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[KnownBits] Add knownbits analysis for mulhs/mulu 'multiply high' instructions 

Split off from D98857

https://reviews.llvm.org/D98866
This commit is contained in:
Simon Pilgrim 2021-03-18 22:36:01 +00:00
parent 628f5c9da2
commit a96897219d
3 changed files with 43 additions and 1 deletions
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6
llvm/include/llvm/Support/KnownBits.h
View File

@ -296,6 +296,12 @@ public:
/// Compute known bits resulting from multiplying LHS and RHS.
static KnownBits computeForMul(const KnownBits &LHS, const KnownBits &RHS);
/// Compute known bits from sign-extended multiply-hi.
static KnownBits mulhs(const KnownBits &LHS, const KnownBits &RHS);
/// Compute known bits from zero-extended multiply-hi.
static KnownBits mulhu(const KnownBits &LHS, const KnownBits &RHS);
/// Compute known bits for udiv(LHS, RHS).
static KnownBits udiv(const KnownBits &LHS, const KnownBits &RHS);

18
llvm/lib/Support/KnownBits.cpp
View File

@ -489,6 +489,24 @@ KnownBits KnownBits::computeForMul(const KnownBits &LHS, const KnownBits &RHS) {
return Res;
}
KnownBits KnownBits::mulhs(const KnownBits &LHS, const KnownBits &RHS) {
unsigned BitWidth = LHS.getBitWidth();
assert(BitWidth == RHS.getBitWidth() && !LHS.hasConflict() &&
!RHS.hasConflict() && "Operand mismatch");
KnownBits WideLHS = LHS.sext(2 * BitWidth);
KnownBits WideRHS = RHS.sext(2 * BitWidth);
return computeForMul(WideLHS, WideRHS).extractBits(BitWidth, BitWidth);
}
KnownBits KnownBits::mulhu(const KnownBits &LHS, const KnownBits &RHS) {
unsigned BitWidth = LHS.getBitWidth();
assert(BitWidth == RHS.getBitWidth() && !LHS.hasConflict() &&
!RHS.hasConflict() && "Operand mismatch");
KnownBits WideLHS = LHS.zext(2 * BitWidth);
KnownBits WideRHS = RHS.zext(2 * BitWidth);
return computeForMul(WideLHS, WideRHS).extractBits(BitWidth, BitWidth);
}
KnownBits KnownBits::udiv(const KnownBits &LHS, const KnownBits &RHS) {
unsigned BitWidth = LHS.getBitWidth();
assert(!LHS.hasConflict() && !RHS.hasConflict());

20
llvm/unittests/Support/KnownBitsTest.cpp
View File

@ -113,6 +113,8 @@ TEST(KnownBitsTest, BinaryExhaustive) {
KnownBits KnownSMax(KnownAnd);
KnownBits KnownSMin(KnownAnd);
KnownBits KnownMul(KnownAnd);
KnownBits KnownMulHS(KnownAnd);
KnownBits KnownMulHU(KnownAnd);
KnownBits KnownUDiv(KnownAnd);
KnownBits KnownURem(KnownAnd);
KnownBits KnownSRem(KnownAnd);
@ -156,6 +158,14 @@ TEST(KnownBitsTest, BinaryExhaustive) {
KnownMul.One &= Res;
KnownMul.Zero &= ~Res;
Res = (N1.sext(2 * Bits) * N2.sext(2 * Bits)).extractBits(Bits, Bits);
KnownMulHS.One &= Res;
KnownMulHS.Zero &= ~Res;
Res = (N1.zext(2 * Bits) * N2.zext(2 * Bits)).extractBits(Bits, Bits);
KnownMulHU.One &= Res;
KnownMulHU.Zero &= ~Res;
if (!N2.isNullValue()) {
Res = N1.udiv(N2);
KnownUDiv.One &= Res;
@ -218,12 +228,20 @@ TEST(KnownBitsTest, BinaryExhaustive) {
EXPECT_EQ(KnownSMin.Zero, ComputedSMin.Zero);
EXPECT_EQ(KnownSMin.One, ComputedSMin.One);
// ComputedMul is conservatively correct, but not guaranteed to be
// The following are conservatively correct, but not guaranteed to be
// precise.
KnownBits ComputedMul = KnownBits::computeForMul(Known1, Known2);
EXPECT_TRUE(ComputedMul.Zero.isSubsetOf(KnownMul.Zero));
EXPECT_TRUE(ComputedMul.One.isSubsetOf(KnownMul.One));
KnownBits ComputedMulHS = KnownBits::mulhs(Known1, Known2);
EXPECT_TRUE(ComputedMulHS.Zero.isSubsetOf(KnownMulHS.Zero));
EXPECT_TRUE(ComputedMulHS.One.isSubsetOf(KnownMulHS.One));
KnownBits ComputedMulHU = KnownBits::mulhu(Known1, Known2);
EXPECT_TRUE(ComputedMulHU.Zero.isSubsetOf(KnownMulHU.Zero));
EXPECT_TRUE(ComputedMulHU.One.isSubsetOf(KnownMulHU.One));
KnownBits ComputedUDiv = KnownBits::udiv(Known1, Known2);
EXPECT_TRUE(ComputedUDiv.Zero.isSubsetOf(KnownUDiv.Zero));
EXPECT_TRUE(ComputedUDiv.One.isSubsetOf(KnownUDiv.One));