dont transform idiom named strlen

Author: mustartt

llvm/lib/Transforms/Scalar/LoopIdiomRecognize.cpp

@@ -313,7 +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.

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}