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
diff --git a/lib/Analysis/InstructionSimplify.cpp b/lib/Analysis/InstructionSimplify.cpp
index 1d4ff0f..f737354 100644
--- a/lib/Analysis/InstructionSimplify.cpp
+++ b/lib/Analysis/InstructionSimplify.cpp
@@ -593,6 +593,12 @@
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))
diff --git a/test/Transforms/InstSimplify/2010-12-20-Distribute.ll b/test/Transforms/InstSimplify/2010-12-20-Distribute.ll
index 60cef48..d20abd6 100644
--- a/test/Transforms/InstSimplify/2010-12-20-Distribute.ll
+++ b/test/Transforms/InstSimplify/2010-12-20-Distribute.ll
@@ -31,6 +31,26 @@
; CHECK: ret i32 %r
}
+define i32 @factorize4(i32 %x, i32 %y) {
+; CHECK: @factorize4
+ %sh = shl i32 %y, 1
+ %ml = mul i32 %sh, %x
+ %mr = mul i32 %x, %y
+ %s = sub i32 %ml, %mr
+ ret i32 %s
+; CHECK: ret i32 %mr
+}
+
+define i32 @factorize5(i32 %x, i32 %y) {
+; CHECK: @factorize5
+ %sh = mul i32 %y, 2
+ %ml = mul i32 %sh, %x
+ %mr = mul i32 %x, %y
+ %s = sub i32 %ml, %mr
+ ret i32 %s
+; CHECK: ret i32 %mr
+}
+
define i32 @expand(i32 %x) {
; CHECK: @expand
; ((X & 1) | 2) & 1 -> ((X & 1) & 1) | (2 & 1) -> (X & 1) | 0 -> X & 1