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Fix signed shift right optimization, bug715.

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This commit is contained in:
Wilson Snyder 2014-03-09 21:28:28 -04:00
parent 334e0e1ca6
commit 9e76078939
4 changed files with 22 additions and 10 deletions
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2
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@ -15,6 +15,8 @@ indicates the contributor was also the author of the fix; Thanks!
**** Fix missing VL_SHIFTRS_IQI with WIDTH warning, bug714. [Fabrizio Ferrandi]
**** Fix signed shift right optimization, bug715. [Fabrizio Ferrandi]
**** Fix internal error on "input x =" syntax error, bug716. [Lane Brooks]
**** Fix slice extraction from packed array, bug717. [Jan Egil Ruud]

24
include/verilated.h
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@ -1455,32 +1455,37 @@ static inline WDataOutP VL_SHIFTR_WWI(int obits,int,int,WDataOutP owp,WDataInP l
}
// EMIT_RULE: VL_SHIFTRS: oclean=false; lclean=clean, rclean==clean;
static inline IData VL_SHIFTRS_III(int obits, int, int, IData lhs, IData rhs) {
static inline IData VL_SHIFTRS_III(int obits, int lbits, int, IData lhs, IData rhs) {
// Note the C standard does not specify the >> operator as a arithmetic shift!
IData sign = -(lhs >> (obits-1)); // ffff_ffff if negative
IData signext = ~(VL_MASK_I(obits) >> rhs); // One with bits where we've shifted "past"
// IEEE says signed if output signed, but bit position from lbits;
// must use lbits for sign; lbits might != obits,
// an EXTEND(SHIFTRS(...)) can became a SHIFTRS(...) within same 32/64 bit word length
IData sign = -(lhs >> (lbits-1)); // ffff_ffff if negative
IData signext = ~(VL_MASK_I(lbits) >> rhs); // One with bits where we've shifted "past"
return (lhs >> rhs) | (sign & VL_CLEAN_II(obits,obits,signext));
}
static inline QData VL_SHIFTRS_QQI(int obits, int, int, QData lhs, IData rhs) {
QData sign = -(lhs >> (obits-1));
QData signext = ~(VL_MASK_Q(obits) >> rhs);
static inline QData VL_SHIFTRS_QQI(int obits, int lbits, int, QData lhs, IData rhs) {
QData sign = -(lhs >> (lbits-1));
QData signext = ~(VL_MASK_Q(lbits) >> rhs);
return (lhs >> rhs) | (sign & VL_CLEAN_QQ(obits,obits,signext));
}
static inline IData VL_SHIFTRS_IQI(int obits, int lbits, int rbits, QData lhs, IData rhs) {
return (IData)(VL_SHIFTRS_QQI(obits, lbits, rbits, lhs, rhs));
}
static inline WDataOutP VL_SHIFTRS_WWI(int obits,int,int,WDataOutP owp,WDataInP lwp, IData rd) {
static inline WDataOutP VL_SHIFTRS_WWI(int obits,int lbits,int,WDataOutP owp,WDataInP lwp, IData rd) {
int word_shift = VL_BITWORD_I(rd);
int bit_shift = VL_BITBIT_I(rd);
int lmsw = VL_WORDS_I(obits)-1;
IData sign = VL_SIGNONES_I(obits,lwp[lmsw]);
if ((int)rd >= obits) {
IData sign = VL_SIGNONES_I(lbits,lwp[lmsw]);
if ((int)rd >= obits) { // Shifting past end, sign in all of lbits
for (int i=0; i <= lmsw; i++) owp[i] = sign;
owp[lmsw] &= VL_MASK_I(lbits);
} else if (bit_shift==0) { // Aligned word shift (>>0,>>32,>>64 etc)
int copy_words = (VL_WORDS_I(obits)-word_shift);
for (int i=0; i < copy_words; i++) owp[i] = lwp[i+word_shift];
if (copy_words>=0) owp[copy_words-1] |= ~VL_MASK_I(obits) & sign;
for (int i=copy_words; i < VL_WORDS_I(obits); i++) owp[i] = sign;
owp[lmsw] &= VL_MASK_I(lbits);
} else {
int loffset = rd & VL_SIZEBITS_I;
int nbitsonright = 32-loffset; // bits that end up in lword (know loffset!=0)
@ -1495,6 +1500,7 @@ static inline WDataOutP VL_SHIFTRS_WWI(int obits,int,int,WDataOutP owp,WDataInP
}
if (words) owp[words-1] |= sign & ~VL_MASK_I(obits-loffset);
for (int i=words; i<VL_WORDS_I(obits); i++) owp[i] = sign;
owp[lmsw] &= VL_MASK_I(lbits);
}
return(owp);
}

2
src/V3AstNodes.h
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@ -3849,6 +3849,8 @@ struct AstShiftR : public AstNodeBiop {
virtual bool sizeMattersLhs() {return false;} virtual bool sizeMattersRhs() {return false;} // LHS size might be > output size, so don't want to force size
};
struct AstShiftRS : public AstNodeBiop {
// Shift right with sign extension, >>> operator
// Output data type's width determines which bit is used for sign extension
AstShiftRS(FileLine* fl, AstNode* lhsp, AstNode* rhsp, int setwidth=0)
: AstNodeBiop(fl, lhsp, rhsp) {
if (setwidth) { dtypeSetLogicSized(setwidth,setwidth,AstNumeric::SIGNED); }

4
src/V3Const.cpp
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@ -538,6 +538,8 @@ private:
void replaceWChild(AstNode* nodep, AstNode* childp) {
// NODE(..., CHILD(...)) -> CHILD(...)
childp->unlinkFrBackWithNext();
// If replacing a SEL for example, the data type comes from the parent (is less wide).
// This may adversly affect the operation of the node being replaced.
childp->dtypeFrom(nodep);
nodep->replaceWith(childp);
nodep->deleteTree(); nodep=NULL;
@ -1831,7 +1833,7 @@ private:
TREEOP1("AstGte {$lhsp.isAllOnes, $rhsp, $lhsp->width()==$rhsp->width()}", "replaceNumLimited(nodep,1)");
// Two level bubble pushing
TREEOP ("AstNot {$lhsp.castNot, $lhsp->width()==$lhsp->castNot()->lhsp()->width()}", "replaceWChild(nodep, $lhsp->op1p())"); // NOT(NOT(x))->x
TREEOP ("AstLogNot{$lhsp.castLogNot}", "replaceWChild(nodep, $lhsp->op1p())"); // NOT(NOT(x))->x
TREEOP ("AstLogNot{$lhsp.castLogNot}", "replaceWChild(nodep, $lhsp->op1p())"); // LOGNOT(LOGNOT(x))->x
TREEOPV("AstNot {$lhsp.castEqCase, $lhsp.width1}","AstNeqCase{$lhsp->op1p(),$lhsp->op2p()}");
TREEOP ("AstLogNot{$lhsp.castEqCase}", "AstNeqCase{$lhsp->op1p(),$lhsp->op2p()}");
TREEOPV("AstNot {$lhsp.castNeqCase, $lhsp.width1}","AstEqCase {$lhsp->op1p(),$lhsp->op2p()}");