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[Transform] Clean up strlen loop idiom #132421

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Merged
merged 3 commits into from
Mar 21, 2025
Merged

[Transform] Clean up strlen loop idiom #132421

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7f26c0f
bail out before modifing cfg
mustartt Mar 21, 2025
5316f36
remove verify pass
mustartt Mar 21, 2025
9b4df5c
use auto for cmp
mustartt Mar 21, 2025
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45 changes: 16 additions & 29 deletions llvm/lib/Transforms/Scalar/LoopIdiomRecognize.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -1515,16 +1515,6 @@ bool LoopIdiomRecognize::runOnNoncountableLoop() {
recognizeShiftUntilLessThan() || recognizeAndInsertStrLen();
}

/// Check if a Value is either a nullptr or a constant int zero
static bool isZeroConstant(const Value *Val) {
if (isa<ConstantPointerNull>(Val))
return true;
const ConstantInt *CmpZero = dyn_cast<ConstantInt>(Val);
if (!CmpZero || !CmpZero->isZero())
return false;
return true;
}

/// Check if the given conditional branch is based on the comparison between
/// a variable and zero, and if the variable is non-zero or zero (JmpOnZero is
/// true), the control yields to the loop entry. If the branch matches the
Expand All @@ -1540,7 +1530,8 @@ static Value *matchCondition(BranchInst *BI, BasicBlock *LoopEntry,
if (!Cond)
return nullptr;

if (!isZeroConstant(Cond->getOperand(1)))
auto *CmpZero = dyn_cast<ConstantInt>(Cond->getOperand(1));
if (!CmpZero || !CmpZero->isZero())
return nullptr;

BasicBlock *TrueSucc = BI->getSuccessor(0);
Expand Down Expand Up @@ -1611,11 +1602,7 @@ class StrlenVerifier {
return false;
LoadBaseEv = LoadEv->getStart();

LLVM_DEBUG({
dbgs() << "pointer load scev: ";
LoadEv->print(outs());
dbgs() << "\n";
});
LLVM_DEBUG(dbgs() << "pointer load scev: " << *LoadEv << "\n");

const SCEVConstant *Step =
dyn_cast<SCEVConstant>(LoadEv->getStepRecurrence(*SE));
Expand Down Expand Up @@ -1656,11 +1643,7 @@ class StrlenVerifier {
if (!Ev)
return false;

LLVM_DEBUG({
dbgs() << "loop exit phi scev: ";
Ev->print(dbgs());
dbgs() << "\n";
});
LLVM_DEBUG(dbgs() << "loop exit phi scev: " << *Ev << "\n");

// Since we verified that the loop trip count will be a valid strlen
// idiom, we can expand all lcssa phi with {n,+,1} as (n + strlen) and use
Expand Down Expand Up @@ -1763,6 +1746,18 @@ bool LoopIdiomRecognize::recognizeAndInsertStrLen() {
BasicBlock *Preheader = CurLoop->getLoopPreheader();
BasicBlock *LoopExitBB = CurLoop->getExitBlock();

if (Verifier.OpWidth == 8) {
if (DisableLIRP::Strlen)
return false;
if (!isLibFuncEmittable(Preheader->getModule(), TLI, LibFunc_strlen))
return false;
} else {
if (DisableLIRP::Wcslen)
return false;
if (!isLibFuncEmittable(Preheader->getModule(), TLI, LibFunc_wcslen))
return false;
}

IRBuilder<> Builder(Preheader->getTerminator());
SCEVExpander Expander(*SE, Preheader->getModule()->getDataLayout(),
"strlen_idiom");
Expand All @@ -1772,16 +1767,8 @@ bool LoopIdiomRecognize::recognizeAndInsertStrLen() {

Value *StrLenFunc = nullptr;
if (Verifier.OpWidth == 8) {
if (DisableLIRP::Strlen)
return false;
if (!isLibFuncEmittable(Preheader->getModule(), TLI, LibFunc_strlen))
return false;
StrLenFunc = emitStrLen(MaterialzedBase, Builder, *DL, TLI);
} else {
if (DisableLIRP::Wcslen)
return false;
if (!isLibFuncEmittable(Preheader->getModule(), TLI, LibFunc_wcslen))
return false;
StrLenFunc = emitWcsLen(MaterialzedBase, Builder, *DL, TLI);
}
assert(StrLenFunc && "Failed to emit strlen function.");
Expand Down
2 changes: 1 addition & 1 deletion llvm/test/Transforms/LoopIdiom/strlen-not-emittable.ll
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Original file line number Diff line number Diff line change
@@ -1,4 +1,4 @@
; RUN: opt -passes='loop(loop-idiom),verify' < %s -S | FileCheck %s
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@maryammo maryammo Mar 21, 2025

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Why removing the verify?

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@mustartt mustartt Mar 21, 2025 •
edited
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Its redundant:
#131412 (comment)

I also verified that verify is already scheduled at the end of the pipeline.

; RUN: opt -passes='loop(loop-idiom)' < %s -S | FileCheck %s

target datalayout = "e-m:e-p270:32:32-p271:32:32-p272:64:64-i64:64-i128:128-f80:128-n8:16:32:64-S128"
target triple = "x86_64-unknown-linux-gnu"
Expand Down
2 changes: 1 addition & 1 deletion llvm/test/Transforms/LoopIdiom/strlen.ll
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Original file line number Diff line number Diff line change
@@ -1,5 +1,5 @@
; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --version 5
; RUN: opt -passes='loop(loop-idiom),verify' < %s -S | FileCheck %s
; RUN: opt -passes='loop(loop-idiom)' < %s -S | FileCheck %s

declare void @other()
declare void @use(ptr)
Expand Down
2 changes: 1 addition & 1 deletion llvm/test/Transforms/LoopIdiom/wcslen16.ll
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Original file line number Diff line number Diff line change
@@ -1,5 +1,5 @@
; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --version 5
; RUN: opt -passes='loop(loop-idiom),verify' < %s -S | FileCheck %s
; RUN: opt -passes='loop(loop-idiom)' < %s -S | FileCheck %s

target datalayout = "e-m:e-p270:32:32-p271:32:32-p272:64:64-i64:64-i128:128-f80:128-n8:16:32:64-S128"
target triple = "x86_64-unknown-linux-gnu"
Expand Down
2 changes: 1 addition & 1 deletion llvm/test/Transforms/LoopIdiom/wcslen32.ll
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Original file line number Diff line number Diff line change
@@ -1,5 +1,5 @@
; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --version 5
; RUN: opt -passes='loop(loop-idiom),verify' < %s -S | FileCheck %s
; RUN: opt -passes='loop(loop-idiom)' < %s -S | FileCheck %s

target datalayout = "e-m:e-p270:32:32-p271:32:32-p272:64:64-i64:64-i128:128-f80:128-n8:16:32:64-S128"
target triple = "x86_64-unknown-linux-gnu"
Expand Down
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