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Better optimize Shift-And constructs.

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This commit is contained in:
Wilson Snyder
2017-09-19 20:56:17 -04:00
parent 6006cdff2c
commit 393b5d48b2
4 changed files with 135 additions and 0 deletions
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src/V3Const.cpp
+28
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@@ -341,6 +341,33 @@ private:
replaceWChild(nodep, bip); VL_DANGLING(nodep);
return true;
}
bool operandSelShiftLower(AstSel* nodep) {
// AND({a}, SHIFTR({b}, {c})) is often shorthand in C for Verilog {b}[{c} :+ {a}]
// becomes thought other optimizations
// SEL(SHIFTR({a},{b}),{lsb},{width}) -> SEL({a},{lsb+b},{width})
AstShiftR* shiftp = nodep->fromp()->castShiftR();
if (!(m_doV
&& shiftp
&& shiftp->rhsp()->castConst()
&& nodep->lsbp()->castConst()
&& nodep->widthp()->castConst()
)) return false;
AstNode* ap = shiftp->lhsp();
AstConst* bp = shiftp->rhsp()->castConst();
AstConst* lp = nodep->lsbp()->castConst();
if (bp->isWide() || bp->num().isFourState() || bp->num().isNegative()
|| lp->isWide() || lp->num().isFourState() || lp->num().isNegative()) return false;
int newLsb = lp->toSInt() + bp->toSInt();
if (newLsb + nodep->widthConst() > ap->width()) return false;
//
UINFO(9, "SEL(SHIFTR(a,b),l,w) -> SEL(a,l+b,w)\n");
if (debug()>=9) nodep->dumpTree(cout,"SEL(SH)-in:");
AstSel* newp = new AstSel(nodep->fileline(), ap->unlinkFrBack(), newLsb, nodep->widthConst());
newp->dtypeFrom(nodep);
if (debug()>=9) newp->dumpTree(cout,"SEL(SH)-ou:");
nodep->replaceWith(newp); VL_DANGLING(nodep);
return true;
}
bool operandBiExtendConst(AstNodeBiop* nodep) {
// Loop unrolling favors standalone compares
@@ -2252,6 +2279,7 @@ private:
TREEOPV("AstSel{$fromp.castSub, operandSelBiLower(nodep)}", "DONE");
TREEOPV("AstSel{$fromp.castXnor,operandSelBiLower(nodep)}", "DONE");
TREEOPV("AstSel{$fromp.castXor, operandSelBiLower(nodep)}", "DONE");
TREEOPV("AstSel{$fromp.castShiftR, operandSelShiftLower(nodep)}", "DONE");
TREEOPC("AstSel{$fromp.castConst, $lsbp.castConst, $widthp.castConst, }", "replaceConst(nodep)");
TREEOPV("AstSel{$fromp.castConcat, $lsbp.castConst, $widthp.castConst, }", "replaceSelConcat(nodep)");
TREEOPV("AstSel{$fromp.castReplicate, $lsbp.castConst, $widthp.isOne, }", "replaceSelReplicate(nodep)");