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codegen/llvm: add workarounds to loadTruncate() for llvm codegen bugs

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for wasm, as a heuritic, only enable truncation for values smaller than 32bits.
 -> the bug is no longer triggered in most use cases (or at least the test suite...)

as for powerpc, adding a redundant `and mask` produces working code.
This commit is contained in:
Xavier Bouchoux 2023-10-08 11:35:33 +02:00
parent 370662c565
commit 40528b8a93
1 changed files with 22 additions and 2 deletions
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24
src/codegen/llvm.zig
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@ -10333,8 +10333,20 @@ pub const FuncGen = struct {
const o = fg.dg.object;
const mod = o.module;
const payload_llvm_ty = try o.lowerType(payload_ty);
const abi_size = payload_ty.abiSize(mod);
// llvm bug workarounds:
const workaround_explicit_mask = o.target.cpu.arch == .powerpc and abi_size >= 4;
const workaround_disable_truncate = o.target.cpu.arch == .wasm32 and abi_size >= 4;
if (workaround_disable_truncate) {
// see https://github.com/llvm/llvm-project/issues/64222
// disable the truncation codepath for larger that 32bits value - with this heuristic, the backend passes the test suite.
return try fg.wip.load(access_kind, payload_llvm_ty, payload_ptr, payload_alignment, "");
}
const load_llvm_ty = if (payload_ty.isAbiInt(mod))
try o.builder.intType(@intCast(payload_ty.abiSize(mod) * 8))
try o.builder.intType(@intCast(abi_size * 8))
else
payload_llvm_ty;
const loaded = try fg.wip.load(access_kind, load_llvm_ty, payload_ptr, payload_alignment, "");
@ -10345,7 +10357,15 @@ pub const FuncGen = struct {
), "")
else
loaded;
return fg.wip.conv(.unneeded, shifted, payload_llvm_ty, "");
const anded = if (workaround_explicit_mask and payload_llvm_ty != load_llvm_ty) blk: {
// this is rendundant with llvm.trunc. But without it, llvm17 emits invalid code for powerpc.
var mask_val = try o.builder.intConst(payload_llvm_ty, -1);
mask_val = try o.builder.castConst(.zext, mask_val, load_llvm_ty);
break :blk try fg.wip.bin(.@"and", shifted, mask_val.toValue(), "");
} else shifted;
return fg.wip.conv(.unneeded, anded, payload_llvm_ty, "");
}
/// Load a by-ref type by constructing a new alloca and performing a memcpy.