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compiler: mark string parameters as readonly #5068

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Merged
merged 1 commit into from
Oct 11, 2025
Merged

compiler: mark string parameters as readonly #5068

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8 changes: 8 additions & 0 deletions compiler/calls.go
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Original file line number Diff line number Diff line change
Expand Up @@ -32,6 +32,9 @@ const (
// Whether this is a full or partial Go parameter (int, slice, etc).
// The extra context parameter is not a Go parameter.
paramIsGoParam = 1 << iota

// Whether this is a readonly parameter (for example, a string pointer).
paramIsReadonly
)

// createRuntimeCallCommon creates a runtime call. Use createRuntimeCall or
Expand Down Expand Up @@ -167,6 +170,7 @@ func (c *compilerContext) flattenAggregateType(t llvm.Type, name string, goType
continue
}
suffix := strconv.Itoa(i)
isString := false
if goType != nil {
// Try to come up with a good suffix for this struct field,
// depending on which Go type it's based on.
Expand All @@ -183,12 +187,16 @@ func (c *compilerContext) flattenAggregateType(t llvm.Type, name string, goType
suffix = []string{"r", "i"}[i]
case types.String:
suffix = []string{"data", "len"}[i]
isString = true
}
case *types.Signature:
suffix = []string{"context", "funcptr"}[i]
}
}
subInfos := c.flattenAggregateType(subfield, name+"."+suffix, extractSubfield(goType, i))
if isString {
subInfos[0].flags |= paramIsReadonly
}
paramInfos = append(paramInfos, subInfos...)
}
return paramInfos
Expand Down
5 changes: 5 additions & 0 deletions compiler/symbol.go
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Expand Up @@ -142,6 +142,11 @@ func (c *compilerContext) getFunction(fn *ssa.Function) (llvm.Type, llvm.Value)
nocapture := c.ctx.CreateEnumAttribute(llvm.AttributeKindID("nocapture"), 0)
llvmFn.AddAttributeAtIndex(i+1, nocapture)
}
if paramInfo.flags&paramIsReadonly != 0 && paramInfo.llvmType.TypeKind() == llvm.PointerTypeKind {
// Readonly pointer parameters (like strings) benefit from being marked as readonly.
readonly := c.ctx.CreateEnumAttribute(llvm.AttributeKindID("readonly"), 0)
llvmFn.AddAttributeAtIndex(i+1, readonly)
}
}

// Set a number of function or parameter attributes, depending on the
Expand Down
2 changes: 1 addition & 1 deletion compiler/testdata/go1.20.ll
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Expand Up @@ -50,7 +50,7 @@ unsafe.String.throw: ; preds = %entry
declare void @runtime.unsafeSlicePanic(ptr) #1

; Function Attrs: nounwind
define hidden ptr @main.unsafeStringData(ptr %s.data, i32 %s.len, ptr %context) unnamed_addr #2 {
define hidden ptr @main.unsafeStringData(ptr readonly %s.data, i32 %s.len, ptr %context) unnamed_addr #2 {
entry:
%stackalloc = alloca i8, align 1
call void @runtime.trackPointer(ptr %s.data, ptr nonnull %stackalloc, ptr undef) #3
Expand Down
6 changes: 3 additions & 3 deletions compiler/testdata/go1.21.ll
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Expand Up @@ -77,7 +77,7 @@ entry:
}

; Function Attrs: nounwind
define hidden %runtime._string @main.minString(ptr %a.data, i32 %a.len, ptr %b.data, i32 %b.len, ptr %context) unnamed_addr #2 {
define hidden %runtime._string @main.minString(ptr readonly %a.data, i32 %a.len, ptr readonly %b.data, i32 %b.len, ptr %context) unnamed_addr #2 {
entry:
%0 = insertvalue %runtime._string zeroinitializer, ptr %a.data, 0
%1 = insertvalue %runtime._string %0, i32 %a.len, 1
Expand All @@ -91,7 +91,7 @@ entry:
ret %runtime._string %5
}

declare i1 @runtime.stringLess(ptr, i32, ptr, i32, ptr) #1
declare i1 @runtime.stringLess(ptr readonly, i32, ptr readonly, i32, ptr) #1

; Function Attrs: nounwind
define hidden i32 @main.maxInt(i32 %a, i32 %b, ptr %context) unnamed_addr #2 {
Expand All @@ -116,7 +116,7 @@ entry:
}

