Add ArgMemOnly attribute to strlen and wcslen, i.e. they only read memory (string) passed to them.

[trentxintong]

Summary

This allows strlen to be moved out of the loop in case its argument is
not modified in the loop in LICM.

[sanjoy]

Generally looks good, but the test isn't testing anything.

test/Transforms/LICM/strlen.ll

3

You're not running this through FileCheck at all. Look at the other LICM tests.

[trentxintong]

Address Comments

[sanjoy]

lgtm

test/Transforms/LICM/strlen.ll

16

Also check that #0 does, in fact, correspond to strlen.

[davide]

Fair enough.

[trentxintong]

Address comments

lib/Transforms/Utils/BuildLibCalls.cpp

if (!(TLI.getLibFunc(F, TheLibFunc) && TLI.has(TheLibFunc)))
     return false;
 
   bool Changed = false;
   switch (TheLibFunc) {
   case LibFunc_strlen:
   case LibFunc_wcslen:
     Changed |= setOnlyReadsMemory(F);
     Changed |= setDoesNotThrow(F);
+    Changed |= setOnlyAccessesArgMemory(F);
     Changed |= setDoesNotCapture(F, 0);
     return Changed;
   case LibFunc_strchr:
   case LibFunc_strrchr:
     Changed |= setOnlyReadsMemory(F);
     Changed |= setDoesNotThrow(F);
     return Changed;
   case LibFunc_strtol:

test/Transforms/InferFunctionAttrs/annotate.ll

 declare i8* @strcpy(i8*, i8*)
 
 ; CHECK: declare i64 @strcspn(i8* nocapture, i8* nocapture) [[G1]]
 declare i64 @strcspn(i8*, i8*)
 
 ; CHECK: declare noalias i8* @strdup(i8* nocapture readonly) [[G0]]
 declare i8* @strdup(i8*)
 
-; CHECK: declare i64 @strlen(i8* nocapture) [[G1]]
+; CHECK: declare i64 @strlen(i8* nocapture) [[G2:#[0-9]+]]
 declare i64 @strlen(i8*)
 
 ; CHECK: declare i32 @strncasecmp(i8* nocapture, i8* nocapture, i64) [[G1]]
 declare i32 @strncasecmp(i8*, i8*, i64)
 
 ; CHECK: declare i8* @strncat(i8*, i8* nocapture readonly, i64) [[G0]]
 declare i8* @strncat(i8*, i8*, i64)
 

 ; CHECK: declare i32 @vsscanf(i8* nocapture readonly, i8* nocapture readonly, %opaque*) [[G0]]
 declare i32 @vsscanf(i8*, i8*, %opaque*)
 
 ; CHECK: declare i64 @write(i32, i8* nocapture readonly, i64)
 declare i64 @write(i32, i8*, i64)
 
 
 ; memset_pattern16 isn't available everywhere.
-; CHECK-DARWIN: declare void @memset_pattern16(i8* nocapture, i8* nocapture readonly, i64) [[G2:#[0-9]+]]
+; CHECK-DARWIN: declare void @memset_pattern16(i8* nocapture, i8* nocapture readonly, i64) [[G3:#[0-9]+]]
 declare void @memset_pattern16(i8*, i8*, i64)
 
 
 ; CHECK: attributes [[G0]] = { nounwind }
 ; CHECK: attributes [[G1]] = { nounwind readonly }
-; CHECK-DARWIN: attributes [[G2]] = { argmemonly }
+; CHECK: attributes [[G2]] = { argmemonly nounwind readonly }
+; CHECK-DARWIN: attributes [[G3]] = { argmemonly }

test/Transforms/LICM/strlen.ll

+; RUN: opt < %s -inferattrs -licm | llvm-dis
+
+define void @test(i64* noalias %loc, i8* noalias %a) {
+; CHECK-LABEL: @test
+; CHECK: @strlen
+; CHECK-LABEL: loop:
+  br label %loop
+
+loop:
+  %res = call i64 @strlen(i8* %a)
+  store i64 %res, i64* %loc
+  br label %loop
+}
+
+; CHECK: attributes #0 = { argmemonly nounwind readonly }
+declare i64 @strlen(i8*)
+
+