[llvm] Reland "[Transforms] LoopIdiomRecognize recognize strlen and wcslen #108985" (PR #132572)
via llvm-commits
llvm-commits at lists.llvm.org
Sat Mar 22 16:26:01 PDT 2025
llvmbot wrote:
<!--LLVM PR SUMMARY COMMENT-->
@llvm/pr-subscribers-llvm-transforms
Author: Henry Jiang (mustartt)
<details>
<summary>Changes</summary>
Reland https://github.com/llvm/llvm-project/pull/108985
In this patch, also add `strlen` and `wcslen` to the common idiom names list so that functions named `strlen` or `wcslen` does not get transformed.
---
Patch is 61.34 KiB, truncated to 20.00 KiB below, full version: https://github.com/llvm/llvm-project/pull/132572.diff
9 Files Affected:
- (modified) llvm/include/llvm/Transforms/Scalar/LoopIdiomRecognize.h (+6)
- (modified) llvm/include/llvm/Transforms/Utils/BuildLibCalls.h (+6)
- (modified) llvm/lib/Transforms/Scalar/LoopIdiomRecognize.cpp (+293-5)
- (modified) llvm/lib/Transforms/Utils/BuildLibCalls.cpp (+9)
- (added) llvm/test/Transforms/LoopIdiom/strlen-noidiom.ll (+64)
- (added) llvm/test/Transforms/LoopIdiom/strlen-not-emittable.ll (+66)
- (added) llvm/test/Transforms/LoopIdiom/strlen.ll (+614)
- (added) llvm/test/Transforms/LoopIdiom/wcslen16.ll (+126)
- (added) llvm/test/Transforms/LoopIdiom/wcslen32.ll (+134)
``````````diff
diff --git a/llvm/include/llvm/Transforms/Scalar/LoopIdiomRecognize.h b/llvm/include/llvm/Transforms/Scalar/LoopIdiomRecognize.h
index 0c6406d861851..241a3fc109360 100644
--- a/llvm/include/llvm/Transforms/Scalar/LoopIdiomRecognize.h
+++ b/llvm/include/llvm/Transforms/Scalar/LoopIdiomRecognize.h
@@ -34,6 +34,12 @@ struct DisableLIRP {
/// When true, Memcpy is disabled.
static bool Memcpy;
+
+ /// When true, Strlen is disabled.
+ static bool Strlen;
+
+ /// When true, Wcslen is disabled.
+ static bool Wcslen;
};
/// Performs Loop Idiom Recognize Pass.
diff --git a/llvm/include/llvm/Transforms/Utils/BuildLibCalls.h b/llvm/include/llvm/Transforms/Utils/BuildLibCalls.h
index a8fb38e726004..50f695dbe6c07 100644
--- a/llvm/include/llvm/Transforms/Utils/BuildLibCalls.h
+++ b/llvm/include/llvm/Transforms/Utils/BuildLibCalls.h
@@ -93,6 +93,12 @@ namespace llvm {
Value *emitStrLen(Value *Ptr, IRBuilderBase &B, const DataLayout &DL,
const TargetLibraryInfo *TLI);
+ /// Emit a call to the wcslen function to the builder, for the specified
+ /// pointer. Ptr is required to be some pointer type, and the return value has
+ /// 'size_t' type.
+ Value *emitWcsLen(Value *Ptr, IRBuilderBase &B, const DataLayout &DL,
+ const TargetLibraryInfo *TLI);
+
/// Emit a call to the strdup function to the builder, for the specified
/// pointer. Ptr is required to be some pointer type, and the return value has
/// 'i8*' type.
diff --git a/llvm/lib/Transforms/Scalar/LoopIdiomRecognize.cpp b/llvm/lib/Transforms/Scalar/LoopIdiomRecognize.cpp
index 8dc7f325f6262..4940dd8c47dde 100644
--- a/llvm/lib/Transforms/Scalar/LoopIdiomRecognize.cpp
+++ b/llvm/lib/Transforms/Scalar/LoopIdiomRecognize.cpp
@@ -20,8 +20,7 @@
//
// TODO List:
//
-// Future loop memory idioms to recognize:
-// memcmp, strlen, etc.
+// Future loop memory idioms to recognize: memcmp, etc.
//
// This could recognize common matrix multiplies and dot product idioms and
// replace them with calls to BLAS (if linked in??).