; Function Attrs: nounwind
define hidden %runtime._string @main.maxString(ptr %a.data, i32 %a.len, ptr %b.data, i32 %b.len, ptr %context) unnamed_addr #2 {
define hidden %runtime._string @main.maxString(ptr readonly %a.data, i32 %a.len, ptr readonly %b.data, i32 %b.len, ptr %context) unnamed_addr #2 {
entry:
%0 = insertvalue %runtime._string zeroinitializer, ptr %a.data, 0
%1 = insertvalue %runtime._string %0, i32 %a.len, 1
Expand Down
16 changes: 8 additions & 8 deletions compiler/testdata/string.ll
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Expand Up @@ -31,13 +31,13 @@ entry:
}

; Function Attrs: nounwind
define hidden i32 @main.stringLen(ptr %s.data, i32 %s.len, ptr %context) unnamed_addr #2 {
define hidden i32 @main.stringLen(ptr readonly %s.data, i32 %s.len, ptr %context) unnamed_addr #2 {
entry:
ret i32 %s.len
}

; Function Attrs: nounwind
define hidden i8 @main.stringIndex(ptr %s.data, i32 %s.len, i32 %index, ptr %context) unnamed_addr #2 {
define hidden i8 @main.stringIndex(ptr readonly %s.data, i32 %s.len, i32 %index, ptr %context) unnamed_addr #2 {
entry:
%.not = icmp ult i32 %index, %s.len
br i1 %.not, label %lookup.next, label %lookup.throw
Expand All @@ -55,33 +55,33 @@ lookup.throw: ; preds = %entry
declare void @runtime.lookupPanic(ptr) #1

; Function Attrs: nounwind
define hidden i1 @main.stringCompareEqual(ptr %s1.data, i32 %s1.len, ptr %s2.data, i32 %s2.len, ptr %context) unnamed_addr #2 {
define hidden i1 @main.stringCompareEqual(ptr readonly %s1.data, i32 %s1.len, ptr readonly %s2.data, i32 %s2.len, ptr %context) unnamed_addr #2 {
entry:
%0 = call i1 @runtime.stringEqual(ptr %s1.data, i32 %s1.len, ptr %s2.data, i32 %s2.len, ptr undef) #3
ret i1 %0
}

declare i1 @runtime.stringEqual(ptr, i32, ptr, i32, ptr) #1
declare i1 @runtime.stringEqual(ptr readonly, i32, ptr readonly, i32, ptr) #1

; Function Attrs: nounwind
define hidden i1 @main.stringCompareUnequal(ptr %s1.data, i32 %s1.len, ptr %s2.data, i32 %s2.len, ptr %context) unnamed_addr #2 {
define hidden i1 @main.stringCompareUnequal(ptr readonly %s1.data, i32 %s1.len, ptr readonly %s2.data, i32 %s2.len, ptr %context) unnamed_addr #2 {
entry:
%0 = call i1 @runtime.stringEqual(ptr %s1.data, i32 %s1.len, ptr %s2.data, i32 %s2.len, ptr undef) #3
%1 = xor i1 %0, true
ret i1 %1
}

; Function Attrs: nounwind
define hidden i1 @main.stringCompareLarger(ptr %s1.data, i32 %s1.len, ptr %s2.data, i32 %s2.len, ptr %context) unnamed_addr #2 {
define hidden i1 @main.stringCompareLarger(ptr readonly %s1.data, i32 %s1.len, ptr readonly %s2.data, i32 %s2.len, ptr %context) unnamed_addr #2 {
entry:
%0 = call i1 @runtime.stringLess(ptr %s2.data, i32 %s2.len, ptr %s1.data, i32 %s1.len, ptr undef) #3
ret i1 %0
}

declare i1 @runtime.stringLess(ptr, i32, ptr, i32, ptr) #1
declare i1 @runtime.stringLess(ptr readonly, i32, ptr readonly, i32, ptr) #1

; Function Attrs: nounwind
define hidden i8 @main.stringLookup(ptr %s.data, i32 %s.len, i8 %x, ptr %context) unnamed_addr #2 {
define hidden i8 @main.stringLookup(ptr readonly %s.data, i32 %s.len, i8 %x, ptr %context) unnamed_addr #2 {
entry:
%0 = zext i8 %x to i32
%.not = icmp ugt i32 %s.len, %0
Expand Down