TargetLibraryInfo: Stop guessing wchar_t size

Usually the frontend communicates the size of wchar_t via metadata and
we can optimize wcslen (and possibly other calls in the future). In
cases without the wchar_size metadata we would previously try to guess
the correct size based on the target triple; however this is fragile to
keep up to date and may miss users manually changing the size via flags.
Better be safe and stop guessing and optimizing if the frontend didn't
communicate the size.

Differential Revision: https://reviews.llvm.org/D38106

llvm-svn: 314185

llvm/include/llvm/Analysis/TargetLibraryInfo.h

@@ -193,13 +193,9 @@ class TargetLibraryInfoImpl {
     ShouldSignExtI32Param = Val;
   }
 
-  /// Returns the size of the wchar_t type in bytes.
+  /// Returns the size of the wchar_t type in bytes or 0 if the size is unknown.
+  /// This queries the 'wchar_size' metadata.
   unsigned getWCharSize(const Module &M) const;
-
-  /// Returns size of the default wchar_t type on target \p T. This is mostly
-  /// intended to verify that the size in the frontend matches LLVM. All other
-  /// queries should use getWCharSize() instead.
-  static unsigned getTargetWCharSize(const Triple &T);
 };
 
 /// Provides information about what library functions are available for

llvm/lib/Analysis/TargetLibraryInfo.cpp

@@ -1519,20 +1519,11 @@ TargetLibraryInfoImpl &TargetLibraryAnalysis::lookupInfoImpl(const Triple &T) {
   return *Impl;
 }
 
-unsigned TargetLibraryInfoImpl::getTargetWCharSize(const Triple &T) {
-  // See also clang/lib/Basic/Targets.cpp.
-  if (T.isPS4() || T.isOSWindows() || T.isArch16Bit())
-    return 2;
-  if (T.getArch() == Triple::xcore)
-    return 1;
-  return 4;
-}
-
 unsigned TargetLibraryInfoImpl::getWCharSize(const Module &M) const {
   if (auto *ShortWChar = cast_or_null<ConstantAsMetadata>(
       M.getModuleFlag("wchar_size")))
     return cast<ConstantInt>(ShortWChar->getValue())->getZExtValue();
-  return getTargetWCharSize(Triple(M.getTargetTriple()));
+  return 0;
 }
 
 TargetLibraryInfoWrapperPass::TargetLibraryInfoWrapperPass()

llvm/lib/Transforms/Utils/SimplifyLibCalls.cpp

@@ -508,6 +508,9 @@ Value *LibCallSimplifier::optimizeStrLen(CallInst *CI, IRBuilder<> &B) {
 Value *LibCallSimplifier::optimizeWcslen(CallInst *CI, IRBuilder<> &B) {
   Module &M = *CI->getParent()->getParent()->getParent();
   unsigned WCharSize = TLI->getWCharSize(M) * 8;
+  // We cannot perform this optimization without wchar_size metadata.
+  if (WCharSize == 0)
+    return nullptr;
 
   return optimizeStringLength(CI, B, WCharSize);
 }

llvm/test/Transforms/InstCombine/wcslen-1.ll

@@ -7,6 +7,9 @@ target datalayout = "e-m:o-i64:64-f80:128-n8:16:32:64-S128"
 
 declare i64 @wcslen(i32*)
 
+!0 = !{i32 1, !"wchar_size", i32 4}
+!llvm.module.flags = !{!0}
+
 @hello = constant [6 x i32] [i32 104, i32 101, i32 108, i32 108, i32 111, i32 0]
 @longer = constant [7 x i32] [i32 108, i32 111, i32 110, i32 103, i32 101, i32 114, i32 0]
 @null = constant [1 x i32] zeroinitializer

llvm/test/Transforms/InstCombine/wcslen-2.ll

@@ -4,6 +4,9 @@
 
 target datalayout = "e-m:o-i64:64-f80:128-n8:16:32:64-S128"
 
+!0 = !{i32 1, !"wchar_size", i32 4}
+!llvm.module.flags = !{!0}
+
 @hello = constant [6 x i32] [i32 104, i32 101, i32 108, i32 108, i32 111, i32 0]
 
 declare i64 @wcslen(i32*, i32)

llvm/test/Transforms/InstCombine/wcslen-4.ll

@@ -0,0 +1,20 @@
+; Test that the wcslen library call simplifier works correctly.
+;
+; RUN: opt < %s -instcombine -S | FileCheck %s
+
+target datalayout = "e-m:o-i64:64-f80:128-n8:16:32:64-S128"
+
+; Without the wchar_size metadata we should see no optimization happening.
+
+@hello = constant [6 x i32] [i32 104, i32 101, i32 108, i32 108, i32 111, i32 0]
+
+declare i64 @wcslen(i32*)
+
+define i64 @test_no_simplify1() {
+; CHECK-LABEL: @test_no_simplify1(
+; CHECK-NEXT: %hello_l = call i64 @wcslen(i32* getelementptr inbounds ([6 x i32], [6 x i32]* @hello, i64 0, i64 0))
+; CHECK-NEXT: ret i64 %hello_l
+  %hello_p = getelementptr [6 x i32], [6 x i32]* @hello, i64 0, i64 0
+  %hello_l = call i64 @wcslen(i32* %hello_p)
+  ret i64 %hello_l
+}