[llvm] [InstCombine] Missed optimization for select a%2==0, (a/2*2)*(a/2*2), 0 (PR #92658)
Jorge Botto via llvm-commits
llvm-commits at lists.llvm.org
Sat Aug 3 10:57:11 PDT 2024
https://github.com/jf-botto updated https://github.com/llvm/llvm-project/pull/92658
>From a860a3dfaabb42b73aabd8286edf56bb0bb6822a Mon Sep 17 00:00:00 2001
From: Jorge Botto <jorge.botto.16 at ucl.ac.uk>
Date: Sat, 27 Jul 2024 22:56:40 +0100
Subject: [PATCH 1/2] precommit test
---
.../InstCombine/select-known-bits.ll | 125 ++++++++++++++++++
1 file changed, 125 insertions(+)
create mode 100644 llvm/test/Transforms/InstCombine/select-known-bits.ll
diff --git a/llvm/test/Transforms/InstCombine/select-known-bits.ll b/llvm/test/Transforms/InstCombine/select-known-bits.ll
new file mode 100644
index 0000000000000..a4332f2f1d56e
--- /dev/null
+++ b/llvm/test/Transforms/InstCombine/select-known-bits.ll
@@ -0,0 +1,125 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --version 5
+; RUN: opt < %s -passes=instcombine -S | FileCheck %s
+
+define i8 @select_icmp_eq_mul_and(i8 noundef %a, i8 %b) {
+; CHECK-LABEL: define i8 @select_icmp_eq_mul_and(
+; CHECK-SAME: i8 noundef [[A:%.*]], i8 [[B:%.*]]) {
+; CHECK-NEXT: [[TMP1:%.*]] = and i8 [[A]], 1
+; CHECK-NEXT: [[CMP:%.*]] = icmp eq i8 [[TMP1]], 0
+; CHECK-NEXT: [[DIV:%.*]] = and i8 [[A]], -2
+; CHECK-NEXT: [[MUL:%.*]] = mul i8 [[DIV]], [[DIV]]
+; CHECK-NEXT: [[RETVAL:%.*]] = select i1 [[CMP]], i8 [[MUL]], i8 [[B]]
+; CHECK-NEXT: ret i8 [[RETVAL]]
+;
+ %1 = and i8 %a, 1
+ %cmp = icmp eq i8 %1, 0
+ %div = and i8 %a, -2
+ %mul = mul i8 %div, %div
+ %retval = select i1 %cmp, i8 %mul, i8 %b
+ ret i8 %retval
+}
+
+define i8 @select_icmp_eq_mul_and_inv(i8 noundef %a, i8 %b) {
+; CHECK-LABEL: define i8 @select_icmp_eq_mul_and_inv(
+; CHECK-SAME: i8 noundef [[A:%.*]], i8 [[B:%.*]]) {
+; CHECK-NEXT: [[TMP1:%.*]] = and i8 [[A]], 1
+; CHECK-NEXT: [[CMP_NOT:%.*]] = icmp eq i8 [[TMP1]], 0
+; CHECK-NEXT: [[DIV:%.*]] = and i8 [[A]], -2
+; CHECK-NEXT: [[MUL:%.*]] = mul i8 [[DIV]], [[DIV]]
+; CHECK-NEXT: [[RETVAL:%.*]] = select i1 [[CMP_NOT]], i8 [[MUL]], i8 [[B]]
+; CHECK-NEXT: ret i8 [[RETVAL]]
+;
+ %1 = and i8 %a, 1
+ %cmp = icmp eq i8 %1, 1
