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optimize: 

void a(int x) { if (((1<<x)&8)==0) b(); }

into "x != 3", which occurs over 100 times in 403.gcc but in no
other program in llvm-test.

llvm-svn: 119922
This commit is contained in:
Chris Lattner 2010-11-21 06:44:42 +00:00
parent 0565e5c455
commit f7e896138e
3 changed files with 110 additions and 10 deletions
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8
llvm/lib/Target/README.txt
View File

@ -1699,14 +1699,6 @@ This should be optimized to a single compare. Testcase derived from gcc.
//===---------------------------------------------------------------------===//
Missed instcombine transformation:
void b();
void a(int x) { if (((1<<x)&8)==0) b(); }
The shift should be optimized out. Testcase derived from gcc.
//===---------------------------------------------------------------------===//
Missed instcombine or reassociate transformation:
int a(int a, int b) { return (a==12)&(b>47)&(b<58); }

74
llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
View File

@ -1744,14 +1744,84 @@ Instruction *InstCombiner::visitICmpInst(ICmpInst &I) {
// simplify this comparison. For example, (x&4) < 8 is always true.
switch (I.getPredicate()) {
default: llvm_unreachable("Unknown icmp opcode!");
case ICmpInst::ICMP_EQ:
case ICmpInst::ICMP_EQ: {
if (Op0Max.ult(Op1Min) || Op0Min.ugt(Op1Max))
return ReplaceInstUsesWith(I, ConstantInt::getFalse(I.getContext()));
// If all bits are known zero except for one, then we know at most one
// bit is set. If the comparison is against zero, then this is a check
// to see if *that* bit is set.
APInt Op0KnownZeroInverted = ~Op0KnownZero;
if (~Op1KnownZero == 0 && Op0KnownZeroInverted.isPowerOf2()) {
// If the LHS is an AND with the same constant, look through it.
Value *LHS = 0;
ConstantInt *LHSC = 0;
if (!match(Op0, m_And(m_Value(LHS), m_ConstantInt(LHSC))) ||
LHSC->getValue() != Op0KnownZeroInverted)
LHS = Op0;
// If the LHS is 1 << x, and we know the result is a power of 2 like 8,
// then turn "((1 << x)&8) == 0" into "x == 3".
Value *X = 0;
if (match(LHS, m_Shl(m_One(), m_Value(X)))) {
unsigned CmpVal = Op0KnownZeroInverted.countTrailingZeros();
return new ICmpInst(ICmpInst::ICMP_EQ, X,
ConstantInt::get(X->getType(), CmpVal));
}
// If the LHS is 8 >>u x, and we know the result is a power of 2 like 1,
// then turn "((8 >>u x)&1) == 0" into "x == 3".
ConstantInt *CI = 0;
if (Op0KnownZeroInverted == 1 &&
match(LHS, m_LShr(m_ConstantInt(CI), m_Value(X))) &&
CI->getValue().isPowerOf2()) {
unsigned CmpVal = CI->getValue().countTrailingZeros();
return new ICmpInst(ICmpInst::ICMP_EQ, X,
ConstantInt::get(X->getType(), CmpVal));
}
}
break;
case ICmpInst::ICMP_NE:
}
case ICmpInst::ICMP_NE: {
if (Op0Max.ult(Op1Min) || Op0Min.ugt(Op1Max))
return ReplaceInstUsesWith(I, ConstantInt::getTrue(I.getContext()));
// If all bits are known zero except for one, then we know at most one
// bit is set. If the comparison is against zero, then this is a check
// to see if *that* bit is set.
APInt Op0KnownZeroInverted = ~Op0KnownZero;
if (~Op1KnownZero == 0 && Op0KnownZeroInverted.isPowerOf2()) {
// If the LHS is an AND with the same constant, look through it.
Value *LHS = 0;
ConstantInt *LHSC = 0;
if (!match(Op0, m_And(m_Value(LHS), m_ConstantInt(LHSC))) ||
LHSC->getValue() != Op0KnownZeroInverted)
LHS = Op0;
// If the LHS is 1 << x, and we know the result is a power of 2 like 8,
// then turn "((1 << x)&8) != 0" into "x != 3".
Value *X = 0;
if (match(LHS, m_Shl(m_One(), m_Value(X)))) {
unsigned CmpVal = Op0KnownZeroInverted.countTrailingZeros();
return new ICmpInst(ICmpInst::ICMP_NE, X,
ConstantInt::get(X->getType(), CmpVal));
}
// If the LHS is 8 >>u x, and we know the result is a power of 2 like 1,
// then turn "((8 >>u x)&1) != 0" into "x != 3".
ConstantInt *CI = 0;
if (Op0KnownZeroInverted == 1 &&
match(LHS, m_LShr(m_ConstantInt(CI), m_Value(X))) &&
CI->getValue().isPowerOf2()) {
unsigned CmpVal = CI->getValue().countTrailingZeros();
return new ICmpInst(ICmpInst::ICMP_NE, X,
ConstantInt::get(X->getType(), CmpVal));
}
}
break;
}
case ICmpInst::ICMP_ULT:
if (Op0Max.ult(Op1Min)) // A <u B -> true if max(A) < min(B)
return ReplaceInstUsesWith(I, ConstantInt::getTrue(I.getContext()));

38
llvm/test/Transforms/InstCombine/icmp.ll
View File

@ -154,3 +154,41 @@ entry:
; CHECK: @test16
; CHECK: ret i1 undef
}
define i1 @test17(i32 %x) nounwind {
%shl = shl i32 1, %x
%and = and i32 %shl, 8
%cmp = icmp eq i32 %and, 0
ret i1 %cmp
; CHECK: @test17
; CHECK-NEXT: %cmp = icmp eq i32 %x, 3
}
define i1 @test18(i32 %x) nounwind {
%sh = lshr i32 8, %x
%and = and i32 %sh, 1
%cmp = icmp eq i32 %and, 0
ret i1 %cmp
; CHECK: @test18
; CHECK-NEXT: %cmp = icmp eq i32 %x, 3
}
define i1 @test19(i32 %x) nounwind {
%shl = shl i32 1, %x
%and = and i32 %shl, 8
%cmp = icmp eq i32 %and, 8
ret i1 %cmp
; CHECK: @test19
; CHECK-NEXT: %cmp = icmp ne i32 %x, 3
}
define i1 @test20(i32 %x) nounwind {
%shl = shl i32 1, %x
%and = and i32 %shl, 8
%cmp = icmp ne i32 %and, 0
ret i1 %cmp
; CHECK: @test20
; CHECK-NEXT: %cmp = icmp ne i32 %x, 3
}