@@ -33,6 +32,7 @@
#include "llvm/ADT/ArrayRef.h"
#include "llvm/ADT/DenseMap.h"
#include "llvm/ADT/MapVector.h"
+#include "llvm/ADT/STLExtras.h"
#include "llvm/ADT/SetVector.h"
#include "llvm/ADT/SmallPtrSet.h"
#include "llvm/ADT/SmallVector.h"
@@ -97,6 +97,7 @@ using namespace llvm;
STATISTIC(NumMemSet, "Number of memset's formed from loop stores");
STATISTIC(NumMemCpy, "Number of memcpy's formed from loop load+stores");
STATISTIC(NumMemMove, "Number of memmove's formed from loop load+stores");
+STATISTIC(NumStrLen, "Number of strlen's and wcslen's formed from loop loads");
STATISTIC(
NumShiftUntilBitTest,
"Number of uncountable loops recognized as 'shift until bitttest' idiom");
@@ -126,6 +127,22 @@ static cl::opt<bool, true>
cl::location(DisableLIRP::Memcpy), cl::init(false),
cl::ReallyHidden);
+bool DisableLIRP::Strlen;
+static cl::opt<bool, true>
+ DisableLIRPStrlen("disable-loop-idiom-strlen",
+ cl::desc("Proceed with loop idiom recognize pass, but do "
+ "not convert loop(s) to strlen."),
+ cl::location(DisableLIRP::Strlen), cl::init(false),
+ cl::ReallyHidden);
+
+bool DisableLIRP::Wcslen;
+static cl::opt<bool, true>
+ EnableLIRPWcslen("disable-loop-idiom-wcslen",
+ cl::desc("Proceed with loop idiom recognize pass, "
+ "enable conversion of loop(s) to wcslen."),
+ cl::location(DisableLIRP::Wcslen), cl::init(false),
+ cl::ReallyHidden);
+
static cl::opt<bool> UseLIRCodeSizeHeurs(
"use-lir-code-size-heurs",
cl::desc("Use loop idiom recognition code size heuristics when compiling "
@@ -246,6 +263,7 @@ class LoopIdiomRecognize {
bool recognizeShiftUntilBitTest();
bool recognizeShiftUntilZero();
+ bool recognizeAndInsertStrLen();
/// @}
};
@@ -295,7 +313,8 @@ bool LoopIdiomRecognize::runOnLoop(Loop *L) {
// Disable loop idiom recognition if the function's name is a common idiom.
StringRef Name = L->getHeader()->getParent()->getName();
- if (Name == "memset" || Name == "memcpy")
+ if (Name == "memset" || Name == "memcpy" || Name == "strlen" ||
+ Name == "wcslen")
return false;
// Determine if code size heuristics need to be applied.
@@ -1494,7 +1513,7 @@ bool LoopIdiomRecognize::runOnNoncountableLoop() {
return recognizePopcount() || recognizeAndInsertFFS() ||
recognizeShiftUntilBitTest() || recognizeShiftUntilZero() ||
- recognizeShiftUntilLessThan();
+ recognizeShiftUntilLessThan() || recognizeAndInsertStrLen();
}
/// Check if the given conditional branch is based on the comparison between
@@ -1512,7 +1531,7 @@ static Value *matchCondition(BranchInst *BI, BasicBlock *LoopEntry,
if (!Cond)
return nullptr;
- ConstantInt *CmpZero = dyn_cast<ConstantInt>(Cond->getOperand(1));
+ auto *CmpZero = dyn_cast<ConstantInt>(Cond->getOperand(1));
if (!CmpZero || !CmpZero->isZero())
return nullptr;
@@ -1529,6 +1548,275 @@ static Value *matchCondition(BranchInst *BI, BasicBlock *LoopEntry,
return nullptr;
}
+namespace {
+
+class StrlenVerifier {
+public:
+ explicit StrlenVerifier(const Loop *CurLoop, ScalarEvolution *SE,
+ const TargetLibraryInfo *TLI)
+ : CurLoop(CurLoop), SE(SE), TLI(TLI) {}
+
+ bool isValidStrlenIdiom() {
+ // Give up if the loop has multiple blocks, multiple backedges, or
+ // multiple exit blocks
+ if (CurLoop->getNumBackEdges() != 1 || CurLoop->getNumBlocks() != 1 ||
+ !CurLoop->getUniqueExitBlock())
+ return false;
+
+ // It should have a preheader and a branch instruction.