+ %div = and i8 %a, -2
+ %mul = mul i8 %div, %div
+ %retval = select i1 %cmp, i8 %b, i8 %mul
+ ret i8 %retval
+}
+
+define i8 @select_icmp_eq_and(i8 noundef %a, i8 %b) {
+; CHECK-LABEL: define i8 @select_icmp_eq_and(
+; CHECK-SAME: i8 noundef [[A:%.*]], i8 [[B:%.*]]) {
+; CHECK-NEXT: [[TMP1:%.*]] = and i8 [[A]], 1
+; CHECK-NEXT: [[CMP:%.*]] = icmp eq i8 [[TMP1]], 0
+; CHECK-NEXT: [[DIV:%.*]] = and i8 [[A]], -2
+; CHECK-NEXT: [[RETVAL:%.*]] = select i1 [[CMP]], i8 [[DIV]], i8 [[B]]
+; CHECK-NEXT: ret i8 [[RETVAL]]
+;
+ %1 = and i8 %a, 1
+ %cmp = icmp eq i8 %1, 0
+ %div = and i8 %a, -2
+ %retval = select i1 %cmp, i8 %div, i8 %b
+ ret i8 %retval
+}
+
+define i8 @select_icmp_eq_and_inv(i8 noundef %a, i8 %b) {
+; CHECK-LABEL: define i8 @select_icmp_eq_and_inv(
+; CHECK-SAME: i8 noundef [[A:%.*]], i8 [[B:%.*]]) {
+; CHECK-NEXT: [[TMP1:%.*]] = and i8 [[A]], 1
+; CHECK-NEXT: [[CMP_NOT:%.*]] = icmp eq i8 [[TMP1]], 0
+; CHECK-NEXT: [[DIV:%.*]] = and i8 [[A]], -2
+; CHECK-NEXT: [[RETVAL:%.*]] = select i1 [[CMP_NOT]], i8 [[DIV]], i8 [[B]]
+; CHECK-NEXT: ret i8 [[RETVAL]]
+;
+ %1 = and i8 %a, 1
+ %cmp = icmp eq i8 %1, 1
+ %div = and i8 %a, -2
+ %retval = select i1 %cmp, i8 %b, i8 %div
+ ret i8 %retval
+}
+
+;negative test
+define i8 @select_icmp_eq_and_undef(i8 %a, i8 %b) {
+; CHECK-LABEL: define i8 @select_icmp_eq_and_undef(
+; CHECK-SAME: i8 [[A:%.*]], i8 [[B:%.*]]) {
+; CHECK-NEXT: [[TMP1:%.*]] = and i8 [[A]], 1
+; CHECK-NEXT: [[CMP:%.*]] = icmp eq i8 [[TMP1]], 0
+; CHECK-NEXT: [[DIV:%.*]] = and i8 [[A]], -2
+; CHECK-NEXT: [[RETVAL:%.*]] = select i1 [[CMP]], i8 [[DIV]], i8 [[B]]
+; CHECK-NEXT: ret i8 [[RETVAL]]
+;
+ %1 = and i8 %a, 1
+ %cmp = icmp eq i8 %1, 0
+ %div = and i8 %a, -2
+ %retval = select i1 %cmp, i8 %div, i8 %b
+ ret i8 %retval
+}
+
+;negative test
+define i8 @select_icmp_eq_and_diff(i8 noundef %a, i8 %b, i8 %c) {
+; CHECK-LABEL: define i8 @select_icmp_eq_and_diff(
+; CHECK-SAME: i8 noundef [[A:%.*]], i8 [[B:%.*]], i8 [[C:%.*]]) {
+; CHECK-NEXT: [[TMP1:%.*]] = and i8 [[A]], 1
+; CHECK-NEXT: [[CMP:%.*]] = icmp eq i8 [[TMP1]], 0
+; CHECK-NEXT: [[DIV:%.*]] = and i8 [[C]], -2
+; CHECK-NEXT: [[RETVAL:%.*]] = select i1 [[CMP]], i8 [[DIV]], i8 [[B]]
