[release/6.0] Fix build with Clang 13 #63314
Conversation
The clang 13 optimizer started to assume that "this" pointer is always properly aligned. That lead to elimination of some code that was actually needed. It also takes pointer aliasing rules more strictly in one place in jit. That caused the optimizer to falsely assume that a callee with an argument passed by reference is not modifying that argument and used a stale copy of the original value at the caller site. This change fixes both of the issues. With this fix, runtime compiled using clang 13 seems to be fully functional.
janvorli
added
Servicing-consider
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Tagging subscribers to this area: @dotnet/area-meta Issue DetailsPort fix of build using Clang 13 to release/6.0. Customer ImpactThe recently released Clang 13 is stricter in warnings and it also started to apply assumption that TestingLocal builds of release and debug versions using clang 9 and clang 13 RiskLow, there are no functional changes and the fix has been in main branch for about a month.
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cc: @omajid |
leecow
added
Servicing-approved
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Hey, @janvorli, do you think this is worth backporting to 3.1 and 5.0 as well? I just hit this in 3.1 too, and and this smaller patch seems to be sufficent for me: diff --git a/src/inc/corhlpr.h b/src/inc/corhlpr.h
index 5b263a5382..c512069fca 100644
--- a/src/inc/corhlpr.h
+++ b/src/inc/corhlpr.h
@@ -335,7 +335,7 @@ struct COR_ILMETHOD_SECT
const COR_ILMETHOD_SECT* Next() const
{
if (!More()) return(0);
- return ((COR_ILMETHOD_SECT*)(((BYTE *)this) + DataSize()))->Align();
+ return ((COR_ILMETHOD_SECT*)Align(((BYTE *)this) + DataSize()));
}
const BYTE* Data() const
@@ -373,9 +373,9 @@ struct COR_ILMETHOD_SECT
return((AsSmall()->Kind & CorILMethod_Sect_FatFormat) != 0);
}
- const COR_ILMETHOD_SECT* Align() const
+ static const void* Align(const void* p)
{
- return((COR_ILMETHOD_SECT*) ((((UINT_PTR) this) + 3) & ~3));
+ return((void*) ((((UINT_PTR) p) + 3) & ~3));
}
protected:
@@ -578,7 +578,7 @@ typedef struct tagCOR_ILMETHOD_FAT : IMAGE_COR_ILMETHOD_FAT
const COR_ILMETHOD_SECT* GetSect() const {
if (!More()) return (0);
- return(((COR_ILMETHOD_SECT*) (GetCode() + GetCodeSize()))->Align());
+ return(((COR_ILMETHOD_SECT*) COR_ILMETHOD_SECT::Align(GetCode() + GetCodeSize())));
}
} COR_ILMETHOD_FAT;
diff --git a/src/jit/bitsetasshortlong.h b/src/jit/bitsetasshortlong.h
index 17e0e3a69c..0c40283ce5 100644
--- a/src/jit/bitsetasshortlong.h
+++ b/src/jit/bitsetasshortlong.h
@@ -346,7 +346,7 @@ public:
{
if (IsShort(env))
{
- (size_t&)out = (size_t)out & ((size_t)gen | (size_t)in);
+ out = (BitSetShortLongRep)((size_t)out & ((size_t)gen | (size_t)in));
}
else
{
@@ -362,7 +362,7 @@ public:
{
if (IsShort(env))
{
- (size_t&)in = (size_t)use | ((size_t)out & ~(size_t)def);
+ in = (BitSetShortLongRep)((size_t)use | ((size_t)out & ~(size_t)def));
}
else
{ |
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@omajid so the compiler warning disabling was not needed in 3.1? |
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I just built a fresh clone of coreclr 3.1 with only that smaller patch and it seems to build (I didn't run any tests, though). Git history shows that we turned off |
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The other part of the change was just to silence the warnings, so if the compiler doesn't complain, we are good. |
ghost
locked as resolved and limited conversation to collaborators
Port fix of build using Clang 13 to release/6.0.
Customer Impact
The recently released Clang 13 is stricter in warnings and it also started to apply assumption that
thispointer is always aligned to the natural alignment of the object. These break compilation of .NET 6 e.g. on Fedora 35 where Clang 13 is the one installed. This issue was reported by Redhat developers.Testing
Local builds of release and debug versions using clang 9 and clang 13
Risk
Low, there are no functional changes and the fix has been in main branch for about a month.