[llvm] [SCEV] Simplify SCEVExpr for PHI to SCEV for operand if operands are identical (PR #115945)
Akshay Deodhar via llvm-commits
llvm-commits at lists.llvm.org
Mon Nov 18 12:21:24 PST 2024
https://github.com/akshayrdeodhar updated https://github.com/llvm/llvm-project/pull/115945
>From ff9c1b86e79a9cf52279347fef9b73bc60ced4b7 Mon Sep 17 00:00:00 2001
From: Akshay Deodhar <adeodhar at nvidia.com>
Date: Wed, 30 Oct 2024 04:03:39 +0000
Subject: [PATCH 1/2] [SCEV] Simplify SCEVExpr for PHI to SCEV for operand if
operands are identical
---
llvm/include/llvm/Analysis/ScalarEvolution.h | 4 ++
llvm/lib/Analysis/ScalarEvolution.cpp | 34 ++++++++++++++
.../Analysis/ScalarEvolution/trip-count16.ll | 46 +++++++++++++++++++
3 files changed, 84 insertions(+)
create mode 100644 llvm/test/Analysis/ScalarEvolution/trip-count16.ll
diff --git a/llvm/include/llvm/Analysis/ScalarEvolution.h b/llvm/include/llvm/Analysis/ScalarEvolution.h
index 4b8cb3a39a86db..86f4cb92152836 100644
--- a/llvm/include/llvm/Analysis/ScalarEvolution.h
+++ b/llvm/include/llvm/Analysis/ScalarEvolution.h
@@ -1761,6 +1761,10 @@ class ScalarEvolution {
/// V.
const SCEV *getOperandsToCreate(Value *V, SmallVectorImpl<Value *> &Ops);
+ /// Returns SCEV for the first operand of a phi if all phi operands have
+ /// identical opcodes and operands
+ const SCEV *createNodeForPHIWithIdenticalOperands(PHINode *PN);
+
/// Provide the special handling we need to analyze PHI SCEVs.
const SCEV *createNodeForPHI(PHINode *PN);
diff --git a/llvm/lib/Analysis/ScalarEvolution.cpp b/llvm/lib/Analysis/ScalarEvolution.cpp
index b10811133770e1..3480dda484f333 100644
--- a/llvm/lib/Analysis/ScalarEvolution.cpp
+++ b/llvm/lib/Analysis/ScalarEvolution.cpp
@@ -6019,6 +6019,37 @@ const SCEV *ScalarEvolution::createNodeFromSelectLikePHI(PHINode *PN) {
return nullptr;
}
+// Returns SCEV for the first operand of a phi if all phi operands have
+// identical opcodes and operands
+// eg.
+// a: %add = %a + %b
+// br %c
+// b: %add1 = %a + %b
+// br %c
+// c: %phi = phi [%add, a], [%add1, b]
+// scev(%phi) => scev(%add)
+const SCEV *
+ScalarEvolution::createNodeForPHIWithIdenticalOperands(PHINode *PN) {
+ BinaryOperator *CommonInst = nullptr;
+ for (Value *Incoming : PN->incoming_values()) {
+ BinaryOperator *IncomingInst = dyn_cast<BinaryOperator>(Incoming);
+ if (CommonInst) {
+ if (!(IncomingInst && CommonInst->isIdenticalTo(IncomingInst))) {
+ // Not identical, give up
+ CommonInst = nullptr;
+ break;
+ }
+ } else if (IncomingInst) {
+ // Remember binary operator
+ CommonInst = IncomingInst;
+ } else {
+ // Not a binary operator, give up
+ return nullptr;
+ }
+ }
+ return CommonInst ? getSCEV(CommonInst) : nullptr;
+}
+
const SCEV *ScalarEvolution::createNodeForPHI(PHINode *PN) {
if (const SCEV *S = createAddRecFromPHI(PN))
return S;
@@ -6030,6 +6061,9 @@ const SCEV *ScalarEvolution::createNodeForPHI(PHINode *PN) {
/*UseInstrInfo=*/true, /*CanUseUndef=*/false}))
return getSCEV(V);
+ if (const SCEV *S = createNodeForPHIWithIdenticalOperands(PN))
+ return S;
+
if (const SCEV *S = createNodeFromSelectLikePHI(PN))
return S;
diff --git a/llvm/test/Analysis/ScalarEvolution/trip-count16.ll b/llvm/test/Analysis/ScalarEvolution/trip-count16.ll
new file mode 100644
index 00000000000000..2b267edb2438f9
--- /dev/null
+++ b/llvm/test/Analysis/ScalarEvolution/trip-count16.ll
@@ -0,0 +1,46 @@
+; NOTE: Assertions have been autogenerated by utils/update_analyze_test_checks.py UTC_ARGS: --version 5
+; RUN: opt < %s -disable-output "-passes=print<scalar-evolution>" 2>&1 | FileCheck %s
