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Add note about OptNone #35

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Jul 1, 2021
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Add note about OptNone #35

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20 changes: 13 additions & 7 deletions README.md
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Original file line number Diff line number Diff line change
Expand Up @@ -70,7 +70,7 @@ Before you can test it, you need to prepare an input file:

```bash
# Generate an LLVM test file
$LLVM_DIR/bin/clang -S -emit-llvm <source/dir/llvm/tutor/>inputs/input_for_hello.c -o input_for_hello.ll
$LLVM_DIR/bin/clang -O1 -S -emit-llvm <source/dir/llvm/tutor/>inputs/input_for_hello.c -o input_for_hello.ll
```

Finally, run **HelloWorld** with
Expand Down Expand Up @@ -250,15 +250,21 @@ LLVM passes work with LLVM IR files. You can generate one like this:
```bash
export LLVM_DIR=<installation/dir/of/llvm/12>
# Textual form
$LLVM_DIR/bin/clang -emit-llvm input.c -S -o out.ll
$LLVM_DIR/bin/clang -O1 -emit-llvm input.c -S -o out.ll
# Binary/bit-code form
$LLVM_DIR/bin/clang -emit-llvm input.c -o out.bc
$LLVM_DIR/bin/clang -O1 -emit-llvm input.c -o out.bc
```
It doesn't matter whether you choose the binary, `*.bc` (default), or textual
(`.ll`, requires the `-S` flag) form, but obviously the latter is more
human-readable. Similar logic applies to **opt** (by default it generates
`*.bc` files, use `-S` to generate an `*.ll` file instead).

Note that recent clang versions add the `OptNone` tag to all functions if either
no optimization level is specified or if `-O0` is specified. If you want to
compile at `-O0` you need to specify `-O0 -Xclang -disable-O0-optnone`.
Alternatively, you can specify `-O1` or higher. Otherwise the new pass
manager will register the pass but your pass will not be executed.

As noted [earlier](#llvm-plugins-as-shared-objecs), all examples in this file
use the `*.so` extension for pass plugins. When working on Mac OS, use
`*.dylib` instead.
Expand Down Expand Up @@ -291,7 +297,7 @@ need to choose which pass manager you want to use (see
```bash
export LLVM_DIR=<installation/dir/of/llvm/12>
# Generate an LLVM file to analyze
$LLVM_DIR/bin/clang -emit-llvm -c <source_dir>/inputs/input_for_cc.c -o input_for_cc.bc
$LLVM_DIR/bin/clang -O1 -emit-llvm -c <source_dir>/inputs/input_for_cc.c -o input_for_cc.bc
# Run the pass through opt - Legacy PM
$LLVM_DIR/bin/opt -load <build_dir>/lib/libOpcodeCounter.so -legacy-opcode-counter -analyze input_for_cc.bc
# Run the pass through opt - New PM
Expand Down Expand Up @@ -363,7 +369,7 @@ to test **InjectFuncCall**:
```bash
export LLVM_DIR=<installation/dir/of/llvm/12>
# Generate an LLVM file to analyze
$LLVM_DIR/bin/clang -emit-llvm -c <source_dir>/inputs/input_for_hello.c -o input_for_hello.bc
$LLVM_DIR/bin/clang -O1 -emit-llvm -c <source_dir>/inputs/input_for_hello.c -o input_for_hello.bc
# Run the pass through opt
$LLVM_DIR/bin/opt -load <build_dir>/lib/libInjectFuncCall.so -legacy-inject-func-call input_for_hello.bc -o instrumented.bin
```
Expand Down Expand Up @@ -434,7 +440,7 @@ to test **StaticCallCounter**:
```bash
export LLVM_DIR=<installation/dir/of/llvm/12>
# Generate an LLVM file to analyze
$LLVM_DIR/bin/clang -emit-llvm -c <source_dir>/inputs/input_for_cc.c -o input_for_cc.bc
$LLVM_DIR/bin/clang -O1 -emit-llvm -c <source_dir>/inputs/input_for_cc.c -o input_for_cc.bc
# Run the pass through opt - Legacy PM
$LLVM_DIR/bin/opt -load <build_dir>/lib/libStaticCallCounter.so -legacy-static-cc -analyze input_for_cc.bc
```
Expand Down Expand Up @@ -487,7 +493,7 @@ to test **DynamicCallCounter**:
```bash
export LLVM_DIR=<installation/dir/of/llvm/12>
# Generate an LLVM file to analyze
$LLVM_DIR/bin/clang -emit-llvm -c <source_dir>/inputs/input_for_cc.c -o input_for_cc.bc
$LLVM_DIR/bin/clang -O1 -emit-llvm -c <source_dir>/inputs/input_for_cc.c -o input_for_cc.bc
# Instrument the input file
$LLVM_DIR/bin/opt -load <build_dir>/lib/libDynamicCallCounter.so -legacy-dynamic-cc input_for_cc.bc -o instrumented_bin
```
Expand Down