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[clang][AArch64] Avoid a crash when a non-reserved register is used #117419

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Merged
merged 3 commits into from
Dec 6, 2024
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[clang][AArch64] Avoid a crash when a non-reserved register is used #117419

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54fc788
[clang][AArch64] Avoid a crash when a non-reserved register is used
igorkudrin Nov 23, 2024
1f1fe3d
fixup: Improve tests
igorkudrin Nov 26, 2024
255ac95
fixup: also check w* registers
igorkudrin Dec 6, 2024
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18 changes: 14 additions & 4 deletions clang/lib/Basic/Targets/AArch64.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -232,13 +232,23 @@ bool AArch64TargetInfo::validateTarget(DiagnosticsEngine &Diags) const {

bool AArch64TargetInfo::validateGlobalRegisterVariable(
StringRef RegName, unsigned RegSize, bool &HasSizeMismatch) const {
if ((RegName == "sp") || RegName.starts_with("x")) {
HasSizeMismatch = RegSize != 64;
return true;
} else if (RegName.starts_with("w")) {
if (RegName.starts_with("w")) {
HasSizeMismatch = RegSize != 32;
return true;
}
if (RegName == "sp") {
HasSizeMismatch = RegSize != 64;
return true;
}
if (RegName.starts_with("x")) {
HasSizeMismatch = RegSize != 64;
// Check if the register is reserved. See also
// AArch64TargetLowering::getRegisterByName().
return RegName == "x0" ||
(RegName == "x18" &&
llvm::AArch64::isX18ReservedByDefault(getTriple())) ||
getTargetOpts().FeatureMap.lookup(("reserve-" + RegName).str());
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@kawashima-fj kawashima-fj Nov 26, 2024

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To avoid the fatal error: error in backend: Invalid register name "x??" error in #109778, this check is sufficient.

I think the original purpose of rejecting a global register variable associated with a non-reserved register is to avoid unintended register use. w?? registers are lower half bits of the corresponding x?? registers. So when x?? register is not reserved, should we reject a global register variable associated with the corresponding w???

For this purpose, maybe the backend should also check w?? registers. Actually, old backend code checked w?? regsters.

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@igorkudrin igorkudrin Dec 6, 2024

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Thanks! Since this patch is focused on fixing the crash, it doesn't seem appropriate to make AArch64TargetLowering::getRegisterByName() more restrictive here. However, I added checks for w?? registers in AArch64TargetInfo::validateGlobalRegisterVariable() and corresponding tests.

}
return false;
}

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4 changes: 3 additions & 1 deletion clang/test/Sema/aarch64-fixed-global-register.c
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@@ -1,4 +1,6 @@
// RUN: %clang_cc1 -triple aarch64-unknown-none-gnu %s -verify -fsyntax-only
// RUN: %clang_cc1 -triple aarch64-unknown-none-gnu %s -target-feature +reserve-x4 -target-feature +reserve-x15 -verify -fsyntax-only

register char i1 __asm__ ("x15"); // expected-error {{size of register 'x15' does not match variable size}}
register long long l2 __asm__ ("w14"); // expected-error {{size of register 'w14' does not match variable size}}
register long x3 __asm__ ("x3"); // expected-error {{register 'x3' unsuitable for global register variables on this target}}
register long x4 __asm__ ("x4");
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