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Build ICU with ClangCL so -march actually limits codegen #174

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Merged
dylan-conway merged 2 commits into from
Mar 10, 2026
Merged

Build ICU with ClangCL so -march actually limits codegen #174

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0196080
Build ICU stage 2 with ClangCL so -march limits codegen on x64
dylan-conway Mar 10, 2026
335daa8
Strip .rc from ICU vcxproj since rc.exe cannot parse clang stddef.h
dylan-conway Mar 10, 2026
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10 changes: 9 additions & 1 deletion build-icu.ps1
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Original file line number Diff line number Diff line change
Expand Up @@ -76,11 +76,14 @@ if (-not (Test-Path $ICU_SOURCE_DIR)) {
}

if ($Platform -eq "x64") {
$ArchFlag = if ($Baseline) { "/arch:SSE2" } else { "/arch:AVX2" }
$ArchFlag = if ($Baseline) { "/clang:-march=nehalem" } else { "/clang:-march=haswell" }
} else {
$ArchFlag = ""
}

# ClangCL for stage 2 so -march= limits codegen (MSVC /arch:SSE2 is a no-op on x64).
$ToolsetArg = if ($Platform -eq "x64") { @("/p:PlatformToolset=ClangCL") } else { @() }

# --- Function to patch vcxproj files for static library build with /MT ---
function Patch-IcuVcxProj {
param(
Expand Down Expand Up @@ -125,6 +128,10 @@ function Patch-IcuVcxProj {
$content = $content -replace '<OutputFile>[^<]*\.(dll|DLL)</OutputFile>', ''
$content = $content -replace '<ImportLibrary>[^<]*</ImportLibrary>', ''

# Strip .rc — rc.exe cannot parse clang stddef.h and static libs do not need version resources.
$content = $content -replace "(?s)<ResourceCompile[^>]*>.*?</ResourceCompile>", ""
$content = $content -replace "<ResourceCompile[^>]*/>", ""

# For stubdata - remove resource-only DLL settings
if ($FilePath -match "stubdata") {
$content = $content -replace '<NoEntryPoint>true</NoEntryPoint>', ''
Expand Down Expand Up @@ -235,6 +242,7 @@ foreach ($target in @("common", "i18n")) {
"/v:minimal"
)

$buildArgs += $ToolsetArg
& $msbuildPath $buildArgs

if ($LASTEXITCODE -ne 0) {
Expand Down
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