[LibCall] Infer nocallback for libcalls (#135173)

This patch adds `nocallback` attributes for string/math libcalls. It
allows FuncAttributor to infer `norecurse` more precisely and encourages
more aggressive global optimization.

1 files changed, 38 insertions, 1 deletions

diff --git a/llvm/lib/Transforms/Utils/BuildLibCalls.cpp b/llvm/lib/Transforms/Utils/BuildLibCalls.cpp
index 24eefc9..a5f6047 100644
--- a/llvm/lib/Transforms/Utils/BuildLibCalls.cpp
+++ b/llvm/lib/Transforms/Utils/BuildLibCalls.cpp
@@ -47,6 +47,7 @@ STATISTIC(
     NumWriteArgumentMemOrErrnoMemOnly,
     "Number of functions inferred as memory(argmem: write, errnomem: write)");
 STATISTIC(NumNoUnwind, "Number of functions inferred as nounwind");
+STATISTIC(NumNoCallback, "Number of functions inferred as nocallback");
 STATISTIC(NumNoCapture, "Number of arguments inferred as nocapture");
 STATISTIC(NumWriteOnlyArg, "Number of arguments inferred as writeonly");
 STATISTIC(NumReadOnlyArg, "Number of arguments inferred as readonly");
@@ -148,6 +149,14 @@ static bool setDoesNotThrow(Function &F) {
   return true;
 }
 
+static bool setDoesNotCallback(Function &F) {
+  if (F.hasFnAttribute(Attribute::NoCallback))
+    return false;
+  F.addFnAttr(Attribute::NoCallback);
+  ++NumNoCallback;
+  return true;
+}
+
 static bool setRetDoesNotAlias(Function &F) {
   if (F.hasRetAttribute(Attribute::NoAlias))
     return false;
@@ -322,6 +331,7 @@ bool llvm::inferNonMandatoryLibFuncAttrs(Function &F,
   case LibFunc_wcslen:
     Changed |= setOnlyReadsMemory(F);
     Changed |= setDoesNotThrow(F);
+    Changed |= setDoesNotCallback(F);
     Changed |= setOnlyAccessesArgMemory(F);
     Changed |= setWillReturn(F);
     Changed |= setDoesNotCapture(F, 0);
@@ -331,6 +341,7 @@ bool llvm::inferNonMandatoryLibFuncAttrs(Function &F,
     Changed |= setOnlyAccessesArgMemory(F);
     Changed |= setOnlyReadsMemory(F);
     Changed |= setDoesNotThrow(F);
+    Changed |= setDoesNotCallback(F);
     Changed |= setWillReturn(F);
     break;
   case LibFunc_strtol:
@@ -341,6 +352,7 @@ bool llvm::inferNonMandatoryLibFuncAttrs(Function &F,
   case LibFunc_strtold:
   case LibFunc_strtoull:
     Changed |= setDoesNotThrow(F);
+    Changed |= setDoesNotCallback(F);
     Changed |= setWillReturn(F);
     Changed |= setDoesNotCapture(F, 1);
     Changed |= setOnlyReadsMemory(F, 0);
@@ -349,6 +361,7 @@ bool llvm::inferNonMandatoryLibFuncAttrs(Function &F,
   case LibFunc_strncat:
     Changed |= setOnlyAccessesArgMemory(F);
     Changed |= setDoesNotThrow(F);
+    Changed |= setDoesNotCallback(F);
     Changed |= setWillReturn(F);
     Changed |= setReturnedArg(F, 0);
     Changed |= setDoesNotCapture(F, 1);
@@ -364,6 +377,7 @@ bool llvm::inferNonMandatoryLibFuncAttrs(Function &F,
   case LibFunc_stpncpy:
     Changed |= setOnlyAccessesArgMemory(F);
     Changed |= setDoesNotThrow(F);
+    Changed |= setDoesNotCallback(F);
     Changed |= setWillReturn(F);
     Changed |= setDoesNotCapture(F, 1);
     Changed |= setOnlyWritesMemory(F, 0);
@@ -373,6 +387,7 @@ bool llvm::inferNonMandatoryLibFuncAttrs(Function &F,
     break;
   case LibFunc_strxfrm:
     Changed |= setDoesNotThrow(F);
+    Changed |= setDoesNotCallback(F);
     Changed |= setWillReturn(F);
     Changed |= setDoesNotCapture(F, 0);
     Changed |= setDoesNotCapture(F, 1);
@@ -383,6 +398,7 @@ bool llvm::inferNonMandatoryLibFuncAttrs(Function &F,
   case LibFunc_strncmp:     // 0,1
   case LibFunc_strcspn:     // 0,1
     Changed |= setDoesNotThrow(F);
+    Changed |= setDoesNotCallback(F);
     Changed |= setOnlyAccessesArgMemory(F);
     Changed |= setWillReturn(F);
     Changed |= setOnlyReadsMemory(F);
@@ -396,6 +412,7 @@ bool llvm::inferNonMandatoryLibFuncAttrs(Function &F,
     // global memory.
