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void foo(int a) {
int a; // remove this line
}
1. generate random test.c file [csmith] 2. compile test.c to binary [clang] 3. modify generated test.c file [fix-csmi.sh] - Here we replace csmith.h header with necessery stuff to avoid header expansion while compiling to llvm in next step 4. compile to LLVMIR test.ll [clang] 5. run llvm2c and generate decompiled.c [llvm2c] 6. modify decompiled.c file [decom-fix-csmi.sh] - Here we add csmith.h include and fix types for functions from csmith.h 7. compile decompiled.c to binary [clang] 8. run compiled binaries and compare their outputs If something goes wrong at any point then all generated files are copied to tmp (for debug purpose). If we caught exception after running the compiled test.c then we continue to the next step.
Parse basic types are: - int - char - short - long - float - double - long double and correctly recognize whether a type is signed or unsigned.
from metadataTypeInfo
E.g. `int *` or `unsigned int*`
Which prints strings to the llvm:errs().
From https://lists.llvm.org/pipermail/cfe-dev/2013-January/027302.html: When a function has a struct parameter or return type, Clang may lower a struct parameter into... - a "byval" pointer (for a struct with several different members) - a vector (for a struct with a few float members) - two doubles (for a struct with two double members) - an i64 (for a struct with two i32 members) ... and possibly more variations. But there is no information in the metadata about types created in this way. Therefore, we detect the use of the struct type as an argument or return value of a function and do not reconstruct these types from the metadata.
Enable all (loop) passes from https://github.com/llvm-mirror/llvm/blob/master/lib/Transforms/IPO/PassManagerBuilder.cpp#L353-#L375: ```c if (EnableSimpleLoopUnswitch) { // The simple loop unswitch pass relies on separate cleanup passes. Schedule // them first so when we re-process a loop they run before other loop // passes. MPM.add(createLoopInstSimplifyPass()); MPM.add(createLoopSimplifyCFGPass()); } // Rotate Loop - disable header duplication at -Oz MPM.add(createLoopRotatePass(SizeLevel == 2 ? 0 : -1)); MPM.add(createLICMPass(LicmMssaOptCap, LicmMssaNoAccForPromotionCap)); if (EnableSimpleLoopUnswitch) MPM.add(createSimpleLoopUnswitchLegacyPass()); else MPM.add(createLoopUnswitchPass(SizeLevel || OptLevel < 3, DivergentTarget)); // FIXME: We break the loop pass pipeline here in order to do full // simplify-cfg. Eventually loop-simplifycfg should be enhanced to replace the // need for this. MPM.add(createCFGSimplificationPass()); addInstructionCombiningPass(MPM); // We resume loop passes creating a second loop pipeline here. MPM.add(createIndVarSimplifyPass()); // Canonicalize indvars MPM.add(createLoopIdiomPass()); // Recognize idioms like memset. ``` Test: ```bash clang -S -emit-llvm -Xclang -disable-O0-optnone simple-for-loop-second-latch.c -o simple-for-loop-second-latch-noopt.ll optpassPasses simple-for-loop-second-latch-noopt --loop-simplify --simplifycfg --loop-rotate --lcssa --licm --loop-unswitch --simplifycfg --instcombine --indvars old_llvm2c simple-for-loop-second-latch-noopt-opt == new_llvm2c simple-for-loop-second-latch-noopt ```
1. map LOOP with BRANCH instruction (condition) 2. transform BRANCH inst. to if's or doWhile constructs
First:
```c
goto head;
head:
...
do
goto head;
while( C );
```
transfrom into
```c
do
head
while( C );
Second:
Cache result from loopInfoAnalysis in particular function
and prepare for anonymous structs/unions Thanks @lzaoral for help!
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e.g., type function occurs as arg type or return type
I wrongly assume that llvm always generates positive loop conditions, e.g. if this is true, then iterate, but after -O3 optimisations, loop condition might be negated: if this is false, then continue to the next iteration. This new function will reverse the loop condition if the situation described above occurs! This might need a proper solution - this is hackery, because we do not replace the whole expression, just a printed character e.g. "<" -> ">=".
x = phi i32 [0, %beforeLoop] [%y, %fromLoop] ; coming from %fromLoop means we
are in a next iteration
before this commit:
x = 0;
do {
x = y;
loopBody(y, ...);
} while ( cond )
after this commit:
x = 0;
do {
loopBody(y, ...);
x = y;
} while ( cond )
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…eturn the m{ax,in}imum of the two operands.
My idea comes from https://reviews.llvm.org/D9293?id=&download=true
The expression:
call i8 @llvm.umin.i8(i8 %a, i8 %b)
is equivalent to
%1 = icmp ult i8 %a, %b
%2 = select i1 %1, i8 %a, i8 %b
This is what llvm2c outputs:
a < b ? a : b
…om the preheader block
This commit is probably the correct fix for what fd4978d was trying to address.
https://llvm.org/docs/LangRef.html#sext-to-instruction This is based on a fact that if you sext i1 cmp_result to i32, you can get either -1 or 0.
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Signed-off-by: Andrew V. Teylu <andrew.teylu@vector.com>
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