[llvm] 82c93b6 - [SCEV] Simplify SCEVExpr for PHI to SCEV for operand if operands are identical (#115945)
via llvm-commits
llvm-commits at lists.llvm.org
Fri Dec 6 01:56:49 PST 2024
Author: Akshay Deodhar
Date: 2024-12-06T15:26:45+05:30
New Revision: 82c93b6f19bf9db75ac6e4100b9f1b4f2a7df67f
URL: https://github.com/llvm/llvm-project/commit/82c93b6f19bf9db75ac6e4100b9f1b4f2a7df67f
DIFF: https://github.com/llvm/llvm-project/commit/82c93b6f19bf9db75ac6e4100b9f1b4f2a7df67f.diff
LOG: [SCEV] Simplify SCEVExpr for PHI to SCEV for operand if operands are identical (#115945)
Helps SCEV analyze some special phi nodes, allowing the computation of
loop trip count in cases like the following:
https://godbolt.org/z/xGs1d81TW
Added:
llvm/test/Analysis/ScalarEvolution/trip-count-phi-increment.ll
Modified:
llvm/include/llvm/Analysis/ScalarEvolution.h
llvm/lib/Analysis/ScalarEvolution.cpp
Removed:
################################################################################
diff --git a/llvm/include/llvm/Analysis/ScalarEvolution.h b/llvm/include/llvm/Analysis/ScalarEvolution.h
index b20c6a13cb6bd7..de74524c4b6fe4 100644
--- a/llvm/include/llvm/Analysis/ScalarEvolution.h
+++ b/llvm/include/llvm/Analysis/ScalarEvolution.h
@@ -1780,6 +1780,10 @@ 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 882e938e69c0c2..cad10486cbf3fa 100644
--- a/llvm/lib/Analysis/ScalarEvolution.cpp
+++ b/llvm/lib/Analysis/ScalarEvolution.cpp
@@ -6019,6 +6019,42 @@ 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;
+ // Check if instructions are identical.
+ for (Value *Incoming : PN->incoming_values()) {
+ auto *IncomingInst = dyn_cast<BinaryOperator>(Incoming);
+ if (!IncomingInst)
+ return nullptr;
+ if (CommonInst) {
+ if (!CommonInst->isIdenticalToWhenDefined(IncomingInst))
+ return nullptr; // Not identical, give up
+ } else {
+ // Remember binary operator
+ CommonInst = IncomingInst;
+ }
+ }
+ if (!CommonInst)
+ return nullptr;
+
+ // Check if SCEV exprs for instructions are identical.
+ const SCEV *CommonSCEV = getSCEV(CommonInst);
+ bool SCEVExprsIdentical =
+ all_of(drop_begin(PN->incoming_values()),
+ [this, CommonSCEV](Value *V) { return CommonSCEV == getSCEV(V); });
+ return SCEVExprsIdentical ? CommonSCEV : nullptr;
+}
+
const SCEV *ScalarEvolution::createNodeForPHI(PHINode *PN) {
if (const SCEV *S = createAddRecFromPHI(PN))
return S;
@@ -6030,6 +6066,9 @@ 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-count-phi-increment.ll b/llvm/test/Analysis/ScalarEvolution/trip-count-phi-increment.ll
new file mode 100644
index 00000000000000..db284b263d068c
--- /dev/null
+++ b/llvm/test/Analysis/ScalarEvolution/trip-count-phi-increment.ll
@@ -0,0 +1,92 @@
+; 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 @test1(ptr %x, ptr %y) {
+; CHECK-LABEL: 'test1'
+; CHECK-NEXT: Classifying expressions for: @test1
+; 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: @test1
+; 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
+}
+
+define void @test2(ptr %x, ptr %y) {
+; CHECK-LABEL: 'test2'
+; CHECK-NEXT: Classifying expressions for: @test2
+; 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 nuw 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: @test2
+; 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 nuw 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
+}
+
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