+ BasicBlock *Preheader = CurLoop->getLoopPreheader();
+ if (!Preheader)
+ return false;
+
+ BranchInst *EntryBI = dyn_cast<BranchInst>(Preheader->getTerminator());
+ if (!EntryBI)
+ return false;
+
+ // The loop exit must be conditioned on an icmp with 0 the null terminator.
+ // The icmp operand has to be a load on some SSA reg that increments
+ // by 1 in the loop.
+ BasicBlock *LoopBody = *CurLoop->block_begin();
+
+ // Skip if the body is too big as it most likely is not a strlen idiom.
+ if (!LoopBody || LoopBody->size() >= 15)
+ return false;
+
+ BranchInst *LoopTerm = dyn_cast<BranchInst>(LoopBody->getTerminator());
+ Value *LoopCond = matchCondition(LoopTerm, LoopBody);
+ if (!LoopCond)
+ return false;
+
+ LoadInst *LoopLoad = dyn_cast<LoadInst>(LoopCond);
+ if (!LoopLoad || LoopLoad->getPointerAddressSpace() != 0)
+ return false;
+
+ OperandType = LoopLoad->getType();
+ if (!OperandType || !OperandType->isIntegerTy())
+ return false;
+
+ // See if the pointer expression is an AddRec with constant step a of form
+ // ({n,+,a}) where a is the width of the char type.
+ Value *IncPtr = LoopLoad->getPointerOperand();
+ const SCEVAddRecExpr *LoadEv =
+ dyn_cast<SCEVAddRecExpr>(SE->getSCEV(IncPtr));
+ if (!LoadEv || LoadEv->getLoop() != CurLoop || !LoadEv->isAffine())
+ return false;
+ LoadBaseEv = LoadEv->getStart();
+
+ LLVM_DEBUG(dbgs() << "pointer load scev: " << *LoadEv << "\n");
+
+ const SCEVConstant *Step =
+ dyn_cast<SCEVConstant>(LoadEv->getStepRecurrence(*SE));
+ if (!Step)
+ return false;
+
+ unsigned StepSize = 0;
+ StepSizeCI = dyn_cast<ConstantInt>(Step->getValue());
+ if (!StepSizeCI)
+ return false;
+ StepSize = StepSizeCI->getZExtValue();
+
+ // Verify that StepSize is consistent with platform char width.
+ OpWidth = OperandType->getIntegerBitWidth();
+ unsigned WcharSize = TLI->getWCharSize(*LoopLoad->getModule());
+ if (OpWidth != StepSize * 8)
+ return false;
+ if (OpWidth != 8 && OpWidth != 16 && OpWidth != 32)
+ return false;
+ if (OpWidth >= 16)
+ if (OpWidth != WcharSize * 8)
+ return false;
+
+ // Scan every instruction in the loop to ensure there are no side effects.
+ for (Instruction &I : *LoopBody)
+ if (I.mayHaveSideEffects())
+ return false;
+
+ BasicBlock *LoopExitBB = CurLoop->getExitBlock();
+ if (!LoopExitBB)
+ return false;
+
+ for (PHINode &PN : LoopExitBB->phis()) {
+ if (!SE->isSCEVable(PN.getType()))
+ return false;
+
+ const SCEV *Ev = SE->getSCEV(&PN);
+ if (!Ev)
+ return false;
+
+ 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
+ // SCEVExpander materialize the loop output.
+ const SCEVAddRecExpr *AddRecEv = dyn_cast<SCEVAddRecExpr>(Ev);
+ if (!AddRecEv || !AddRecEv->isAffine())
+ return false;
+
+ // We only want RecAddExpr with recurrence step that is constant. This
+ // is good enough for all the idioms we want to recognize. Later we expand
+ // and materialize the recurrence as {base,+,a} -> (base + a * strlen)
+ if (!dyn_cast<SCEVConstant>(AddRecEv->getStepRecurrence(*SE)))
+ return false;
+ }
+
+ return true;
+ }
+
+public:
+ const Loop *CurLoop;
+ ScalarEvolution *SE;
+ const TargetLibraryInfo *TLI;
+
+ unsigned OpWidth;
+ ConstantInt *StepSizeCI;
+ const SCEV *LoadBaseEv;
+ Type *OperandType;
+};
+
+} // namespace
+
+/// The Strlen Idiom we are trying to detect has the following structure
+///
+/// preheader:
+/// ...
