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Followup to r60283: optimize arbitrary width signed divisions as well

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as unsigned divisions.  Same caveats as before.

llvm-svn: 60284
This commit is contained in:
Eli Friedman 2008-11-30 06:35:39 +00:00
parent d7a261120f
commit ccdfdbfc99
2 changed files with 44 additions and 71 deletions
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105
lib/CodeGen/SelectionDAG/TargetLowering.cpp
View File

@ -2224,7 +2224,7 @@ bool TargetLowering::isLegalAddressingMode(const AddrMode &AM,
struct mu {
APInt m; // magic number
bool a; // add indicator
uint32_t s; // shift amount
unsigned s; // shift amount
};
/// magicu - calculate the magic numbers required to codegen an integer udiv as
@ -2273,89 +2273,50 @@ static mu magicu(const APInt& d) {
}
// Magic for divide replacement
// FIXME: This should be APInt'ified
struct ms {
int64_t m; // magic number
int64_t s; // shift amount
APInt m; // magic number
unsigned s; // shift amount
};
/// magic - calculate the magic numbers required to codegen an integer sdiv as
/// a sequence of multiply and shifts. Requires that the divisor not be 0, 1,
/// or -1.
static ms magic32(int32_t d) {
int32_t p;
uint32_t ad, anc, delta, q1, r1, q2, r2, t;
const uint32_t two31 = 0x80000000U;
static ms magic(const APInt& d) {
unsigned p;
APInt ad, anc, delta, q1, r1, q2, r2, t;
APInt allOnes = APInt::getAllOnesValue(d.getBitWidth());
APInt signedMin = APInt::getSignedMinValue(d.getBitWidth());
APInt signedMax = APInt::getSignedMaxValue(d.getBitWidth());
struct ms mag;
ad = abs(d);
t = two31 + ((uint32_t)d >> 31);
anc = t - 1 - t%ad; // absolute value of nc
p = 31; // initialize p
q1 = two31/anc; // initialize q1 = 2p/abs(nc)
r1 = two31 - q1*anc; // initialize r1 = rem(2p,abs(nc))
q2 = two31/ad; // initialize q2 = 2p/abs(d)
r2 = two31 - q2*ad; // initialize r2 = rem(2p,abs(d))
ad = d.abs();
t = signedMin + (d.lshr(d.getBitWidth() - 1));
anc = t - 1 - t.urem(ad); // absolute value of nc
p = d.getBitWidth() - 1; // initialize p
q1 = signedMin.udiv(anc); // initialize q1 = 2p/abs(nc)
r1 = signedMin - q1*anc; // initialize r1 = rem(2p,abs(nc))
q2 = signedMin.udiv(ad); // initialize q2 = 2p/abs(d)
r2 = signedMin - q2*ad; // initialize r2 = rem(2p,abs(d))
do {
p = p + 1;
q1 = 2*q1; // update q1 = 2p/abs(nc)
r1 = 2*r1; // update r1 = rem(2p/abs(nc))
if (r1 >= anc) { // must be unsigned comparison
q1 = q1<<1; // update q1 = 2p/abs(nc)
r1 = r1<<1; // update r1 = rem(2p/abs(nc))
if (r1.uge(anc)) { // must be unsigned comparison
q1 = q1 + 1;
r1 = r1 - anc;
}
q2 = 2*q2; // update q2 = 2p/abs(d)
r2 = 2*r2; // update r2 = rem(2p/abs(d))
if (r2 >= ad) { // must be unsigned comparison
q2 = q2<<1; // update q2 = 2p/abs(d)
r2 = r2<<1; // update r2 = rem(2p/abs(d))
if (r2.uge(ad)) { // must be unsigned comparison
q2 = q2 + 1;
r2 = r2 - ad;
}
delta = ad - r2;
} while (q1 < delta || (q1 == delta && r1 == 0));
mag.m = (int32_t)(q2 + 1); // make sure to sign extend
if (d < 0) mag.m = -mag.m; // resulting magic number
mag.s = p - 32; // resulting shift
return mag;
}
