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[ValueTracking] allow non-canonical shuffles when computing signbits

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This possibility is noted in D53987 for a different case,
so we need to adjust the existing code.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@345988 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Sanjay Patel 2018-11-02 15:51:47 +00:00
parent 1b82386f5e
commit 6709348e9f
2 changed files with 30 additions and 8 deletions
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18
lib/Analysis/ValueTracking.cpp
View File

@ -2511,27 +2511,29 @@ static unsigned ComputeNumSignBitsImpl(const Value *V, unsigned Depth,
// extended, shifted, etc).
return ComputeNumSignBits(U->getOperand(0), Depth + 1, Q);
case Instruction::ShuffleVector:
case Instruction::ShuffleVector: {
// If the shuffle mask contains any undefined elements, that element of the
// result is undefined. Propagating information from a source operand may
// not be correct in that case, so just bail out.
if (cast<ShuffleVectorInst>(U)->getMask()->containsUndefElement())
break;
assert((!isa<UndefValue>(U->getOperand(0)) ||
!isa<UndefValue>(U->getOperand(1)))
&& "Should have simplified shuffle with 2 undef inputs");
// If everything is undef, we can't say anything. This should be simplified.
Value *Op0 = U->getOperand(0), *Op1 = U->getOperand(1);
if (isa<UndefValue>(Op0) && isa<UndefValue>(Op1))
break;
// Look through shuffle of 1 source vector.
if (isa<UndefValue>(U->getOperand(0)))
return ComputeNumSignBits(U->getOperand(1), Depth + 1, Q);
if (isa<UndefValue>(U->getOperand(1)))
return ComputeNumSignBits(U->getOperand(0), Depth + 1, Q);
if (isa<UndefValue>(Op0))
return ComputeNumSignBits(Op1, Depth + 1, Q);
if (isa<UndefValue>(Op1))
return ComputeNumSignBits(Op0, Depth + 1, Q);
// TODO: We can look through shuffles of 2 sources by computing the minimum
// sign bits for each operand (similar to what we do for binops).
break;
}
}
// Finally, if we can prove that the top bits of the result are 0's or 1's,
// use this information.

20
unittests/Analysis/ValueTrackingTest.cpp
View File

@ -494,6 +494,26 @@ TEST(ValueTracking, ComputeNumSignBits_PR32045) {
EXPECT_EQ(ComputeNumSignBits(RVal, M->getDataLayout()), 1u);
}
// No guarantees for canonical IR in this analysis, so this just bails out.
TEST(ValueTracking, ComputeNumSignBits_Shuffle) {
StringRef Assembly = "define <2 x i32> @f() { "
" %val = shufflevector <2 x i32> undef, <2 x i32> undef, <2 x i32> <i32 0, i32 0> "
" ret <2 x i32> %val "
"} ";
LLVMContext Context;
SMDiagnostic Error;
auto M = parseAssemblyString(Assembly, Error, Context);
assert(M && "Bad assembly?");
auto *F = M->getFunction("f");
assert(F && "Bad assembly?");
auto *RVal =
cast<ReturnInst>(F->getEntryBlock().getTerminator())->getOperand(0);
EXPECT_EQ(ComputeNumSignBits(RVal, M->getDataLayout()), 1u);
}
TEST(ValueTracking, ComputeKnownBits) {
StringRef Assembly = "define i32 @f(i32 %a, i32 %b) { "
" %ash = mul i32 %a, 8 "