     Changed |= setOnlyReadsMemory(F);
     Changed |= setDoesNotThrow(F);
+    Changed |= setDoesNotCallback(F);
     Changed |= setWillReturn(F);
     Changed |= setDoesNotCapture(F, 0);
     Changed |= setDoesNotCapture(F, 1);
@@ -405,12 +422,14 @@ bool llvm::inferNonMandatoryLibFuncAttrs(Function &F,
     Changed |= setOnlyAccessesArgMemory(F);
     Changed |= setOnlyReadsMemory(F);
     Changed |= setDoesNotThrow(F);
+    Changed |= setDoesNotCallback(F);
     Changed |= setWillReturn(F);
     Changed |= setDoesNotCapture(F, 1);
     break;
   case LibFunc_strtok:
   case LibFunc_strtok_r:
     Changed |= setDoesNotThrow(F);
+    Changed |= setDoesNotCallback(F);
     Changed |= setWillReturn(F);
     Changed |= setDoesNotCapture(F, 1);
     Changed |= setOnlyReadsMemory(F, 1);
@@ -509,6 +528,7 @@ bool llvm::inferNonMandatoryLibFuncAttrs(Function &F,
     Changed |= setOnlyAccessesArgMemory(F);
     Changed |= setOnlyReadsMemory(F);
     Changed |= setDoesNotThrow(F);
+    Changed |= setDoesNotCallback(F);
     Changed |= setWillReturn(F);
     Changed |= setDoesNotCapture(F, 0);
     Changed |= setDoesNotCapture(F, 1);
@@ -516,6 +536,7 @@ bool llvm::inferNonMandatoryLibFuncAttrs(Function &F,
   case LibFunc_memchr:
   case LibFunc_memrchr:
     Changed |= setDoesNotThrow(F);
+    Changed |= setDoesNotCallback(F);
     Changed |= setOnlyAccessesArgMemory(F);
     Changed |= setOnlyReadsMemory(F);
     Changed |= setWillReturn(F);
@@ -524,6 +545,7 @@ bool llvm::inferNonMandatoryLibFuncAttrs(Function &F,
   case LibFunc_modff:
   case LibFunc_modfl:
     Changed |= setDoesNotThrow(F);
+    Changed |= setDoesNotCallback(F);
     Changed |= setWillReturn(F);
     Changed |= setOnlyAccessesArgMemory(F);
     Changed |= setOnlyWritesMemory(F);
@@ -531,6 +553,7 @@ bool llvm::inferNonMandatoryLibFuncAttrs(Function &F,
     break;
   case LibFunc_memcpy:
     Changed |= setDoesNotThrow(F);
+    Changed |= setDoesNotCallback(F);
     Changed |= setOnlyAccessesArgMemory(F);
     Changed |= setWillReturn(F);
     Changed |= setDoesNotAlias(F, 0);
@@ -542,6 +565,7 @@ bool llvm::inferNonMandatoryLibFuncAttrs(Function &F,
     break;
   case LibFunc_memmove:
     Changed |= setDoesNotThrow(F);
+    Changed |= setDoesNotCallback(F);
     Changed |= setOnlyAccessesArgMemory(F);
     Changed |= setWillReturn(F);
     Changed |= setReturnedArg(F, 0);
@@ -555,6 +579,7 @@ bool llvm::inferNonMandatoryLibFuncAttrs(Function &F,
     [[fallthrough]];
   case LibFunc_memcpy_chk:
     Changed |= setDoesNotThrow(F);
+    Changed |= setDoesNotCallback(F);
     Changed |= setOnlyAccessesArgMemory(F);
     Changed |= setDoesNotAlias(F, 0);
     Changed |= setOnlyWritesMemory(F, 0);
@@ -657,6 +682,7 @@ bool llvm::inferNonMandatoryLibFuncAttrs(Function &F,
     break;
   case LibFunc_bcopy:
     Changed |= setDoesNotThrow(F);
+    Changed |= setDoesNotCallback(F);
     Changed |= setOnlyAccessesArgMemory(F);
     Changed |= setWillReturn(F);
     Changed |= setDoesNotCapture(F, 0);
@@ -666,6 +692,7 @@ bool llvm::inferNonMandatoryLibFuncAttrs(Function &F,
     break;
   case LibFunc_bcmp:
     Changed |= setDoesNotThrow(F);
+    Changed |= setDoesNotCallback(F);
     Changed |= setOnlyAccessesArgMemory(F);
     Changed |= setOnlyReadsMemory(F);
     Changed |= setWillReturn(F);
@@ -674,6 +701,7 @@ bool llvm::inferNonMandatoryLibFuncAttrs(Function &F,