+define void @test(ptr %x, ptr %y) {
+; CHECK-LABEL: 'test'
+; CHECK-NEXT: Classifying expressions for: @test
+; CHECK-NEXT: %v1.0 = phi i32 [ 0, %entry ], [ %k.0, %if.end ]
+; CHECK-NEXT: --> {0,+,1}<nuw><nsw><%for.cond> U: [0,7) S: [0,7) Exits: 6 LoopDispositions: { %for.cond: Computable }
+; CHECK-NEXT: %add = add nsw i32 %v1.0, 1
+; CHECK-NEXT: --> {1,+,1}<nuw><nsw><%for.cond> U: [1,8) S: [1,8) Exits: 7 LoopDispositions: { %for.cond: Computable }
+; CHECK-NEXT: %add6 = add nsw i32 %v1.0, 1
+; CHECK-NEXT: --> {1,+,1}<nuw><nsw><%for.cond> U: [1,8) S: [1,8) Exits: 7 LoopDispositions: { %for.cond: Computable }
+; CHECK-NEXT: %k.0 = phi i32 [ %add, %if.then ], [ %add6, %if.else ]
+; CHECK-NEXT: --> {1,+,1}<nuw><nsw><%for.cond> U: [1,8) S: [1,8) Exits: 7 LoopDispositions: { %for.cond: Computable }
+; CHECK-NEXT: Determining loop execution counts for: @test
+; CHECK-NEXT: Loop %for.cond: backedge-taken count is i32 6
+; CHECK-NEXT: Loop %for.cond: constant max backedge-taken count is i32 6
+; CHECK-NEXT: Loop %for.cond: symbolic max backedge-taken count is i32 6
+; CHECK-NEXT: Loop %for.cond: Trip multiple is 7
+;
+entry:
+ br label %for.cond
+
+for.cond: ; preds = %6, %0
+ %v1.0 = phi i32 [ 0, %entry ], [ %k.0, %if.end ]
+ %cmp = icmp slt i32 %v1.0, 6
+ br i1 %cmp, label %for.body, label %exit
+
+for.body: ; preds = %1
+ %cmp3 = icmp slt i32 %v1.0, 2
+ br i1 %cmp3, label %if.then, label %if.else
+
+if.then: ; preds = %2
+ %add = add nsw i32 %v1.0, 1
+ br label %if.end
+
+if.else: ; preds = %2
+ %add6 = add nsw i32 %v1.0, 1
+ br label %if.end
+
+if.end: ; preds = %4, %3
+ %k.0 = phi i32 [ %add, %if.then ], [ %add6, %if.else ]
+ br label %for.cond
+
+exit: ; preds = %5
+ ret void
+}
>From 24e42625704f43f0632df7b17e2f437374cfae59 Mon Sep 17 00:00:00 2001
From: Akshay Deodhar <adeodhar at nvidia.com>
Date: Fri, 15 Nov 2024 22:36:01 +0000
Subject: [PATCH 2/2] address review comments
---
llvm/lib/Analysis/ScalarEvolution.cpp | 25 +++++++++++--------------
1 file changed, 11 insertions(+), 14 deletions(-)
diff --git a/llvm/lib/Analysis/ScalarEvolution.cpp b/llvm/lib/Analysis/ScalarEvolution.cpp
index 3480dda484f333..d18eb3a26b895a 100644
--- a/llvm/lib/Analysis/ScalarEvolution.cpp
+++ b/llvm/lib/Analysis/ScalarEvolution.cpp
@@ -6019,26 +6019,23 @@ const SCEV *ScalarEvolution::createNodeFromSelectLikePHI(PHINode *PN) {
return nullptr;
}
-// Returns SCEV for the first operand of a phi if all phi operands have
-// identical opcodes and operands
-// eg.
-// a: %add = %a + %b
-// br %c
-// b: %add1 = %a + %b
-// br %c
-// c: %phi = phi [%add, a], [%add1, b]
-// scev(%phi) => scev(%add)
+/// Returns SCEV for the first operand of a phi if all phi operands have
+/// identical opcodes and operands
+/// eg.
+/// a: %add = %a + %b
+/// br %c
+/// b: %add1 = %a + %b
+/// br %c
+/// c: %phi = phi [%add, a], [%add1, b]
+/// scev(%phi) => scev(%add)
const SCEV *
ScalarEvolution::createNodeForPHIWithIdenticalOperands(PHINode *PN) {
BinaryOperator *CommonInst = nullptr;
for (Value *Incoming : PN->incoming_values()) {
BinaryOperator *IncomingInst = dyn_cast<BinaryOperator>(Incoming);
if (CommonInst) {
- if (!(IncomingInst && CommonInst->isIdenticalTo(IncomingInst))) {
- // Not identical, give up
- CommonInst = nullptr;
- break;
- }
+ if (!(IncomingInst && CommonInst->isIdenticalTo(IncomingInst)))
+ return nullptr; // Not identical, give up
} else if (IncomingInst) {
// Remember binary operator
CommonInst = IncomingInst;
More information about the llvm-commits
mailing list