printf: handle empty string, and string of only null (#1386)

Add tests:
- verify the new case
- verify we don't mess up pointer-to-zero-char4

Fixed: #1385

lib/PrintfPass.cpp

@@ -25,7 +25,7 @@
 
 using namespace llvm;
 
-std::string clspv::PrintfPass::GetStringLiteral(Value *Val) {
+std::optional<std::string> clspv::PrintfPass::GetStringLiteral(Value *Val) {
   GlobalVariable *GlobalVal = nullptr;
   Instruction *ConstExprEquivInstr = nullptr;
   // If opaque pointers aren't enabled, the global may be hidden behind a
@@ -54,9 +54,19 @@ std::string clspv::PrintfPass::GetStringLiteral(Value *Val) {
         return InitArray->getAsString().str();
       }
     }
+    // The empty C string, and strings of null chars, are
+    // constant-aggregate-zero.
+    if (auto *InitArray = dyn_cast<ConstantAggregateZero>(Initializer)) {
+      if (auto *arrTy = dyn_cast<ArrayType>(InitArray->getType())) {
+        if (arrTy->getElementType()->isIntegerTy(8)) {
+          return std::string(arrTy->getNumElements(), '\0');
+        }
+      }
+    }
   }
 
-  return "";
+  // Not a string.
+  return {};
 }
 
 unsigned clspv::PrintfPass::GetPrintfStoreSize(const DataLayout &DL, Type *Ty) {
@@ -278,7 +288,7 @@ PreservedAnalyses clspv::PrintfPass::run(Module &M, ModuleAnalysisManager &) {
     // Check format string is valid
     auto *FmtStringValue = CI->getArgOperand(0);
     auto FmtString = GetStringLiteral(FmtStringValue);
-    if (FmtString == "") {
+    if (!FmtString.has_value()) {
       continue;
     }
 
@@ -292,15 +302,15 @@ PreservedAnalyses clspv::PrintfPass::run(Module &M, ModuleAnalysisManager &) {
 
       // Literal Arg are store using a 32bits identifier, which differs when
       // using 64bits pointers from the size returned by GetPrintfStoreSize.
-      bool IsStringLiteral = GetStringLiteral(Arg) != "";
+      bool IsStringLiteral = GetStringLiteral(Arg).has_value();
       unsigned ArgSize = IsStringLiteral ? 4 : GetPrintfStoreSize(DL, ArgType);
 
       auto *ArgSizeConst = ConstantInt::get(Int32Ty, ArgSize);
       ArgMD.push_back(ConstantAsMetadata::get(ArgSizeConst));
     }
 
     auto *PrintfMD =
-        CreatePrintfArgsMetadata(M, ArgMD, FmtString, PrintfCallID);
+        CreatePrintfArgsMetadata(M, ArgMD, FmtString.value(), PrintfCallID);
     PrintfMDs->addOperand(PrintfMD);
 
     // Get string literal arguments to printf (not including format string) and
@@ -309,10 +319,10 @@ PreservedAnalyses clspv::PrintfPass::run(Module &M, ModuleAnalysisManager &) {
     for (unsigned i = 1; i < CI->arg_size(); i++) {
       Value *Arg = CI->getArgOperand(i);
       auto StringLiteral = GetStringLiteral(Arg);
-      if (StringLiteral != "") {
+      if (StringLiteral.has_value()) {
         auto StringLiteralID = PrintfID++;
-        auto *StringLiteralMD =
-            CreatePrintfArgsMetadata(M, {}, StringLiteral, StringLiteralID);
+        auto *StringLiteralMD = CreatePrintfArgsMetadata(
+            M, {}, StringLiteral.value(), StringLiteralID);
         PrintfMDs->addOperand(StringLiteralMD);
 
         // The printf now stores the string's ID rather than its data

lib/PrintfPass.h

@@ -14,6 +14,7 @@
 
 #include "llvm/IR/Module.h"
 #include "llvm/IR/PassManager.h"
+#include <optional>
 
 #ifndef _CLSPV_LIB_PRINTF_PASS_H
 #define _CLSPV_LIB_PRINTF_PASS_H
@@ -24,8 +25,8 @@ struct PrintfPass : llvm::PassInfoMixin<PrintfPass> {
 
 private:
   // Find the underlying compile-time string literal, if any, for the given
-  // value
-  std::string GetStringLiteral(llvm::Value *);
+  // value.
+  std::optional<std::string> GetStringLiteral(llvm::Value *);
 