+/// br label %body, ...
+///
+/// body:
+/// ... ; %0 is incremented by a gep
+/// %1 = load i8, ptr %0, align 1
+/// %2 = icmp eq i8 %1, 0
+/// br i1 %2, label %exit, label %body
+///
+/// exit:
+/// %lcssa = phi [%0, %body], ...
+///
+/// We expect the strlen idiom to have a load of a character type that
+/// is compared against '\0', and such load pointer operand must have scev
+/// expression of the form {%str,+,c} where c is a ConstantInt of the
+/// appropiate character width for the idiom, and %str is the base of the string
+/// And, that all lcssa phis have the form {...,+,n} where n is a constant,
+///
+/// When transforming the output of the strlen idiom, the lccsa phi are
+/// expanded using SCEVExpander as {base scev,+,a} -> (base scev + a * strlen)
+/// and all subsequent uses are replaced. For example,
+///
+/// \code{.c}
+/// const char* base = str;
+/// while (*str != '\0')
+/// ++str;
+/// size_t result = str - base;
+/// \endcode
+///
+/// will be transformed as follows: The idiom will be replaced by a strlen
+/// computation to compute the address of the null terminator of the string.
+///
+/// \code{.c}
+/// const char* base = str;
+/// const char* end = base + strlen(str);
+/// size_t result = end - base;
+/// \endcode
+///
+/// In the case we index by an induction variable, as long as the induction
+/// variable has a constant int increment, we can replace all such indvars
+/// with the closed form computation of strlen
+///
+/// \code{.c}
+/// size_t i = 0;
+/// while (str[i] != '\0')
+/// ++i;
+/// size_t result = i;
+/// \endcode
+///
+/// Will be replaced by
+///
+/// \code{.c}
+/// size_t i = 0 + strlen(str);
+/// size_t result = i;
+/// \endcode
+///
+bool LoopIdiomRecognize::recognizeAndInsertStrLen() {
+ if (DisableLIRP::All)
+ return false;
+
+ StrlenVerifier Verifier(CurLoop, SE, TLI);
+
+ if (!Verifier.isValidStrlenIdiom())
+ return false;
+
+ 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");
+ Value *MaterialzedBase = Expander.expandCodeFor(
+ Verifier.LoadBaseEv, Verifier.LoadBaseEv->getType(),
+ Builder.GetInsertPoint());
+
+ Value *StrLenFunc = nullptr;
+ if (Verifier.OpWidth == 8) {
+ StrLenFunc = emitStrLen(MaterialzedBase, Builder, *DL, TLI);
+ } else {
+ StrLenFunc = emitWcsLen(MaterialzedBase, Builder, *DL, TLI);
+ }
+ assert(StrLenFunc && "Failed to emit strlen function.");
+
+ const SCEV *StrlenEv = SE->getSCEV(StrLenFunc);
+ SmallVector<PHINode *, 4> Cleanup;
+ for (PHINode &PN : LoopExitBB->phis()) {
+ // We can now materialize the loop output as all phi have scev {base,+,a}.
+ // We expand the phi as:
+ // %strlen = call i64 @strlen(%str)
+ // %phi.new = base expression + step * %strlen
+ const SCEV *Ev = SE->getSCEV(&PN);
+ const SCEVAddRecExpr *AddRecEv = dyn_cast<SCEVAddRecExpr>(Ev);
+ const SCEVConstant *Step =
+ dyn_cast<SCEVConstant>(AddRecEv->getStepRecurrence(*SE));
+ const SCEV *Base = AddRecEv->getStart();
+
+ // It is safe to truncate to base since if base is narrower than size_t
+ // the equivalent user code will have to truncate anyways.
