[llvm] r346071 - [ValueTracking] peek through 2-input shuffles in ComputeNumSignBits
Sanjay Patel via llvm-commits
llvm-commits at lists.llvm.org
Sat Nov 3 06:18:56 PDT 2018
Author: spatel
Date: Sat Nov 3 06:18:55 2018
New Revision: 346071
URL: http://llvm.org/viewvc/llvm-project?rev=346071&view=rev
Log:
[ValueTracking] peek through 2-input shuffles in ComputeNumSignBits
This patch gives the IR ComputeNumSignBits the same functionality as the
DAG version (the code is derived from the existing code).
This an extension of the single input shuffle analysis added with D53659.
Differential Revision: https://reviews.llvm.org/D53987
Modified:
llvm/trunk/lib/Analysis/ValueTracking.cpp
llvm/trunk/test/Transforms/InstCombine/logical-select.ll
llvm/trunk/unittests/Analysis/ValueTrackingTest.cpp
Modified: llvm/trunk/lib/Analysis/ValueTracking.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Analysis/ValueTracking.cpp?rev=346071&r1=346070&r2=346071&view=diff
==============================================================================
--- llvm/trunk/lib/Analysis/ValueTracking.cpp (original)
+++ llvm/trunk/lib/Analysis/ValueTracking.cpp Sat Nov 3 06:18:55 2018
@@ -2512,26 +2512,41 @@ static unsigned ComputeNumSignBitsImpl(c
return ComputeNumSignBits(U->getOperand(0), Depth + 1, Q);
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;
+ // TODO: This is copied almost directly from the SelectionDAG version of
+ // ComputeNumSignBits. It would be better if we could share common
+ // code. If not, make sure that changes are translated to the DAG.
- // 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))
+ // Collect the minimum number of sign bits that are shared by every vector
+ // element referenced by the shuffle.
+ auto *Shuf = cast<ShuffleVectorInst>(U);
+ int NumElts = Shuf->getOperand(0)->getType()->getVectorNumElements();
+ int NumMaskElts = Shuf->getMask()->getType()->getVectorNumElements();
+ APInt DemandedLHS(NumElts, 0), DemandedRHS(NumElts, 0);
+ for (int i = 0; i != NumMaskElts; ++i) {
+ int M = Shuf->getMaskValue(i);
+ assert(M < NumElts * 2 && "Invalid shuffle mask constant");
+ // For undef elements, we don't know anything about the common state of
+ // the shuffle result.
+ if (M == -1)
+ return 1;
+ if (M < NumElts)
+ DemandedLHS.setBit(M % NumElts);
+ else
+ DemandedRHS.setBit(M % NumElts);
+ }
+ Tmp = std::numeric_limits<unsigned>::max();
+ if (!!DemandedLHS)
+ Tmp = ComputeNumSignBits(Shuf->getOperand(0), Depth + 1, Q);
+ if (!!DemandedRHS) {
+ Tmp2 = ComputeNumSignBits(Shuf->getOperand(1), Depth + 1, Q);
+ Tmp = std::min(Tmp, Tmp2);
+ }
+ // If we don't know anything, early out and try computeKnownBits fall-back.
+ if (Tmp == 1)
break;
-
- // Look through shuffle of 1 source vector.
- 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;
+ assert(Tmp <= V->getType()->getScalarSizeInBits() &&
+ "Failed to determine minimum sign bits");
+ return Tmp;
}
}
Modified: llvm/trunk/test/Transforms/InstCombine/logical-select.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/InstCombine/logical-select.ll?rev=346071&r1=346070&r2=346071&view=diff
==============================================================================
--- llvm/trunk/test/Transforms/InstCombine/logical-select.ll (original)
+++ llvm/trunk/test/Transforms/InstCombine/logical-select.ll Sat Nov 3 06:18:55 2018
@@ -621,11 +621,9 @@ define <4 x i32> @computesignbits_throug
; CHECK-NEXT: [[SEXT1:%.*]] = sext <4 x i1> [[COND1:%.*]] to <4 x i32>
; CHECK-NEXT: [[SEXT2:%.*]] = sext <4 x i1> [[COND2:%.*]] to <4 x i32>
; CHECK-NEXT: [[COND:%.*]] = shufflevector <4 x i32> [[SEXT1]], <4 x i32> [[SEXT2]], <4 x i32> <i32 0, i32 2, i32 4, i32 6>
-; CHECK-NEXT: [[NOTCOND:%.*]] = xor <4 x i32> [[COND]], <i32 -1, i32 -1, i32 -1, i32 -1>
-; CHECK-NEXT: [[AND1:%.*]] = and <4 x i32> [[NOTCOND]], [[X:%.*]]
-; CHECK-NEXT: [[AND2:%.*]] = and <4 x i32> [[COND]], [[Y:%.*]]
-; CHECK-NEXT: [[SEL:%.*]] = or <4 x i32> [[AND1]], [[AND2]]
-; CHECK-NEXT: ret <4 x i32> [[SEL]]
+; CHECK-NEXT: [[TMP1:%.*]] = trunc <4 x i32> [[COND]] to <4 x i1>
+; CHECK-NEXT: [[TMP2:%.*]] = select <4 x i1> [[TMP1]], <4 x i32> [[Y:%.*]], <4 x i32> [[X:%.*]]
+; CHECK-NEXT: ret <4 x i32> [[TMP2]]
;
%sext1 = sext <4 x i1> %cond1 to <4 x i32>
%sext2 = sext <4 x i1> %cond2 to <4 x i32>
Modified: llvm/trunk/unittests/Analysis/ValueTrackingTest.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/unittests/Analysis/ValueTrackingTest.cpp?rev=346071&r1=346070&r2=346071&view=diff
==============================================================================
--- llvm/trunk/unittests/Analysis/ValueTrackingTest.cpp (original)
+++ llvm/trunk/unittests/Analysis/ValueTrackingTest.cpp Sat Nov 3 06:18:55 2018
@@ -514,7 +514,6 @@ TEST(ValueTracking, ComputeNumSignBits_S
EXPECT_EQ(ComputeNumSignBits(RVal, M->getDataLayout()), 1u);
}
-// FIXME:
// No guarantees for canonical IR in this analysis, so a shuffle element that
// references an undef value means this can't return any extra information.
TEST(ValueTracking, ComputeNumSignBits_Shuffle2) {
@@ -534,7 +533,7 @@ TEST(ValueTracking, ComputeNumSignBits_S
auto *RVal =
cast<ReturnInst>(F->getEntryBlock().getTerminator())->getOperand(0);
- EXPECT_EQ(ComputeNumSignBits(RVal, M->getDataLayout()), 32u);
+ EXPECT_EQ(ComputeNumSignBits(RVal, M->getDataLayout()), 1u);
}
TEST(ValueTracking, ComputeKnownBits) {
More information about the llvm-commits
mailing list