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[ValueTracking] Add with.overflow intrinsics to poison analysis functions 

This is a patch teaching ValueTracking that `s/u*.with.overflow` intrinsics do not
create undef/poison and they propagate poison.
I couldn't write a nice example like the one with ctpop; ValueTrackingTest.cpp were simply updated
to check these instead.
This patch helps reducing regression while fixing https://llvm.org/pr49688 .

Reviewed By: nikic

Differential Revision: https://reviews.llvm.org/D99671
This commit is contained in:
Juneyoung Lee 2021-04-01 02:01:17 +09:00
parent ae7b1e8823
commit df0b97dab0
2 changed files with 59 additions and 6 deletions
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24
llvm/lib/Analysis/ValueTracking.cpp
View File

@ -4887,6 +4887,12 @@ static bool canCreateUndefOrPoison(const Operator *Op, bool PoisonOnly) {
switch (II->getIntrinsicID()) {
// TODO: Add more intrinsics.
case Intrinsic::ctpop:
case Intrinsic::sadd_with_overflow:
case Intrinsic::ssub_with_overflow:
case Intrinsic::smul_with_overflow:
case Intrinsic::uadd_with_overflow:
case Intrinsic::usub_with_overflow:
case Intrinsic::umul_with_overflow:
return false;
}
}
@ -5214,9 +5220,25 @@ bool llvm::propagatesPoison(const Operator *I) {
case Instruction::Freeze:
case Instruction::Select:
case Instruction::PHI:
case Instruction::Call:
case Instruction::Invoke:
return false;
case Instruction::Call:
if (auto *II = dyn_cast<IntrinsicInst>(I)) {
switch (II->getIntrinsicID()) {
// TODO: Add more intrinsics.
case Intrinsic::sadd_with_overflow:
case Intrinsic::ssub_with_overflow:
case Intrinsic::smul_with_overflow:
case Intrinsic::uadd_with_overflow:
case Intrinsic::usub_with_overflow:
case Intrinsic::umul_with_overflow:
// If an input is a vector containing a poison element, the
// two output vectors (calculated results, overflow bits)'
// corresponding lanes are poison.
return true;
}
}
return false;
case Instruction::ICmp:
case Instruction::FCmp:
case Instruction::GetElementPtr:

41
llvm/unittests/Analysis/ValueTrackingTest.cpp
View File

@ -805,9 +805,16 @@ TEST_F(ValueTrackingTest, ComputeNumSignBits_Shuffle_Pointers) {
}
TEST(ValueTracking, propagatesPoison) {
std::string AsmHead = "declare i32 @g(i32)\n"
"define void @f(i32 %x, i32 %y, float %fx, float %fy, "
"i1 %cond, i8* %p) {\n";
std::string AsmHead =
"declare i32 @g(i32)\n"
"declare {i32, i1} @llvm.sadd.with.overflow.i32(i32 %a, i32 %b)\n"
"declare {i32, i1} @llvm.ssub.with.overflow.i32(i32 %a, i32 %b)\n"
"declare {i32, i1} @llvm.smul.with.overflow.i32(i32 %a, i32 %b)\n"
"declare {i32, i1} @llvm.uadd.with.overflow.i32(i32 %a, i32 %b)\n"
"declare {i32, i1} @llvm.usub.with.overflow.i32(i32 %a, i32 %b)\n"
"declare {i32, i1} @llvm.umul.with.overflow.i32(i32 %a, i32 %b)\n"
"define void @f(i32 %x, i32 %y, float %fx, float %fy, "
"i1 %cond, i8* %p) {\n";
std::string AsmTail = " ret void\n}";
// (propagates poison?, IR instruction)
SmallVector<std::pair<bool, std::string>, 32> Data = {
@ -826,7 +833,13 @@ TEST(ValueTracking, propagatesPoison) {
{true, "urem i32 %x, %y"},
{true, "sdiv exact i32 %x, %y"},
{true, "srem i32 %x, %y"},
{false, "call i32 @g(i32 %x)"}};
{false, "call i32 @g(i32 %x)"},
{true, "call {i32, i1} @llvm.sadd.with.overflow.i32(i32 %x, i32 %y)"},
{true, "call {i32, i1} @llvm.ssub.with.overflow.i32(i32 %x, i32 %y)"},
{true, "call {i32, i1} @llvm.smul.with.overflow.i32(i32 %x, i32 %y)"},
{true, "call {i32, i1} @llvm.uadd.with.overflow.i32(i32 %x, i32 %y)"},
{true, "call {i32, i1} @llvm.usub.with.overflow.i32(i32 %x, i32 %y)"},
{true, "call {i32, i1} @llvm.umul.with.overflow.i32(i32 %x, i32 %y)"}};
std::string AssemblyStr = AsmHead;
for (auto &Itm : Data)
@ -992,6 +1005,12 @@ TEST(ValueTracking, canCreatePoisonOrUndef) {
std::string AsmHead =
"@s = external dso_local global i32, align 1\n"
"declare i32 @g(i32)\n"
"declare {i32, i1} @llvm.sadd.with.overflow.i32(i32 %a, i32 %b)\n"
"declare {i32, i1} @llvm.ssub.with.overflow.i32(i32 %a, i32 %b)\n"
"declare {i32, i1} @llvm.smul.with.overflow.i32(i32 %a, i32 %b)\n"
"declare {i32, i1} @llvm.uadd.with.overflow.i32(i32 %a, i32 %b)\n"
"declare {i32, i1} @llvm.usub.with.overflow.i32(i32 %a, i32 %b)\n"
"declare {i32, i1} @llvm.umul.with.overflow.i32(i32 %a, i32 %b)\n"
"define void @f(i32 %x, i32 %y, float %fx, float %fy, i1 %cond, "
"<4 x i32> %vx, <4 x i32> %vx2, <vscale x 4 x i32> %svx, i8* %p) {\n";
std::string AsmTail = " ret void\n}";
@ -1053,7 +1072,19 @@ TEST(ValueTracking, canCreatePoisonOrUndef) {
{{true, false},
"ashr <4 x i32> %vx, select (i1 icmp sgt (i32 ptrtoint (i32* @s to "
"i32), i32 1), <4 x i32> zeroinitializer, <4 x i32> <i32 0, i32 1, i32 "
"2, i32 3>)"}};
"2, i32 3>)"},
{{false, false},
"call {i32, i1} @llvm.sadd.with.overflow.i32(i32 %x, i32 %y)"},
{{false, false},
"call {i32, i1} @llvm.ssub.with.overflow.i32(i32 %x, i32 %y)"},
{{false, false},
"call {i32, i1} @llvm.smul.with.overflow.i32(i32 %x, i32 %y)"},
{{false, false},
"call {i32, i1} @llvm.uadd.with.overflow.i32(i32 %x, i32 %y)"},
{{false, false},
"call {i32, i1} @llvm.usub.with.overflow.i32(i32 %x, i32 %y)"},
{{false, false},
"call {i32, i1} @llvm.umul.with.overflow.i32(i32 %x, i32 %y)"}};
std::string AssemblyStr = AsmHead;
for (auto &Itm : Data)