问题
While trying to see the SelectionDag nodes generated during the instruction selection phase using LLVM (built from sources with debug mode enabled), I am using the below command which is not creating Graphviz DOT file.
llc -view-isel-dags sum.bc
Instead it is creating sum.s file. Is there something I'm missing here?
sum.c
int sum(int x, int y) {
return x+y;
}
sum.bc
$ clang -emit-llvm sum.c -c -o sum.bc
LLVM information
$ llc -help-hidden | grep 'view-isel' -view-isel-dags - Pop up a window to show isel dags as they are selected
$ llvm-config --build-mode
Debug
回答1:
Guess the problem is with fast instruction selection which is enabled by default.
$ llc -debug sum.ll
Skipping pass 'X86 DAG->DAG Instruction Selection' on function sum
Changing optimization level for Function sum Before: -O2 ; After: -O0
FastISel is enabled
Disabling fastIsel resolved this problem.
$ llc -fast-isel=false -view-dag-combine1-dags sum.ll
来源：https://stackoverflow.com/questions/52055437/dot-file-not-genearting-for-view-isel-dags-option