[llvm] cbbbd5b - [GlobalISel] Make use of KnownBits::computeForAddSub
Jay Foad via llvm-commits
llvm-commits at lists.llvm.org
Mon Jan 27 14:26:23 PST 2020
Author: Jay Foad
Date: 2020-01-27T22:22:56Z
New Revision: cbbbd5b5f617f55fffd49920c97b006f1e8398c7
URL: https://github.com/llvm/llvm-project/commit/cbbbd5b5f617f55fffd49920c97b006f1e8398c7
DIFF: https://github.com/llvm/llvm-project/commit/cbbbd5b5f617f55fffd49920c97b006f1e8398c7.diff
LOG: [GlobalISel] Make use of KnownBits::computeForAddSub
Summary:
This is mostly NFC. computeForAddSub may give more precise results in
some cases, but that doesn't seem to affect any existing GlobalISel
tests.
Subscribers: rovka, hiraditya, volkan, Petar.Avramovic, llvm-commits
Tags: #llvm
Differential Revision: https://reviews.llvm.org/D73431
Added:
Modified:
llvm/lib/CodeGen/GlobalISel/GISelKnownBits.cpp
Removed:
################################################################################
diff --git a/llvm/lib/CodeGen/GlobalISel/GISelKnownBits.cpp b/llvm/lib/CodeGen/GlobalISel/GISelKnownBits.cpp
index 3dfac8e1cf13..87136e29eb2d 100644
--- a/llvm/lib/CodeGen/GlobalISel/GISelKnownBits.cpp
+++ b/llvm/lib/CodeGen/GlobalISel/GISelKnownBits.cpp
@@ -169,18 +169,12 @@ void GISelKnownBits::computeKnownBitsImpl(Register R, KnownBits &Known,
break;
}
case TargetOpcode::G_SUB: {
- // If low bits are known to be zero in both operands, then we know they are
- // going to be 0 in the result. Both addition and complement operations
- // preserve the low zero bits.
- computeKnownBitsImpl(MI.getOperand(1).getReg(), Known2, DemandedElts,
+ computeKnownBitsImpl(MI.getOperand(1).getReg(), Known, DemandedElts,
Depth + 1);
- unsigned KnownZeroLow = Known2.countMinTrailingZeros();
- if (KnownZeroLow == 0)
- break;
computeKnownBitsImpl(MI.getOperand(2).getReg(), Known2, DemandedElts,
Depth + 1);
- KnownZeroLow = std::min(KnownZeroLow, Known2.countMinTrailingZeros());
- Known.Zero.setLowBits(KnownZeroLow);
+ Known = KnownBits::computeForAddSub(/*Add*/ false, /*NSW*/ false, Known,
+ Known2);
break;
}
case TargetOpcode::G_XOR: {
@@ -204,24 +198,12 @@ void GISelKnownBits::computeKnownBitsImpl(Register R, KnownBits &Known,
LLVM_FALLTHROUGH;
}
case TargetOpcode::G_ADD: {
- // Output known-0 bits are known if clear or set in both the low clear bits
- // common to both LHS & RHS. For example, 8+(X<<3) is known to have the
- // low 3 bits clear.
- // Output known-0 bits are also known if the top bits of each input are
- // known to be clear. For example, if one input has the top 10 bits clear
- // and the other has the top 8 bits clear, we know the top 7 bits of the
- // output must be clear.
- computeKnownBitsImpl(MI.getOperand(1).getReg(), Known2, DemandedElts,
+ computeKnownBitsImpl(MI.getOperand(1).getReg(), Known, DemandedElts,
Depth + 1);
- unsigned KnownZeroHigh = Known2.countMinLeadingZeros();
- unsigned KnownZeroLow = Known2.countMinTrailingZeros();
computeKnownBitsImpl(MI.getOperand(2).getReg(), Known2, DemandedElts,
Depth + 1);
- KnownZeroHigh = std::min(KnownZeroHigh, Known2.countMinLeadingZeros());
- KnownZeroLow = std::min(KnownZeroLow, Known2.countMinTrailingZeros());
- Known.Zero.setLowBits(KnownZeroLow);
- if (KnownZeroHigh > 1)
- Known.Zero.setHighBits(KnownZeroHigh - 1);
+ Known =
+ KnownBits::computeForAddSub(/*Add*/ true, /*NSW*/ false, Known, Known2);
break;
}
case TargetOpcode::G_AND: {
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