   // Get the printf buffer storage size for the given type
   unsigned GetPrintfStoreSize(const llvm::DataLayout &DL, llvm::Type *Ty);

test/Printf/printf_ptr_to_char4_zero.ll

@@ -0,0 +1,49 @@
+; RUN: clspv-opt %s -o %t.ll --passes=printf-pass
+; RUN: FileCheck %s < %t.ll
+
+; Test this program:
+;   __constant char4 vc = (char4)(0,0,0,0);
+;   kernel void m() { printf("%v4hhd", &vc);
+;
+; This the initializer for vc is a constant-aggregate-zero, but of vector type, not array type.
+; This justifies the check for array type when trying to see if the argument is a string.
+
+; CHECK: !clspv.printf_metadata = !{![[FMT:[0-9]+]]}
+; CHECK: ![[FMT]] = !{i32 0, !"%v4hhd\00",
+
+target datalayout = "e-p:32:32-i64:64-v16:16-v24:32-v32:32-v48:64-v96:128-v192:256-v256:256-v512:512-v1024:1024-G1"
+target triple = "spir-unknown-unknown"
+
+@vc = addrspace(2) constant <4 x i8> zeroinitializer, align 4
+@.str = private unnamed_addr addrspace(2) constant [7 x i8] c"%v4hhd\00", align 1
+@__spirv_WorkgroupSize = addrspace(8) global <3 x i32> zeroinitializer
+
+; Function Attrs: convergent norecurse nounwind
+define dso_local spir_kernel void @m() #0 !kernel_arg_addr_space !6 !kernel_arg_access_qual !6 !kernel_arg_type !6 !kernel_arg_base_type !6 !kernel_arg_type_qual !6 !kernel_arg_name !6 !clspv.pod_args_impl !7 {
+entry:
+  %call = call spir_func i32 (ptr addrspace(2), ...) @printf(ptr addrspace(2) @.str, ptr addrspace(2) @vc) #2
+  ret void
+}
+
+; Function Attrs: convergent nounwind
+declare !kernel_arg_name !8 spir_func i32 @printf(ptr addrspace(2), ...) #1
+
+attributes #0 = { convergent norecurse nounwind "no-builtins" "no-trapping-math"="true" "stack-protector-buffer-size"="0" "stackrealign" "uniform-work-group-size"="true" }
+attributes #1 = { convergent nounwind "no-builtins" "no-trapping-math"="true" "stack-protector-buffer-size"="0" "stackrealign" }
+attributes #2 = { convergent nobuiltin nounwind "no-builtins" }
+
+!llvm.module.flags = !{!0, !1, !2}
+!opencl.ocl.version = !{!3}
+!opencl.spir.version = !{!3, !3, !3, !3, !3, !3, !3, !3, !3, !3, !3, !3, !3, !3, !3, !3, !3, !3, !3, !3, !3, !3, !3, !3, !3, !3, !3, !3, !3, !3, !3, !3, !3, !3, !3, !3, !3, !3, !3, !3, !3, !3, !3, !3, !3, !3, !3, !3, !3, !3, !3, !3, !3, !3, !3, !3, !3, !3, !3, !3, !3, !3, !3, !3, !3, !3, !3, !3, !3, !3, !3, !3, !3, !3, !3, !3, !3, !3, !3, !3, !3, !3, !3, !3, !3, !3, !3, !3, !3, !3}
+!llvm.ident = !{!4, !4, !4, !4, !4, !4, !4, !4, !4, !4, !4, !4, !4, !4, !4, !4, !4, !4, !4, !4, !4, !4, !4, !4, !4, !4, !4, !4, !4, !4, !4, !4, !4, !4, !4, !4, !4, !4, !4, !4, !4, !4, !4, !4, !4, !4, !4, !4, !4, !4, !4, !4, !4, !4, !4, !4, !4, !4, !4, !4, !4, !4, !4, !4, !4, !4, !4, !4, !4, !4, !4, !4, !4, !4, !4, !4, !4, !4, !4, !4, !4, !4, !4, !4, !4, !4, !4, !4, !4, !4}
+!_Z28clspv.entry_point_attributes = !{!5}
+
+!0 = !{i32 1, !"wchar_size", i32 4}
+!1 = !{i32 7, !"direct-access-external-data", i32 0}
+!2 = !{i32 7, !"frame-pointer", i32 2}
+!3 = !{i32 1, i32 2}
+!4 = !{!"clang version 19.0.0git (https://github.com/llvm/llvm-project 402eca265f7162e26b8b74d18297fd76c9f100de)"}
+!5 = !{!"m", !"kernel"}
+!6 = !{}
+!7 = !{i32 2}
+!8 = !{!""}