+; CHECK-NEXT: ret i8 [[RETVAL]]
+;
+ %1 = and i8 %a, 1
+ %cmp = icmp eq i8 %1, 0
+ %div = and i8 %c, -2
+ %retval = select i1 %cmp, i8 %div, i8 %b
+ ret i8 %retval
+}
+
+;negative test
+define i8 @select_icmp_eq_mul_and_extra_use(i8 noundef %a, i8 %b) {
+; CHECK-LABEL: define i8 @select_icmp_eq_mul_and_extra_use(
+; CHECK-SAME: i8 noundef [[A:%.*]], i8 [[B:%.*]]) {
+; CHECK-NEXT: [[TMP1:%.*]] = and i8 [[A]], 1
+; CHECK-NEXT: [[CMP:%.*]] = icmp eq i8 [[TMP1]], 0
+; CHECK-NEXT: [[DIV:%.*]] = and i8 [[A]], -2
+; CHECK-NEXT: [[MUL:%.*]] = mul i8 [[DIV]], [[DIV]]
+; CHECK-NEXT: [[RETVAL:%.*]] = select i1 [[CMP]], i8 [[MUL]], i8 [[B]]
+; CHECK-NEXT: [[SUM:%.*]] = add i8 [[MUL]], [[RETVAL]]
+; CHECK-NEXT: ret i8 [[SUM]]
+;
+ %1 = and i8 %a, 1
+ %cmp = icmp eq i8 %1, 0
+ %div = and i8 %a, -2
+ %mul = mul i8 %div, %div
+ %retval = select i1 %cmp, i8 %mul, i8 %b
+ %sum = add i8 %mul, %retval
+ ret i8 %sum
+}
>From bf113b827fa4c34d30ae8b0075f735e24e4f46e3 Mon Sep 17 00:00:00 2001
From: Jorge Botto <jorge.botto.16 at ucl.ac.uk>
Date: Sat, 3 Aug 2024 14:43:02 +0100
Subject: [PATCH 2/2] Adding missed optimisation
---
llvm/include/llvm/Analysis/ValueTracking.h | 4 ++
.../Transforms/InstCombine/InstCombiner.h | 7 +++
llvm/lib/Analysis/ValueTracking.cpp | 6 +-
.../InstCombine/InstCombineSelect.cpp | 63 +++++++++++++++++++
.../InstCombine/select-known-bits.ll | 12 ++--
llvm/test/Transforms/InstCombine/select.ll | 11 ++--
6 files changed, 85 insertions(+), 18 deletions(-)
diff --git a/llvm/include/llvm/Analysis/ValueTracking.h b/llvm/include/llvm/Analysis/ValueTracking.h
index 96fa16970584d..c1ee4c02e0108 100644
--- a/llvm/include/llvm/Analysis/ValueTracking.h
+++ b/llvm/include/llvm/Analysis/ValueTracking.h
@@ -94,6 +94,10 @@ void computeKnownBitsFromRangeMetadata(const MDNode &Ranges, KnownBits &Known);
void computeKnownBitsFromContext(const Value *V, KnownBits &Known,
unsigned Depth, const SimplifyQuery &Q);
+void computeKnownBitsFromCond(const Value *V, Value *Cond, KnownBits &Known,
+ unsigned Depth, const SimplifyQuery &SQ,
+ bool Invert);
+
/// Using KnownBits LHS/RHS produce the known bits for logic op (and/xor/or).
