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std.zig.system: Move CPU feature hacks after ABI detection. #22526

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merged 2 commits into from
Jan 18, 2025
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std.zig.system: Move CPU feature hacks after ABI detection. #22526

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std.zig.system: Move CPU feature hacks after ABI detection.
alexrp Jan 18, 2025
515c970
Revert "work around llvm failing to lower memcpy"
alexrp Jan 18, 2025
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28 changes: 2 additions & 26 deletions lib/compiler_rt/memcpy.zig
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Original file line number Diff line number Diff line change
Expand Up @@ -9,36 +9,12 @@ comptime {
}
}

const llvm_cannot_lower = switch (builtin.cpu.arch) {
.arm, .armeb, .thumb, .thumbeb => builtin.zig_backend == .stage2_llvm,
else => false,
};

fn memcpy(noalias opt_dest: ?[*]u8, noalias opt_src: ?[*]const u8, len: usize) callconv(.C) ?[*]u8 {
if (llvm_cannot_lower) {
for (0..len) |i| opt_dest.?[i] = opt_src.?[i];
return opt_dest;
} else {
return memmove(opt_dest, opt_src, len);
}
return memmove(opt_dest, opt_src, len);
}

/// A port of https://github.com/facebook/folly/blob/1c8bc50e88804e2a7361a57cd9b551dd10f6c5fd/folly/memcpy.S
fn memmove(opt_dest: ?[*]u8, opt_src: ?[*]const u8, len: usize) callconv(.C) ?[*]u8 {
if (llvm_cannot_lower) {
if (@intFromPtr(opt_dest) < @intFromPtr(opt_src)) {
for (0..len) |i| opt_dest.?[i] = opt_src.?[i];
return opt_dest;
} else {
var index = len;
while (index != 0) {
index -= 1;
opt_dest.?[index] = opt_src.?[index];
}
return opt_dest;
}
}

// a port of https://github.com/facebook/folly/blob/1c8bc50e88804e2a7361a57cd9b551dd10f6c5fd/folly/memcpy.S
if (len == 0) {
@branchHint(.unlikely);
return opt_dest;
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32 changes: 18 additions & 14 deletions lib/std/zig/system.zig
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Original file line number Diff line number Diff line change
Expand Up @@ -399,22 +399,26 @@ pub fn resolveTargetQuery(query: Target.Query) DetectError!Target {
query.cpu_features_sub,
);

if (cpu.arch == .hexagon) {
// Both LLVM and LLD have broken support for the small data area. Yet LLVM has the feature
// on by default for all Hexagon CPUs. Clang sort of solves this by defaulting the `-gpsize`
// command line parameter for the Hexagon backend to 0, so that no constants get placed in
// the SDA. (This of course breaks down if the user passes `-G <n>` to Clang...) We can't do
// the `-gpsize` hack because we can have multiple concurrent LLVM emit jobs, and command
// line options in LLVM are shared globally. So just force this feature off. Lovely stuff.
cpu.features.removeFeature(@intFromEnum(Target.hexagon.Feature.small_data));
}
var result = try detectAbiAndDynamicLinker(cpu, os, query);

// https://github.com/llvm/llvm-project/issues/105978
if (cpu.arch.isArm() and query_abi.floatAbi() == .soft) {
cpu.features.removeFeature(@intFromEnum(Target.arm.Feature.vfp2));
}
// These CPU feature hacks have to come after ABI detection.
{
if (result.cpu.arch == .hexagon) {
// Both LLVM and LLD have broken support for the small data area. Yet LLVM has the
// feature on by default for all Hexagon CPUs. Clang sort of solves this by defaulting
// the `-gpsize` command line parameter for the Hexagon backend to 0, so that no
// constants get placed in the SDA. (This of course breaks down if the user passes
// `-G <n>` to Clang...) We can't do the `-gpsize` hack because we can have multiple
// concurrent LLVM emit jobs, and command line options in LLVM are shared globally. So
// just force this feature off. Lovely stuff.
result.cpu.features.removeFeature(@intFromEnum(Target.hexagon.Feature.small_data));
}

var result = try detectAbiAndDynamicLinker(cpu, os, query);
// https://github.com/llvm/llvm-project/issues/105978
if (result.cpu.arch.isArm() and result.abi.floatAbi() == .soft) {
result.cpu.features.removeFeature(@intFromEnum(Target.arm.Feature.vfp2));
}
}

// It's possible that we detect the native ABI, but fail to detect the OS version or were told
// to use the default OS version range. In that case, while we can't determine the exact native
Expand Down