+ const SCEV *NewEv = SE->getAddExpr(
+ Base, SE->getMulExpr(Step, SE->getTruncateOrSignExtend(
+ StrlenEv, Base->getType())));
+
+ Value *MaterializedPHI = Expander.expandCodeFor(NewEv, NewEv->getType(),
+ Builder.GetInsertPoint());
+ Expander.clear();
+ PN.replaceAllUsesWith(MaterializedPHI);
+ Cleanup.push_back(&PN);
+ }
+
+ // All LCSSA Loop Phi are dead, the left over dead loop body can be cleaned
+ // up by later passes
+ for (PHINode *PN : Cleanup)
+ RecursivelyDeleteDeadPHINode(PN);
+ SE->forgetLoop(CurLoop);
+
+ ++NumStrLen;
+ LLVM_DEBUG(dbgs() << " Formed strlen idiom: " << *StrLenFunc << "\n");
+ ORE.emit([&]() {
+ return OptimizationRemark(DEBUG_TYPE, "recognizeAndInsertStrLen",
+ CurLoop->getStartLoc(), Preheader)
+ << "Transformed " << StrLenFunc->getName() << " loop idiom";
+ });
+
+ return true;
+}
+
/// Check if the given conditional branch is based on an unsigned less-than
/// comparison between a variable and a constant, and if the comparison is false
/// the control yields to the loop entry. If the branch matches the behaviour,
diff --git a/llvm/lib/Transforms/Utils/BuildLibCalls.cpp b/llvm/lib/Transforms/Utils/BuildLibCalls.cpp
index 2301be6977cef..24eefc91117b4 100644
--- a/llvm/lib/Transforms/Utils/BuildLibCalls.cpp
+++ b/llvm/lib/Transforms/Utils/BuildLibCalls.cpp
@@ -1582,6 +1582,15 @@ Value *llvm::emitStrLen(Value *Ptr, IRBuilderBase &B, const DataLayout &DL,
return emitLibCall(LibFunc_strlen, SizeTTy, CharPtrTy, Ptr, B, TLI);
}
+Value *llvm::emitWcsLen(Value *Ptr, IRBuilderBase &B, const DataLayout &DL,
+ const TargetLibraryInfo *TLI) {
+ assert(Ptr && Ptr->getType()->isPointerTy() &&
+ "Argument to wcslen intrinsic must be a pointer.");
+ Type *PtrTy = B.getPtrTy();
+ Type *SizeTTy = getSizeTTy(B, TLI);
+ return emitLibCall(LibFunc_wcslen, SizeTTy, PtrTy, Ptr, B, TLI);
+}
+
Value *llvm::emitStrDup(Value *Ptr, IRBuilderBase &B,
const TargetLibraryInfo *TLI) {
Type *CharPtrTy = B.getPtrTy();
diff --git a/llvm/test/Transforms/LoopIdiom/strlen-noidiom.ll b/llvm/test/Transforms/LoopIdiom/strlen-noidiom.ll
new file mode 100644
index 0000000000000..498ec52ed26ee
--- /dev/null
+++ b/llvm/test/Transforms/LoopIdiom/strlen-noidiom.ll
@@ -0,0 +1,64 @@
+; 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"
+
+; CHECK-LABEL: @strlen(
+; CHECK-NOT: call{{.*}} strlen
+; CHECK-LABEL: @wcslen(
+; CHECK-NOT: call{{.*}} wcslen
+
+define i64 @strlen(ptr %str) {
+entry:
+ br label %while.cond
+
+while.cond:
+ %str.addr.0 = phi ptr [ %str, %entry ], [ %incdec.ptr, %while.cond ]
+ %0 = load i8, ptr %str.addr.0, align 1
+ %cmp.not = icmp eq i8 %0, 0
+ %incdec.ptr = getelementptr i8, ptr %str.addr.0, i64 1
+ br i1 %cmp.not, label %while.end, label %while.cond
+
+while.end:
+ %sub.ptr.lhs.cast = ptrtoint ptr %str.addr.0 to i64
+ %sub.ptr.rhs.cast = ptrtoint ptr %str to i64
+ %sub.ptr.sub = sub i64 %sub.ptr.lhs.cast, %sub.ptr.rhs.cast
+ ret i64 %sub.ptr.sub
+}
+
+define i64 @wcslen(ptr %src) {
+entry:
+ %cmp = icmp eq ptr %src, null
+ br i1 %cmp, label %return, label %lor.lhs.false
+
+lor.lhs.false: ; preds = %entry
+ %0 = load i32, ptr %src, align 4
