> On Mar 25, 2016, at 2:23 PM, Akira Hatanaka via cfe-commits > <cfe-commits@lists.llvm.org> wrote: > >> >> On Mar 25, 2016, at 2:06 PM, David Majnemer via cfe-commits >> <cfe-commits@lists.llvm.org <mailto:cfe-commits@lists.llvm.org>> wrote: >> >> >> >> On Fri, Mar 25, 2016 at 12:57 PM, Akira Hatanaka via cfe-commits >> <cfe-commits@lists.llvm.org <mailto:cfe-commits@lists.llvm.org>> wrote: >> ahatanak created this revision. >> ahatanak added a reviewer: rjmccall. >> ahatanak added a subscriber: cfe-commits. >> >> r246985 made changes to give a higher alignment for exception objects on the >> grounds that Itanium says _Unwind_Exception should be "double-word" aligned >> and the structure is normally declared with __attribute__((aligned)) >> guaranteeing 16-byte alignment. It turns out that libc++abi doesn't declare >> the structure with __attribute__((aligned)) and therefore only guarantees >> 8-byte alignment on 32-bit and 64-bit platforms. This caused a crash in some >> cases when the backend emitted SIMD store instructions that requires 16-byte >> alignment (such as movaps). >> >> This patch makes ItaniumCXXABI::getAlignmentOfExnObject return an 8-byte >> alignment on Darwin to fix the crash. >> >> http://reviews.llvm.org/D18479 <http://reviews.llvm.org/D18479> >> >> Files: >> lib/CodeGen/ItaniumCXXABI.cpp >> test/CodeGenCXX/eh.cpp >> >> Index: test/CodeGenCXX/eh.cpp >> =================================================================== >> --- test/CodeGenCXX/eh.cpp >> +++ test/CodeGenCXX/eh.cpp >> @@ -448,5 +448,27 @@ >> } >> } >> >> +namespace test17 { >> +class BaseException { >> +private: >> + int a[4]; >> +public: >> + BaseException() {}; >> +}; >> + >> +class DerivedException: public BaseException { >> +}; >> + >> +int foo() { >> + throw DerivedException(); >> + // The alignment passed to memset is 8, not 16, on Darwin. >> + >> + // CHECK: [[T0:%.*]] = call i8* @__cxa_allocate_exception(i64 16) >> + // CHECK-NEXT: [[T1:%.*]] = bitcast i8* [[T0]] to >> %"class.test17::DerivedException"* >> + // CHECK-NEXT: [[T2:%.*]] = bitcast %"class.test17::DerivedException"* >> [[T1]] to i8* >> + // CHECK-NEXT: call void @llvm.memset.p0i8.i64(i8* [[T2]], i8 0, i64 16, >> i32 8, i1 false) >> +} >> +} >> + >> // CHECK: attributes [[NUW]] = { nounwind } >> // CHECK: attributes [[NR]] = { noreturn } >> Index: lib/CodeGen/ItaniumCXXABI.cpp >> =================================================================== >> --- lib/CodeGen/ItaniumCXXABI.cpp >> +++ lib/CodeGen/ItaniumCXXABI.cpp >> @@ -163,8 +163,17 @@ >> /// we assume that alignment here. (It's generally 16 bytes, but >> /// some targets overwrite it.) >> CharUnits getAlignmentOfExnObject() { >> - auto align = >> CGM.getContext().getTargetDefaultAlignForAttributeAligned(); >> - return CGM.getContext().toCharUnitsFromBits(align); >> + unsigned Align; >> + >> + // Alignment is 8 for darwin since libc++abi doesn't declare >> + // _Unwind_Exception with __attribute__((aligned)) and therefore doesn't >> + // guarantee 16-byte alignment. >> + if (CGM.getContext().getTargetInfo().getTriple().isOSDarwin()) >> >> What about Linux/FreeBSD targets which use libc++abi? >> > > Is there a way to detect whether libc++abi is used? >
I wasn’t planning to fix this for Linux or FreeBSD because I don’t know whether that is what people want. If the library being used returns an object that is 16-byte aligned (does libsupc++ return an aligned object?), my change would unnecessarily pessimize the code. >> + Align = 64; >> + else >> + Align = CGM.getContext().getTargetDefaultAlignForAttributeAligned(); >> + >> + return CGM.getContext().toCharUnitsFromBits(Align); >> } >> >> void emitRethrow(CodeGenFunction &CGF, bool isNoReturn) override; >> >> >> >> _______________________________________________ >> cfe-commits mailing list >> cfe-commits@lists.llvm.org <mailto:cfe-commits@lists.llvm.org> >> http://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-commits >> <http://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-commits> >> >> >> _______________________________________________ >> cfe-commits mailing list >> cfe-commits@lists.llvm.org <mailto:cfe-commits@lists.llvm.org> >> http://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-commits >> <http://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-commits> > _______________________________________________ > cfe-commits mailing list > cfe-commits@lists.llvm.org <mailto:cfe-commits@lists.llvm.org> > http://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-commits > <http://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-commits>
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