KnownBits analyzeKnownBitsFromAndXorOr(const Operator *I,
const KnownBits &KnownLHS,
diff --git a/llvm/include/llvm/Transforms/InstCombine/InstCombiner.h b/llvm/include/llvm/Transforms/InstCombine/InstCombiner.h
index ebcbd5d9e8880..27bcaad49e5b4 100644
--- a/llvm/include/llvm/Transforms/InstCombine/InstCombiner.h
+++ b/llvm/include/llvm/Transforms/InstCombine/InstCombiner.h
@@ -438,6 +438,13 @@ class LLVM_LIBRARY_VISIBILITY InstCombiner {
return llvm::computeKnownBits(V, Depth, SQ.getWithInstruction(CxtI));
}
+ void computeKnownBitsFromCond(const Value *V, Value *Cmp, KnownBits &Known,
+ unsigned Depth, const Instruction *CxtI,
+ bool Invert) const {
+ llvm::computeKnownBitsFromCond(V, Cmp, Known, Depth,
+ SQ.getWithInstruction(CxtI), Invert);
+ }
+
bool isKnownToBeAPowerOfTwo(const Value *V, bool OrZero = false,
unsigned Depth = 0,
const Instruction *CxtI = nullptr) {
diff --git a/llvm/lib/Analysis/ValueTracking.cpp b/llvm/lib/Analysis/ValueTracking.cpp
index 285284dc27071..0d2d2d3bbbdbf 100644
--- a/llvm/lib/Analysis/ValueTracking.cpp
+++ b/llvm/lib/Analysis/ValueTracking.cpp
@@ -752,9 +752,9 @@ static void computeKnownBitsFromICmpCond(const Value *V, ICmpInst *Cmp,
computeKnownBitsFromCmp(V, Pred, LHS, RHS, Known, SQ);
}
-static void computeKnownBitsFromCond(const Value *V, Value *Cond,
- KnownBits &Known, unsigned Depth,
- const SimplifyQuery &SQ, bool Invert) {
+void llvm::computeKnownBitsFromCond(const Value *V, Value *Cond,
+ KnownBits &Known, unsigned Depth,
+ const SimplifyQuery &SQ, bool Invert) {
Value *A, *B;
if (Depth < MaxAnalysisRecursionDepth &&
match(Cond, m_LogicalOp(m_Value(A), m_Value(B)))) {
diff --git a/llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp b/llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp
index a22ee1de0ac21..eaa8faaa2db0f 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp
@@ -1078,6 +1078,62 @@ static Value *foldAbsDiff(ICmpInst *Cmp, Value *TVal, Value *FVal,
return nullptr;
}
+/// Attempts to fold (AND %A constant) --> %A
+/// if all bits that are zero in the negated constant
+/// are also zero in A's known zero bits.
+static Value *foldAndMaskPattern(Value *V, Value *Cmp, SelectInst &SI,
+ InstCombinerImpl &IC, unsigned Depth = 0) {
+
+ Value *A;
+ const APInt *MaskedConstant;
+
+ if (match(V, m_And(m_Value(A), m_APInt(MaskedConstant))) &&
+ isGuaranteedNotToBeUndef(A)) {
+ KnownBits Known = IC.computeKnownBits(A, 0, &SI);
+ IC.computeKnownBitsFromCond(A, Cmp, Known, 0, &SI, false);
+ if ((~(*MaskedConstant)).isSubsetOf(Known.Zero))
+ return A;
+ }
+
+ auto *I = dyn_cast<Instruction>(V);
+ if (!I || !isSafeToSpeculativelyExecute(I) || Depth >= 2)
+ return nullptr;
+
+ bool Changed = false;
+ for (unsigned i = 0; i < I->getNumOperands(); ++i) {
+ llvm::Value *Operand = I->getOperand(i);
+
+ if (std::any_of(Operand->user_begin(), Operand->user_end(),
+ [I](const User *User) { return User != I; }))
+ break;
+
+ Value *NewOp = foldAndMaskPattern(Operand, Cmp, SI, IC, Depth + 1);
+ if (NewOp) {
+ IC.replaceOperand(*I, i, NewOp);
+ Changed = true;
+ }
+ }
+
+ return Changed ? I : nullptr;
+}
+
+/// Attmpts to fold expressions in both branches of a select instruction
+/// based on KnownBits implied by the condition
+// static Instruction *foldSelectWithIcmpEqAndPattern(Value *TVal, Value *FVal,
+// Value *CondVal,
+// SelectInst &SI,
+// InstCombinerImpl &IC) {
+// if (TVal->hasOneUse())
+// if (Value *newTrueOp = simplifyAndMaskPattern(TVal, CondVal, SI, IC))
+// return IC.replaceOperand(SI, 1, newTrueOp);
+
+// if (FVal->hasOneUse())
+// if (Value *newFalseOp = simplifyAndMaskPattern(FVal, CondVal, SI, IC))
+// return IC.replaceOperand(SI, 2, newFalseOp);
+
+// return nullptr;
+// }
+
/// Fold the following code sequence:
/// \code
/// int a = ctlz(x & -x);
@@ -4110,5 +4166,12 @@ Instruction *InstCombinerImpl::visitSelectInst(SelectInst &SI) {
}
}
+ // Attempts to recursively identify and fold (AND A constant) --> A
+ // in the true branch of the select if all bits
+ // that are zero in the negated constant are also zero in A's known zero bits.
