(), -1)), A);
}
// This only handles icmp of constants: (icmp1 A, C1) | (icmp2 B, C2).
if (LHSCst == 0 || RHSCst == 0) return 0;
if (LHSCst == RHSCst && LHSCC == RHSCC) {

11
test/Transforms/InstCombine/icmp.ll
View File

@ -1102,3 +1102,14 @@ define i1 @icmp_shl_1_V_ult_2147483648(i32 %V) {
%cmp = icmp ult i32 %shl, 2147483648
ret i1 %cmp
}
; CEHCK: @or_icmp_eq_B_0_icmp_ult_A_B
; CHECK: [[SUB:%[a-z0-9]+]] = add i64 %b, -1
; CHECK-NEXT: [[CMP:%[a-z0-9]+]] = icmp uge i64 [[SUB]], %a
; CHECK-NEXT: ret i1 [[CMP]]
define i1 @or_icmp_eq_B_0_icmp_ult_A_B(i64 %a, i64 %b) {
%1 = icmp eq i64 %b, 0
%2 = icmp ult i64 %a, %b
%3 = or i1 %1, %2
ret i1 %3
}