error: ran out of registers during register allocation

[kcc]

Bugzilla Link	11395
Version	trunk
OS	Linux
CC	@echristo,@efriedma-quic,@stoklund

Extended Description

Reproducer: % ./Release+Asserts/bin/llc z.o.ll error: ran out of registers during register allocation

Reduced from ffmpeg sources (with inline assembly) building with AddressSanitizer for x86_32

Observed on r144798

[echristo]

That's because the realignment will need another register.

[kcc]

But it indeed fails with -mstackrealign:

clang -m32 bug11395.c -c -mstackrealign bug11395.c:6:7: error: ran out of registers during register allocation

[kcc]

Hm. It compiles fine for me w/o -faddress-sanitizer.

[efriedma-quic]

clang -m32 -O1 -c -faddress-sanitizer -fno-omit-frame-pointer bug11395.c bug11395.c:6:7: error: ran out of registers during register allocation "int3" ^

The given example doesn't compile even without -faddress-sanitizer: it requires 7 registers, and there are only 6 registers available.

[kcc]

I had to extend the workaround (r147953). Before that revision codegen fails even if -faddress-sanitizer does not cause stack realignment.

% cat bug11395.c 

void foo_386(int *a, const int *b,
             unsigned int f, int d,
             int h, int *c, int *e, int *g)
{
  __asm__ volatile(
      "int3"
      : "+r"(a),
      "+r"(b),
      "+r"(c),
      "+m"(h)
      : "m"( d), "m"(g),
      "m"(e) , "m"(f)
      : "eax", "edx", "esi", "ecx"
      );
}

clang  -m32  -O1 -c -faddress-sanitizer    -fno-omit-frame-pointer bug11395.c 
bug11395.c:6:7: error: ran out of registers during register allocation
      "int3"
      ^
1 error generated.

[kcc]

r144962 added a workaround for AddressSanitizer.

[1ba3d143-a64b-4671-82b2-0b31cfb91709]

Err, no, I'm pretty sure the issue is that there's an inline asm which requires 7 registers in a function using stack realignment (which means there are only 6 registers available).

Interesting, bugpoint changes it from one to the other.

[efriedma-quic]

This is another case where "m" constraints referring to alloca objects get their own register instead of using the stack/frame pointer.

Err, no, I'm pretty sure the issue is that there's an inline asm which requires 7 registers in a function using stack realignment (which means there are only 6 registers available).

[llvmbot]

further reduced testcase

[1ba3d143-a64b-4671-82b2-0b31cfb91709]

This is another case where "m" constraints referring to alloca objects get their own register instead of using the stack/frame pointer.

[kcc]

.ll file

[1ba3d143-a64b-4671-82b2-0b31cfb91709]

Attachment is missing.

[nickdesaulniers]

$ wget https://user-images.githubusercontent.com/1789297/143744272-1d1952a5-f8f5-4b25-8149-1ee230dd0740.gz
$ mv 143744272-1d1952a5-f8f5-4b25-8149-1ee230dd0740 foo.ll
$ llc foo.ll
llc: error: llc: foo.ll:45:68: error: expected comma after getelementptr's type
  %mlp_filter_channel = getelementptr inbounds %struct.DSPContext* %c, i32 0, i32 131
                                                                   ^
$ wget wget https://user-images.githubusercontent.com/60944935/143744271-18fd6c63-6f7f-4364-bf90-3d79f2d857a2.gz
$ gunzip 143744271-18fd6c63-6f7f-4364-bf90-3d79f2d857a2.gz
$ mv 143744271-18fd6c63-6f7f-4364-bf90-3d79f2d857a2 foo.ll
$ llc foo.ll 
llc: error: llc: foo.ll:8:55: error: expected comma after getelementptr's type
  %MyAlloca4.sub = getelementptr inbounds [88 x i32]* %MyAlloca4, i32 0, i32 0
                                                      ^
$ clang  -m32  -O1 -c -fsanitize=address    -fno-omit-frame-pointer bug11395.c  
bug11395.c:6:7: error: inline assembly requires more registers than available
      "int3"
      ^
1 error generated.

So the .ll test files are outdated, but the issue is still reproducible today w/ clang-15.

[llvmbot]

@llvm/issue-subscribers-backend-x86

[nickdesaulniers]

$ clang -m32 bug11395.c -c -mstackrealign

actually causes an ICE in clang-15:

clang: /android0/llvm-project/llvm/lib/CodeGen/RegAllocFast.cpp:921: void (anonymous namespace)::RegAllocFast::defineVirtReg(llvm::MachineInstr &, unsigned int, llvm::Register, bool): Assertion `PhysReg != 0 && "Register not assigned"' failed.
...
#10 0x00000000033e285d (anonymous namespace)::RegAllocFast::defineVirtReg(llvm::MachineInstr&, unsigned int, llvm::Register, bool) RegAllocFast.cpp:0:0
#11 0x00000000033df176 (anonymous namespace)::RegAllocFast::allocateInstruction(llvm::MachineInstr&) RegAllocFast.cpp:0:0
#12 0x00000000033dbd1b (anonymous namespace)::RegAllocFast::runOnMachineFunction(llvm::MachineFunction&) RegAllocFast.cpp:0:0
#13 0x00000000030e003d llvm::MachineFunctionPass::runOnFunction(llvm::Function&) (/android0/llvm-project/llvm/build/bin/clang-15+0x30e003d)