test/Printf/printf_string_only_null.ll

@@ -0,0 +1,46 @@
+; RUN: clspv-opt %s -o %t.ll --passes=printf-pass
+; RUN: FileCheck %s < %t.ll
+
+; Test printf("", "\0\0\0");
+; The value is a ConstantAggregateZero whose type is array of i8
+
+; CHECK: !clspv.printf_metadata = !{![[FMT:[0-9]+]], ![[LITERAL:[0-9]+]]}
+; CHECK: ![[FMT]] = !{i32 0, !"\00",
+; CHECK: ![[LITERAL]] = !{i32 1, !"\00\00\00\00",
+
+target datalayout = "e-p:32:32-i64:64-v16:16-v24:32-v32:32-v48:64-v96:128-v192:256-v256:256-v512:512-v1024:1024-G1"
+target triple = "spir-unknown-unknown"
+
+@.str = private unnamed_addr addrspace(2) constant [1 x i8] zeroinitializer, align 1
+@.str.1 = private unnamed_addr addrspace(2) constant [4 x i8] zeroinitializer, align 1
+@__spirv_WorkgroupSize = addrspace(8) global <3 x i32> zeroinitializer
+
+; Function Attrs: convergent norecurse nounwind
+define dso_local spir_kernel void @m() #0 !kernel_arg_addr_space !6 !kernel_arg_access_qual !6 !kernel_arg_type !6 !kernel_arg_base_type !6 !kernel_arg_type_qual !6 !kernel_arg_name !6 !clspv.pod_args_impl !7 {
+entry:
+  %call = call spir_func i32 (ptr addrspace(2), ...) @printf(ptr addrspace(2) @.str, ptr addrspace(2) @.str.1) #2
+  ret void
+}
+
+; Function Attrs: convergent nounwind
+declare !kernel_arg_name !8 spir_func i32 @printf(ptr addrspace(2), ...) #1
+
+attributes #0 = { convergent norecurse nounwind "no-builtins" "no-trapping-math"="true" "stack-protector-buffer-size"="0" "stackrealign" "uniform-work-group-size"="true" }
+attributes #1 = { convergent nounwind "no-builtins" "no-trapping-math"="true" "stack-protector-buffer-size"="0" "stackrealign" }
+attributes #2 = { convergent nobuiltin nounwind "no-builtins" }
+
+!llvm.module.flags = !{!0, !1, !2}
+!opencl.ocl.version = !{!3}
+!opencl.spir.version = !{!3, !3, !3, !3, !3, !3, !3, !3, !3, !3, !3, !3, !3, !3, !3, !3, !3, !3, !3, !3, !3, !3, !3, !3, !3, !3, !3, !3, !3, !3, !3, !3, !3, !3, !3, !3, !3, !3, !3, !3, !3, !3, !3, !3, !3, !3, !3, !3, !3, !3, !3, !3, !3, !3, !3, !3, !3, !3, !3, !3, !3, !3, !3, !3, !3, !3, !3, !3, !3, !3, !3, !3, !3, !3, !3, !3, !3, !3, !3, !3, !3, !3, !3, !3, !3, !3, !3, !3, !3, !3}
+!llvm.ident = !{!4, !4, !4, !4, !4, !4, !4, !4, !4, !4, !4, !4, !4, !4, !4, !4, !4, !4, !4, !4, !4, !4, !4, !4, !4, !4, !4, !4, !4, !4, !4, !4, !4, !4, !4, !4, !4, !4, !4, !4, !4, !4, !4, !4, !4, !4, !4, !4, !4, !4, !4, !4, !4, !4, !4, !4, !4, !4, !4, !4, !4, !4, !4, !4, !4, !4, !4, !4, !4, !4, !4, !4, !4, !4, !4, !4, !4, !4, !4, !4, !4, !4, !4, !4, !4, !4, !4, !4, !4, !4}
+!_Z28clspv.entry_point_attributes = !{!5}
+
+!0 = !{i32 1, !"wchar_size", i32 4}
+!1 = !{i32 7, !"direct-access-external-data", i32 0}
+!2 = !{i32 7, !"frame-pointer", i32 2}
+!3 = !{i32 1, i32 2}
+!4 = !{!"clang version 19.0.0git (https://github.com/llvm/llvm-project 402eca265f7162e26b8b74d18297fd76c9f100de)"}
+!5 = !{!"m", !"kernel"}
+!6 = !{}
+!7 = !{i32 2}
+!8 = !{!""}