[llvm] [ValueTracking] improve `isKnownNonZero` precision for `smax` (PR #88170)
via llvm-commits
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Tue Apr 9 22:42:02 PDT 2024
https://github.com/goldsteinn updated https://github.com/llvm/llvm-project/pull/88170
>From d5966f8530d564dbc76f2fcec04d38c2e3345ef3 Mon Sep 17 00:00:00 2001
From: Noah Goldstein <goldstein.w.n at gmail.com>
Date: Tue, 9 Apr 2024 12:36:03 -0500
Subject: [PATCH 1/2] [ValueTracking] Add tests for improving `isKnownNonZero`
of `smax`; NFC
---
.../Transforms/InstSimplify/known-non-zero.ll | 15 +++++++++++++++
1 file changed, 15 insertions(+)
diff --git a/llvm/test/Transforms/InstSimplify/known-non-zero.ll b/llvm/test/Transforms/InstSimplify/known-non-zero.ll
index b647f11af4461d..6ebc4e0f31a9cf 100644
--- a/llvm/test/Transforms/InstSimplify/known-non-zero.ll
+++ b/llvm/test/Transforms/InstSimplify/known-non-zero.ll
@@ -166,3 +166,18 @@ A:
B:
ret i1 0
}
+
+define i1 @smax_non_zero(i8 %xx, i8 %y) {
+; CHECK-LABEL: @smax_non_zero(
+; CHECK-NEXT: [[X0:%.*]] = and i8 [[XX:%.*]], 63
+; CHECK-NEXT: [[X:%.*]] = add i8 [[X0]], 1
+; CHECK-NEXT: [[V:%.*]] = call i8 @llvm.smax.i8(i8 [[X]], i8 [[Y:%.*]])
+; CHECK-NEXT: [[R:%.*]] = icmp eq i8 [[V]], 0
+; CHECK-NEXT: ret i1 [[R]]
+;
+ %x0 = and i8 %xx, 63
+ %x = add i8 %x0, 1
+ %v = call i8 @llvm.smax.i8(i8 %x, i8 %y)
+ %r = icmp eq i8 %v, 0
+ ret i1 %r
+}
>From 04547635f8076deb4a35fe78b8c9d16f1c8b5e7c Mon Sep 17 00:00:00 2001
From: Noah Goldstein <goldstein.w.n at gmail.com>
Date: Tue, 9 Apr 2024 11:58:03 -0500
Subject: [PATCH 2/2] [ValueTracking] improve `isKnownNonZero` precision for
`smax`
Instead of relying on known-bits for strictly positive, use the
`isKnownPositive` API. This will use `isKnownNonZero` which is more
accurate.
---
llvm/lib/Analysis/ValueTracking.cpp | 41 ++++++++++++++-----
.../Transforms/InstSimplify/known-non-zero.ll | 6 +--
2 files changed, 32 insertions(+), 15 deletions(-)
diff --git a/llvm/lib/Analysis/ValueTracking.cpp b/llvm/lib/Analysis/ValueTracking.cpp
index ca48cfe7738154..7bed69b58215d8 100644
--- a/llvm/lib/Analysis/ValueTracking.cpp
+++ b/llvm/lib/Analysis/ValueTracking.cpp
@@ -2828,23 +2828,44 @@ static bool isKnownNonZeroFromOperator(const Operator *I,
case Intrinsic::uadd_sat:
return isKnownNonZero(II->getArgOperand(1), DemandedElts, Depth, Q) ||
isKnownNonZero(II->getArgOperand(0), DemandedElts, Depth, Q);
- case Intrinsic::smin:
case Intrinsic::smax: {
- auto KnownOpImpliesNonZero = [&](const KnownBits &K) {
- return II->getIntrinsicID() == Intrinsic::smin
- ? K.isNegative()
- : K.isStrictlyPositive();
+ // If either arg is strictly positive the result is non-zero. Otherwise
+ // the result is non-zero if both ops are non-zero.
+ auto IsNonZero = [&](Value *Op, std::optional<bool> &OpNonZero,
+ KnownBits OpKnown) {
+ if (!OpNonZero.has_value())
+ OpNonZero = OpKnown.isNonZero() ||
+ isKnownNonZero(Op, DemandedElts, Depth, Q);
+ return *OpNonZero;
};
- KnownBits XKnown =
+ // Avoid re-computing isKnownNonZero.
+ std::optional<bool> Op0NonZero, Op1NonZero;
+ KnownBits Op1Known =
+ computeKnownBits(II->getArgOperand(1), DemandedElts, Depth, Q);
+ if (Op1Known.isNonNegative() &&
+ IsNonZero(II->getArgOperand(1), Op1NonZero, Op1Known))
+ return true;
+ KnownBits Op0Known =
computeKnownBits(II->getArgOperand(0), DemandedElts, Depth, Q);
- if (KnownOpImpliesNonZero(XKnown))
+ if (Op0Known.isNonNegative() &&
+ IsNonZero(II->getArgOperand(0), Op0NonZero, Op0Known))
return true;
- KnownBits YKnown =
+ return IsNonZero(II->getArgOperand(1), Op1NonZero, Op1Known) &&
+ IsNonZero(II->getArgOperand(0), Op0NonZero, Op0Known);
+ }
+ case Intrinsic::smin: {
+ // If either arg is negative the result is non-zero. Otherwise
+ // the result is non-zero if both ops are non-zero.
+ KnownBits Op1Known =
computeKnownBits(II->getArgOperand(1), DemandedElts, Depth, Q);
- if (KnownOpImpliesNonZero(YKnown))
+ if (Op1Known.isNegative())
+ return true;
+ KnownBits Op0Known =
+ computeKnownBits(II->getArgOperand(0), DemandedElts, Depth, Q);
+ if (Op0Known.isNegative())
return true;
- if (XKnown.isNonZero() && YKnown.isNonZero())
+ if (Op1Known.isNonZero() && Op0Known.isNonZero())
return true;
}
[[fallthrough]];
diff --git a/llvm/test/Transforms/InstSimplify/known-non-zero.ll b/llvm/test/Transforms/InstSimplify/known-non-zero.ll
index 6ebc4e0f31a9cf..51f80f62c2f34c 100644
--- a/llvm/test/Transforms/InstSimplify/known-non-zero.ll
+++ b/llvm/test/Transforms/InstSimplify/known-non-zero.ll
@@ -169,11 +169,7 @@ B:
define i1 @smax_non_zero(i8 %xx, i8 %y) {
; CHECK-LABEL: @smax_non_zero(
-; CHECK-NEXT: [[X0:%.*]] = and i8 [[XX:%.*]], 63
-; CHECK-NEXT: [[X:%.*]] = add i8 [[X0]], 1
-; CHECK-NEXT: [[V:%.*]] = call i8 @llvm.smax.i8(i8 [[X]], i8 [[Y:%.*]])
-; CHECK-NEXT: [[R:%.*]] = icmp eq i8 [[V]], 0
-; CHECK-NEXT: ret i1 [[R]]
+; CHECK-NEXT: ret i1 false
;
%x0 = and i8 %xx, 63
%x = add i8 %x0, 1
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