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[ConstantRange] Shl considers full-set shifting to last bit position. 

if we do SHL of two 16-bit ranges like [0, 30000) with [1,2) we get
"full-set" instead of what I would have expected [0, 60000) which is
still in the 16-bit unsigned range.

This patch changes the SHL algorithm to allow getting a usable range
even in this case.

Differential Revision: https://reviews.llvm.org/D57983

llvm-svn: 357854
This commit is contained in:
Marcello Maggioni 2019-04-07 06:12:44 +00:00
parent 545ed223a6
commit 30eb575811
2 changed files with 11 additions and 1 deletions
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6
llvm/lib/IR/ConstantRange.cpp
View File

@ -1006,8 +1006,12 @@ ConstantRange::shl(const ConstantRange &Other) const {
APInt max = getUnsignedMax();
APInt Other_umax = Other.getUnsignedMax();
// If we are shifting by maximum amount of
// zero return return the original range.
if (Other_umax.isNullValue())
return *this;
// there's overflow!
if (Other_umax.uge(max.countLeadingZeros()))
if (Other_umax.ugt(max.countLeadingZeros()))
return getFull();
// FIXME: implement the other tricky cases

6
llvm/unittests/IR/ConstantRangeTest.cpp
View File

@ -704,6 +704,8 @@ TEST_F(ConstantRangeTest, UDiv) {
}
TEST_F(ConstantRangeTest, Shl) {
ConstantRange Some2(APInt(16, 0xfff), APInt(16, 0x8000));
ConstantRange WrapNullMax(APInt(16, 0x1), APInt(16, 0x0));
EXPECT_EQ(Full.shl(Full), Full);
EXPECT_EQ(Full.shl(Empty), Empty);
EXPECT_EQ(Full.shl(One), Full); // TODO: [0, (-1 << 0xa) + 1)
@ -720,6 +722,10 @@ TEST_F(ConstantRangeTest, Shl) {
EXPECT_EQ(Some.shl(Some), Full); // TODO: [0xa << 0xa, 0xfc01)
EXPECT_EQ(Some.shl(Wrap), Full); // TODO: [0xa, 0x7ff << 0x5 + 1)
EXPECT_EQ(Wrap.shl(Wrap), Full);
EXPECT_EQ(
Some2.shl(ConstantRange(APInt(16, 0x1))),
ConstantRange(APInt(16, 0xfff << 0x1), APInt(16, 0x7fff << 0x1) + 1));
EXPECT_EQ(One.shl(WrapNullMax), Full);
}
TEST_F(ConstantRangeTest, Lshr) {