diff options
| author | Duncan Sands <baldrick@free.fr> | 2011-01-18 09:24:58 +0000 |
|---|---|---|
| committer | Duncan Sands <baldrick@free.fr> | 2011-01-18 09:24:58 +0000 |
| commit | fe02c69f84ad52d42be934e4fe702f03e4991a6a (patch) | |
| tree | aa3ac73de8b775633dc315afb6b202b8ed74770e /lib/Analysis/InstructionSimplify.cpp | |
| parent | 908d8e82b5cc19d1a0a55a5fbc9dfd87359d726e (diff) | |
Simplify (X<<1)-X into X. According to my auto-simplier this is the most common missed
simplification in fully optimized code. It occurs sporadically in the testsuite, and
many times in 403.gcc: the final bitcode has 131 fewer subtractions after this change.
The reason that the multiplies are not eliminated is the same reason that instcombine
did not catch this: they are used by other instructions (instcombine catches this with
a more general transform which in general is only profitable if the operands have only
one use).
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@123754 91177308-0d34-0410-b5e6-96231b3b80d8
Diffstat (limited to 'lib/Analysis/InstructionSimplify.cpp')
| -rw-r--r-- | lib/Analysis/InstructionSimplify.cpp | 6 |
1 files changed, 6 insertions, 0 deletions
diff --git a/lib/Analysis/InstructionSimplify.cpp b/lib/Analysis/InstructionSimplify.cpp index 1d4ff0fc9e..f737354b36 100644 --- a/lib/Analysis/InstructionSimplify.cpp +++ b/lib/Analysis/InstructionSimplify.cpp @@ -593,6 +593,12 @@ static Value *SimplifySubInst(Value *Op0, Value *Op1, bool isNSW, bool isNUW, match(Op0, m_Add(m_Specific(Op1), m_Value(X)))) return X; + // (X*2) - X -> X + // (X<<1) - X -> X + if (match(Op0, m_Mul(m_Specific(Op1), m_ConstantInt<2>())) || + match(Op0, m_Shl(m_Specific(Op1), m_One()))) + return Op1; + // i1 sub -> xor. if (MaxRecurse && Op0->getType()->isIntegerTy(1)) if (Value *V = SimplifyXorInst(Op0, Op1, TD, DT, MaxRecurse-1)) |