     break;
   case LibFunc_bzero:
     Changed |= setDoesNotThrow(F);
+    Changed |= setDoesNotCallback(F);
     Changed |= setOnlyAccessesArgMemory(F);
     Changed |= setWillReturn(F);
     Changed |= setDoesNotCapture(F, 0);
@@ -710,6 +738,7 @@ bool llvm::inferNonMandatoryLibFuncAttrs(Function &F,
   case LibFunc_atof:
   case LibFunc_atoll:
     Changed |= setDoesNotThrow(F);
+    Changed |= setDoesNotCallback(F);
     Changed |= setOnlyReadsMemory(F);
     Changed |= setWillReturn(F);
     Changed |= setDoesNotCapture(F, 0);
@@ -787,6 +816,7 @@ bool llvm::inferNonMandatoryLibFuncAttrs(Function &F,
   case LibFunc_frexpf:
   case LibFunc_frexpl:
     Changed |= setDoesNotThrow(F);
+    Changed |= setDoesNotCallback(F);
     Changed |= setWillReturn(F);
     Changed |= setOnlyAccessesArgMemory(F);
     Changed |= setOnlyWritesMemory(F);
@@ -1025,6 +1055,7 @@ bool llvm::inferNonMandatoryLibFuncAttrs(Function &F,
   case LibFunc_ntohl:
   case LibFunc_ntohs:
     Changed |= setDoesNotThrow(F);
+    Changed |= setDoesNotCallback(F);
     Changed |= setDoesNotAccessMemory(F);
     break;
   case LibFunc_lstat:
@@ -1041,7 +1072,7 @@ bool llvm::inferNonMandatoryLibFuncAttrs(Function &F,
     Changed |= setOnlyReadsMemory(F, 0);
     break;
   case LibFunc_qsort:
-    // May throw; places call through function pointer.
+    // May throw/callback; places call through function pointer.
     // Cannot give undef pointer/size
     Changed |= setRetAndArgsNoUndef(F);
     Changed |= setDoesNotCapture(F, 3);
@@ -1058,6 +1089,7 @@ bool llvm::inferNonMandatoryLibFuncAttrs(Function &F,
     break;
   case LibFunc_dunder_strtok_r:
     Changed |= setDoesNotThrow(F);
+    Changed |= setDoesNotCallback(F);
     Changed |= setDoesNotCapture(F, 1);
     Changed |= setOnlyReadsMemory(F, 1);
     break;
@@ -1149,6 +1181,7 @@ bool llvm::inferNonMandatoryLibFuncAttrs(Function &F,
     Changed |= setOnlyAccessesArgMemory(F);
     Changed |= setOnlyWritesMemory(F, 0);
     Changed |= setDoesNotThrow(F);
+    Changed |= setDoesNotCallback(F);
     break;
   case LibFunc_abort:
     Changed |= setIsCold(F);
@@ -1156,6 +1189,7 @@ bool llvm::inferNonMandatoryLibFuncAttrs(Function &F,
     Changed |= setDoesNotThrow(F);
     break;
   case LibFunc_terminate:
+    // May callback; terminate_handler may be called
     Changed |= setIsCold(F);
     Changed |= setNoReturn(F);
     break;
@@ -1284,6 +1318,7 @@ bool llvm::inferNonMandatoryLibFuncAttrs(Function &F,
   case LibFunc_tanhl:
   case LibFunc_tanl:
     Changed |= setDoesNotThrow(F);
+    Changed |= setDoesNotCallback(F);
     Changed |= setDoesNotFreeMemory(F);
     Changed |= setWillReturn(F);
     Changed |= setOnlyWritesErrnoMemory(F);
@@ -1327,6 +1362,7 @@ bool llvm::inferNonMandatoryLibFuncAttrs(Function &F,
   case LibFunc_isascii:
   case LibFunc_isdigit:
     Changed |= setDoesNotThrow(F);
+    Changed |= setDoesNotCallback(F);
     Changed |= setDoesNotFreeMemory(F);
     Changed |= setWillReturn(F);
     break;
@@ -1340,6 +1376,7 @@ bool llvm::inferNonMandatoryLibFuncAttrs(Function &F,
   case LibFunc_remquof:
   case LibFunc_remquol:
     Changed |= setDoesNotThrow(F);
+    Changed |= setDoesNotCallback(F);
     Changed |= setDoesNotFreeMemory(F);
     Changed |= setOnlyWritesMemory(F, 2);
     Changed |= setDoesNotCapture(F, 2);