/// magic - calculate the magic numbers required to codegen an integer sdiv as
/// a sequence of multiply and shifts. Requires that the divisor not be 0, 1,
/// or -1.
static ms magic64(int64_t d) {
int64_t p;
uint64_t ad, anc, delta, q1, r1, q2, r2, t;
const uint64_t two63 = 9223372036854775808ULL; // 2^63
struct ms mag;
ad = d >= 0 ? d : -d;
t = two63 + ((uint64_t)d >> 63);
anc = t - 1 - t%ad; // absolute value of nc
p = 63; // initialize p
q1 = two63/anc; // initialize q1 = 2p/abs(nc)
r1 = two63 - q1*anc; // initialize r1 = rem(2p,abs(nc))
q2 = two63/ad; // initialize q2 = 2p/abs(d)
r2 = two63 - q2*ad; // initialize r2 = rem(2p,abs(d))
do {
p = p + 1;
q1 = 2*q1; // update q1 = 2p/abs(nc)
r1 = 2*r1; // update r1 = rem(2p/abs(nc))
if (r1 >= anc) { // must be unsigned comparison
q1 = q1 + 1;
r1 = r1 - anc;
}
q2 = 2*q2; // update q2 = 2p/abs(d)
r2 = 2*r2; // update r2 = rem(2p/abs(d))
if (r2 >= ad) { // must be unsigned comparison
q2 = q2 + 1;
r2 = r2 - ad;
}
delta = ad - r2;
} while (q1 < delta || (q1 == delta && r1 == 0));
} while (q1.ule(delta) || (q1 == delta && r1 == 0));
mag.m = q2 + 1;
if (d < 0) mag.m = -mag.m; // resulting magic number
mag.s = p - 64; // resulting shift
if (d.isNegative()) mag.m = -mag.m; // resulting magic number
mag.s = p - d.getBitWidth(); // resulting shift
return mag;
}
@ -2368,13 +2329,15 @@ SDValue TargetLowering::BuildSDIV(SDNode *N, SelectionDAG &DAG,
MVT VT = N->getValueType(0);
// Check to see if we can do this.
if (!isTypeLegal(VT) || (VT != MVT::i32 && VT != MVT::i64))
return SDValue(); // BuildSDIV only operates on i32 or i64
// FIXME: We should be more aggressive here.
if (!isTypeLegal(VT))
return SDValue();
int64_t d = cast<ConstantSDNode>(N->getOperand(1))->getSExtValue();
ms magics = (VT == MVT::i32) ? magic32(d) : magic64(d);
APInt d = cast<ConstantSDNode>(N->getOperand(1))->getAPIntValue();
ms magics = magic(d);
// Multiply the numerator (operand 0) by the magic value
// FIXME: We should support doing a MUL in a wider type
SDValue Q;
if (isOperationLegal(ISD::MULHS, VT))
Q = DAG.getNode(ISD::MULHS, VT, N->getOperand(0),
@ -2386,13 +2349,13 @@ SDValue TargetLowering::BuildSDIV(SDNode *N, SelectionDAG &DAG,
else
return SDValue(); // No mulhs or equvialent
// If d > 0 and m < 0, add the numerator
if (d > 0 && magics.m < 0) {
if (d.isStrictlyPositive() && magics.m.isNegative()) {
Q = DAG.getNode(ISD::ADD, VT, Q, N->getOperand(0));
if (Created)
Created->push_back(Q.getNode());
}
// If d < 0 and m > 0, subtract the numerator.
if (d < 0 && magics.m > 0) {
if (d.isNegative() && magics.m.isStrictlyPositive()) {
Q = DAG.getNode(ISD::SUB, VT, Q, N->getOperand(0));
if (Created)
Created->push_back(Q.getNode());

10
test/CodeGen/X86/2008-11-29-DivideConstant16bitSigned.ll Normal file
View File

@ -0,0 +1,10 @@
; RUN: llvm-as < %s | llc -mtriple=i686-pc-linux-gnu | grep 63551
; ModuleID = '<stdin>'
target datalayout = "e-p:32:32:32-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:32:64-f32:32:32-f64:32:64-v64:64:64-v128:128:128-a0:0:64-f80:32:32"
target triple = "i686-pc-linux-gnu"
define signext i16 @a(i16 signext %x) nounwind {
entry:
%div = sdiv i16 %x, 33 ; <i32> [#uses=1]
ret i16 %div
}