Replace '0' with 'z' for all-zero value

Author: shiltian

llvm/docs/LangRef.rst

@@ -3145,7 +3145,7 @@ as follows:
     denotes the default address space 0. The value of ``n`` must be
     in the range [1,2^24). The fifth parameter ``<sentinel>`` specifies the
     sentinel value of the pointer for the corresponding address space. It
-    currently accepts two values: ``0`` for an all-zero value and ``f`` for a
+    currently accepts two values: ``z`` for an all-zero value and ``f`` for a
     full-bit set value. The default sentinel pointer value is all-zero.
 ``i<size>:<abi>[:<pref>]``
     This specifies the alignment for an integer type of a given bit

llvm/lib/IR/DataLayout.cpp

@@ -302,16 +302,16 @@ static Error parseSentinelValue(StringRef Str, APInt &V) {
   if (Str.empty())
     return createStringError("sentinel value component cannot be empty");
   if (Str.size() != 1)
-    return createStringError("sentinel value component must be a '0' or 'f'");
-  if (Str[0] == '0') {
+    return createStringError("sentinel value component must be a 'z' or 'f'");
+  if (Str[0] == 'z') {
     V.clearAllBits();
     return Error::success();
   }
   if (Str[0] == 'f') {
     V.setAllBits();
     return Error::success();
   }
-  return createStringError("sentinel value component must be a '0' or 'f'");
+  return createStringError("sentinel value component must be a 'z' or 'f'");
 }
 
 /// Attempts to parse an alignment component of a specification.

llvm/unittests/IR/DataLayoutTest.cpp

@@ -408,7 +408,7 @@ TEST(DataLayout, ParsePointerSpec) {
        {"p:32:32:32:32:a", "p0:32:32:32:32:ab", "p42:32:32:32:32:123"})
     EXPECT_THAT_EXPECTED(
         DataLayout::parse(Str),
-        FailedWithMessage("sentinel value component must be a '0' or 'f'"));
+        FailedWithMessage("sentinel value component must be a 'z' or 'f'"));
 
   for (StringRef Str :
        {"p:32:32:32:32:", "p0:32:32:32:32:", "p42:32:32:32:32:"})