+ %cmp1 = icmp eq i32 %0, 0
+ br i1 %cmp1, label %return, label %while.cond.preheader
+
+while.cond.preheader: ; preds = %lor.lhs.false
+ br label %while.cond
+
+while.cond: ; preds = %while.cond.preheader, %while.cond
+ %src.pn = phi ptr [ %curr.0, %while.cond ], [ %src, %while.cond.preheader ]
+ %curr.0 = getelementptr inbounds i8, ptr %src.pn, i64 4
+ %1 = load i32, ptr %curr.0, align 4
+ %tobool.not = icmp eq i32 %1, 0
+ br i1 %tobool.not, label %while.end, label %while.cond
+
+while.end: ; preds = %while.cond
+ %curr.0.lcssa = phi ptr [ %curr.0, %while.cond ]
+ %sub.ptr.lhs.cast = ptrtoint ptr %curr.0.lcssa to i64
+ %sub.ptr.rhs.cast = ptrtoint ptr %src to i64
+ %sub.ptr.sub = sub i64 %sub.ptr.lhs.cast, %sub.ptr.rhs.cast
+ %sub.ptr.div = ashr exact i64 %sub.ptr.sub, 2
+ br label %return
+
+return: ; preds = %entry, %lor.lhs.false, %while.end
+ %retval.0 = phi i64 [ %sub.ptr.div, %while.end ], [ 0, %lor.lhs.false ], [ 0, %entry ]
+ ret i64 %retval.0
+}
+
+
+!llvm.module.flags = !{!0}
+!0 = !{i32 1, !"wchar_size", i32 4}
diff --git a/llvm/test/Transforms/LoopIdiom/strlen-not-emittable.ll b/llvm/test/Transforms/LoopIdiom/strlen-not-emittable.ll
new file mode 100644
index 0000000000000..00fbe89846a30
--- /dev/null
+++ b/llvm/test/Transforms/LoopIdiom/strlen-not-emittable.ll
@@ -0,0 +1,66 @@
+; 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"
+
+; invalid libcall prototype
+declare void @strlen(i32)
+declare void @wcslen(i32)
+
+define i64 @valid_wcslen32(ptr %src) {
+; CHECK-LABEL: valid_wcslen32
+; CHECK-NOT: call {{.*}} @wcslen
+entry:
+ %cmp = icmp eq ptr %src, null
+ br i1 %cmp, label %return, label %lor.lhs.false
+
+lor.lhs.false: ; preds = %entry
+ %0 = load i32, ptr %src, align 4
+ %cmp1 = icmp eq i32 %0, 0
+ br i1 %cmp1, label %return, label %while.cond.preheader
+
+while.cond.preheader: ; preds = %lor.lhs.false
+ br label %while.cond
+
+while.cond: ; preds = %while.cond.preheader, %while.cond
+ %src.pn = phi ptr [ %curr.0, %while.cond ], [ %src, %while.cond.preheader ]
+ %curr.0 = getelementptr inbounds i8, ptr %src.pn, i64 4
+ %1 = load i32, ptr %curr.0, align 4
+ %tobool.not = icmp eq i32 %1, 0
+ br i1 %tobool.not, label %while.end, label %while.cond
+
+while.end: ; preds = %while.cond
+ %curr.0.lcssa = phi ptr [ %curr.0, %while.cond ]
+ %sub.ptr.lhs.cast = ptrtoint ptr %curr.0.lcssa to i64
+ %sub.ptr.rhs.cast = ptrtoint ptr %src to i64
+ %sub.ptr.sub = sub i64 %sub.ptr.lhs.cast, %sub.ptr.rhs.cast
+ %sub.ptr.div = ashr exact i64 %sub.ptr.sub, 2
+ br label %return
+
+return: ; preds = %entry, %lor.lhs.false, %while.end
+ %retval.0 = phi i64 [ %sub.ptr.div, %while.end ], [ 0, %lor.lhs.false ], [ 0, %entry ]
+ ret i64 %retval.0
+}
+
+define i64 @valid_strlen(ptr %str) {
+; CHECK-LABEL: valid_strlen
+; CHECK-NOT: call {{.*}} @strlen
+entry:
+ br label %while.cond
+
+while.cond:
+ %str.addr.0 = phi ptr [ %str, %entry ], [ %incdec.ptr, %while.cond ]
+ %0 = load i8, ptr %str.addr.0, align 1
+ %cmp.not = icmp ...
[truncated]
``````````
</details>
https://github.com/llvm/llvm-project/pull/132572
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