121 lines
4.5 KiB
Diff
121 lines
4.5 KiB
Diff
From bf51015656ff3b1bbe6b41ea1155610178c2961d Mon Sep 17 00:00:00 2001
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From: Ayke van Laethem <aykevanlaethem@gmail.com>
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Date: Thu, 21 Sep 2023 15:39:06 +0200
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Subject: [PATCH 4/7] transform: fix bug in StringToBytes optimization pass
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Previously, this pass would convert any read-only use of a
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runtime.stringToBytes call to use the original string buffer instead.
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This is incorrect: if there are any writes to the resulting buffer, none
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of the slice buffer pointers can be converted to use the original
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read-only string buffer.
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This commit fixes that bug and adds a test to prove the new (correct)
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behavior.
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Signed-off-by: Elliott Sales de Andrade <quantum.analyst@gmail.com>
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---
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transform/rtcalls.go | 24 ++++++++++++++++++------
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transform/testdata/stringtobytes.ll | 16 ++++++++++++++++
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transform/testdata/stringtobytes.out.ll | 10 ++++++++++
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3 files changed, 44 insertions(+), 6 deletions(-)
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diff --git a/transform/rtcalls.go b/transform/rtcalls.go
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index 36d2853b..0b6feff2 100644
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--- a/transform/rtcalls.go
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+++ b/transform/rtcalls.go
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@@ -28,32 +28,44 @@ func OptimizeStringToBytes(mod llvm.Module) {
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// strptr is always constant because strings are always constant.
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- convertedAllUses := true
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+ var pointerUses []llvm.Value
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+ canConvertPointer := true
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for _, use := range getUses(call) {
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if use.IsAExtractValueInst().IsNil() {
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// Expected an extractvalue, but this is something else.
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- convertedAllUses = false
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+ canConvertPointer = false
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continue
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}
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switch use.Type().TypeKind() {
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case llvm.IntegerTypeKind:
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// A length (len or cap). Propagate the length value.
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+ // This can always be done because the byte slice is always the
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+ // same length as the original string.
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use.ReplaceAllUsesWith(strlen)
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use.EraseFromParentAsInstruction()
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case llvm.PointerTypeKind:
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// The string pointer itself.
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if !isReadOnly(use) {
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- convertedAllUses = false
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+ // There is a store to the byte slice. This means that none
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+ // of the pointer uses can't be propagated.
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+ canConvertPointer = false
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continue
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}
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- use.ReplaceAllUsesWith(strptr)
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- use.EraseFromParentAsInstruction()
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+ // It may be that the pointer value can be propagated, if all of
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+ // the pointer uses are readonly.
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+ pointerUses = append(pointerUses, use)
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default:
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// should not happen
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panic("unknown return type of runtime.stringToBytes: " + use.Type().String())
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}
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}
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- if convertedAllUses {
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+ if canConvertPointer {
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+ // All pointer uses are readonly, so they can be converted.
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+ for _, use := range pointerUses {
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+ use.ReplaceAllUsesWith(strptr)
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+ use.EraseFromParentAsInstruction()
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+ }
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+
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// Call to runtime.stringToBytes can be eliminated: both the input
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// and the output is constant.
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call.EraseFromParentAsInstruction()
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diff --git a/transform/testdata/stringtobytes.ll b/transform/testdata/stringtobytes.ll
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index fa43f3d0..06373a51 100644
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--- a/transform/testdata/stringtobytes.ll
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+++ b/transform/testdata/stringtobytes.ll
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@@ -30,3 +30,19 @@ entry:
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call fastcc void @writeToSlice(ptr %1, i64 %2, i64 %3)
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ret void
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}
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+
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+; Test that pointer values are never propagated if there is even a single write
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+; to the pointer value (but len/cap values still can be).
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+define void @testReadSome() {
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+entry:
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+ %s = call fastcc { ptr, i64, i64 } @runtime.stringToBytes(ptr @str, i64 6)
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+ %s.ptr = extractvalue { ptr, i64, i64 } %s, 0
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+ %s.len = extractvalue { ptr, i64, i64 } %s, 1
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+ %s.cap = extractvalue { ptr, i64, i64 } %s, 2
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+ call fastcc void @writeToSlice(ptr %s.ptr, i64 %s.len, i64 %s.cap)
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+ %s.ptr2 = extractvalue { ptr, i64, i64 } %s, 0
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+ %s.len2 = extractvalue { ptr, i64, i64 } %s, 1
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+ %s.cap2 = extractvalue { ptr, i64, i64 } %s, 2
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+ call fastcc void @printSlice(ptr %s.ptr2, i64 %s.len2, i64 %s.cap2)
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+ ret void
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+}
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diff --git a/transform/testdata/stringtobytes.out.ll b/transform/testdata/stringtobytes.out.ll
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index 30aa520a..b33a1755 100644
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--- a/transform/testdata/stringtobytes.out.ll
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+++ b/transform/testdata/stringtobytes.out.ll
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@@ -22,3 +22,13 @@ entry:
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call fastcc void @writeToSlice(ptr %1, i64 6, i64 6)
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ret void
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}
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+
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+define void @testReadSome() {
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+entry:
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+ %s = call fastcc { ptr, i64, i64 } @runtime.stringToBytes(ptr @str, i64 6)
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+ %s.ptr = extractvalue { ptr, i64, i64 } %s, 0
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+ call fastcc void @writeToSlice(ptr %s.ptr, i64 6, i64 6)
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+ %s.ptr2 = extractvalue { ptr, i64, i64 } %s, 0
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+ call fastcc void @printSlice(ptr %s.ptr2, i64 6, i64 6)
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+ ret void
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+}
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--
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2.41.0
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