[SYCL-MLIR] Use SmallString<0> to store arguments in ArgumentList (#7274)

std::string performs short string optimizations, so that moving an
std::string might invalidate iterators to it. On the other hand,
llvm::SmallString<0> is always heap-allocated, so moving does not
involve invalidation.

Signed-off-by: Victor Perez <[email protected]>

Signed-off-by: Victor Perez <[email protected]>

Author: victor-eds

polygeist/tools/cgeist/Options.h

@@ -13,6 +13,7 @@
 #ifndef CGEIST_OPTIONS_H_
 #define CGEIST_OPTIONS_H_
 
+#include "llvm/ADT/SmallString.h"
 #include "llvm/Passes/OptimizationLevel.h"
 #include "llvm/Support/CommandLine.h"
 #include <string>
@@ -29,12 +30,11 @@ class ArgumentList {
   ///
   /// The element stored will be owned by this.
   template <typename... ArgTy> void emplace_back(ArgTy &&...Args) {
-    // Store as a string
-    std::string Buffer;
-    llvm::raw_string_ostream Stream(Buffer);
-    (Stream << ... << Args);
-    Storage.push_back(Stream.str());
-    push_back(Storage.back());
+    // Store as a SmallString
+    push_back(Storage
+                  .emplace_back(std::initializer_list<llvm::StringRef>{
+                      std::forward<ArgTy>(Args)...})
+                  .c_str());
   }
 
   /// Return the underling argument list.
@@ -45,7 +45,9 @@ class ArgumentList {
 
 private:
   /// Helper storage.
-  llvm::SmallVector<std::string> Storage;
+  ///
+  /// llvm::SmallString<0> is needed to enforce heap allocation.
+  llvm::SmallVector<llvm::SmallString<0>> Storage;
   /// List of arguments
   llvm::SmallVector<const char *> Args;
 };

polygeist/tools/cgeist/Test/Verification/defines.c

@@ -0,0 +1,14 @@
+// RUN: cgeist -DPASS -DTEST0 -DTEST1 -DTEST2 %s -S -o -
+
+// CHECK-LABEL: func.func @main() -> i32 attributes {llvm.linkage = #llvm.linkage<external>} {
+// CHECK-NEXT:    %c0_i32 = arith.constant 0 : i32
+// CHECK-NEXT:    return %c0_i32 : i32
+// CHECK-NEXT:  }
+
+int main() {
+#ifdef PASS
+  return 0;
+#else
+  return 1;
+#endif
+}