+ if (TrueVal->hasOneUse())
+ if (Value *newTrueOp = foldAndMaskPattern(TrueVal, CondVal, SI, *this))
+ return replaceOperand(SI, 1, newTrueOp);
+
return nullptr;
}
diff --git a/llvm/test/Transforms/InstCombine/select-known-bits.ll b/llvm/test/Transforms/InstCombine/select-known-bits.ll
index a4332f2f1d56e..52c56bed429a0 100644
--- a/llvm/test/Transforms/InstCombine/select-known-bits.ll
+++ b/llvm/test/Transforms/InstCombine/select-known-bits.ll
@@ -6,8 +6,7 @@ define i8 @select_icmp_eq_mul_and(i8 noundef %a, i8 %b) {
; CHECK-SAME: i8 noundef [[A:%.*]], i8 [[B:%.*]]) {
; CHECK-NEXT: [[TMP1:%.*]] = and i8 [[A]], 1
; CHECK-NEXT: [[CMP:%.*]] = icmp eq i8 [[TMP1]], 0
-; CHECK-NEXT: [[DIV:%.*]] = and i8 [[A]], -2
-; CHECK-NEXT: [[MUL:%.*]] = mul i8 [[DIV]], [[DIV]]
+; CHECK-NEXT: [[MUL:%.*]] = mul i8 [[A]], [[A]]
; CHECK-NEXT: [[RETVAL:%.*]] = select i1 [[CMP]], i8 [[MUL]], i8 [[B]]
; CHECK-NEXT: ret i8 [[RETVAL]]
;
@@ -24,8 +23,7 @@ define i8 @select_icmp_eq_mul_and_inv(i8 noundef %a, i8 %b) {
; CHECK-SAME: i8 noundef [[A:%.*]], i8 [[B:%.*]]) {
; CHECK-NEXT: [[TMP1:%.*]] = and i8 [[A]], 1
; CHECK-NEXT: [[CMP_NOT:%.*]] = icmp eq i8 [[TMP1]], 0
-; CHECK-NEXT: [[DIV:%.*]] = and i8 [[A]], -2
-; CHECK-NEXT: [[MUL:%.*]] = mul i8 [[DIV]], [[DIV]]
+; CHECK-NEXT: [[MUL:%.*]] = mul i8 [[A]], [[A]]
; CHECK-NEXT: [[RETVAL:%.*]] = select i1 [[CMP_NOT]], i8 [[MUL]], i8 [[B]]
; CHECK-NEXT: ret i8 [[RETVAL]]
;
@@ -42,8 +40,7 @@ define i8 @select_icmp_eq_and(i8 noundef %a, i8 %b) {
; CHECK-SAME: i8 noundef [[A:%.*]], i8 [[B:%.*]]) {
; CHECK-NEXT: [[TMP1:%.*]] = and i8 [[A]], 1
; CHECK-NEXT: [[CMP:%.*]] = icmp eq i8 [[TMP1]], 0
-; CHECK-NEXT: [[DIV:%.*]] = and i8 [[A]], -2
-; CHECK-NEXT: [[RETVAL:%.*]] = select i1 [[CMP]], i8 [[DIV]], i8 [[B]]
+; CHECK-NEXT: [[RETVAL:%.*]] = select i1 [[CMP]], i8 [[A]], i8 [[B]]
; CHECK-NEXT: ret i8 [[RETVAL]]
;
%1 = and i8 %a, 1
@@ -58,8 +55,7 @@ define i8 @select_icmp_eq_and_inv(i8 noundef %a, i8 %b) {
; CHECK-SAME: i8 noundef [[A:%.*]], i8 [[B:%.*]]) {
; CHECK-NEXT: [[TMP1:%.*]] = and i8 [[A]], 1
