http://gcc.gnu.org/bugzilla/show_bug.cgi?id=60206
--- Comment #7 from wmi at google dot com --- After looking into the problem more, I found IVOPT may not be the root cause. Even if IVOPT create a memory operand using two registers, if only the following optimizations doesn't propagate the memory operand to an asm_operand, the problem will not happen. So I created another smallcase 2.c for which gcc at the head of trunk will report the same error. -fno-ivopts will not help here. gcc -v Target: x86_64-unknown-linux-gnu Configured with: ../src/configure --prefix=/usr/local/google/home/wmi/workarea/gcc-r208410/build/install Thread model: posix gcc version 4.9.0 20140307 (experimental) (GCC) gcc -O2 -fno-omit-frame-pointer -m32 -S 2.c 2.c: In function ‘foo’: 2.c:25:1: error: ‘asm’ operand has impossible constraints __asm__ ( ^ The problem will disappear after I use -fno-tree-ter and -fdisable-rtl-combine. These two phases could propagate a memory reference using a register into an asm operand with constraint "g", which make the registers used in asm stmt increase. For TER, TER of loads into input arguments is allowed. For combine, insn_invalid_p() will only check whether an asm operand will satisfy its constraint. However, neither TER nor combine check whether the propagation could make the registers in asm stmt exceed available register number.