; CHECK-NEXT: [[CMP_NOT:%.*]] = icmp eq i8 [[TMP1]], 0
-; CHECK-NEXT: [[DIV:%.*]] = and i8 [[A]], -2
-; CHECK-NEXT: [[RETVAL:%.*]] = select i1 [[CMP_NOT]], i8 [[DIV]], i8 [[B]]
+; CHECK-NEXT: [[RETVAL:%.*]] = select i1 [[CMP_NOT]], i8 [[A]], i8 [[B]]
; CHECK-NEXT: ret i8 [[RETVAL]]
;
%1 = and i8 %a, 1
diff --git a/llvm/test/Transforms/InstCombine/select.ll b/llvm/test/Transforms/InstCombine/select.ll
index 1369be305ec13..1c7247ec6a8b3 100644
--- a/llvm/test/Transforms/InstCombine/select.ll
+++ b/llvm/test/Transforms/InstCombine/select.ll
@@ -2989,9 +2989,8 @@ define i8 @select_replacement_loop3(i32 noundef %x) {
define i16 @select_replacement_loop4(i16 noundef %p_12) {
; CHECK-LABEL: @select_replacement_loop4(
-; CHECK-NEXT: [[AND1:%.*]] = and i16 [[P_12:%.*]], 1
-; CHECK-NEXT: [[CMP21:%.*]] = icmp ult i16 [[P_12]], 2
-; CHECK-NEXT: [[AND3:%.*]] = select i1 [[CMP21]], i16 [[AND1]], i16 0
+; CHECK-NEXT: [[CMP21:%.*]] = icmp ult i16 [[P_12:%.*]], 2
+; CHECK-NEXT: [[AND3:%.*]] = select i1 [[CMP21]], i16 [[P_12]], i16 0
; CHECK-NEXT: ret i16 [[AND3]]
;
%cmp1 = icmp ult i16 %p_12, 2
@@ -4671,8 +4670,7 @@ define i8 @select_knownbits_simplify(i8 noundef %x) {
; CHECK-LABEL: @select_knownbits_simplify(
; CHECK-NEXT: [[X_LO:%.*]] = and i8 [[X:%.*]], 1
; CHECK-NEXT: [[CMP:%.*]] = icmp eq i8 [[X_LO]], 0
-; CHECK-NEXT: [[AND:%.*]] = and i8 [[X]], -2
-; CHECK-NEXT: [[RES:%.*]] = select i1 [[CMP]], i8 [[AND]], i8 0
+; CHECK-NEXT: [[RES:%.*]] = select i1 [[CMP]], i8 [[X]], i8 0
; CHECK-NEXT: ret i8 [[RES]]
;
%x.lo = and i8 %x, 1
@@ -4686,8 +4684,7 @@ define i8 @select_knownbits_simplify_nested(i8 noundef %x) {
; CHECK-LABEL: @select_knownbits_simplify_nested(
; CHECK-NEXT: [[X_LO:%.*]] = and i8 [[X:%.*]], 1
; CHECK-NEXT: [[CMP:%.*]] = icmp eq i8 [[X_LO]], 0
-; CHECK-NEXT: [[AND:%.*]] = and i8 [[X]], -2
-; CHECK-NEXT: [[MUL:%.*]] = mul i8 [[AND]], [[AND]]
+; CHECK-NEXT: [[MUL:%.*]] = mul i8 [[X]], [[X]]
; CHECK-NEXT: [[RES:%.*]] = select i1 [[CMP]], i8 [[MUL]], i8 0
; CHECK-NEXT: ret i8 [[RES]]
;
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