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InstCombine: Make switch folding with equality compares more aggressive by trying instsimplify on the arm where we know the compared value.

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Stuff like "x == y ? y : x&y" now folds into "x&y".

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@132185 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Benjamin Kramer 2011-05-27 13:00:16 +00:00
parent f031d0977f
commit 17c1bb5d55
2 changed files with 94 additions and 15 deletions
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69
lib/Transforms/InstCombine/InstCombineSelect.cpp
View File

@ -278,6 +278,49 @@ Instruction *InstCombiner::FoldSelectIntoOp(SelectInst &SI, Value *TrueVal,
return 0;
}
/// SimplifyWithOpReplaced - See if V simplifies when its operand Op is
/// replaced with RepOp.
static Value *SimplifyWithOpReplaced(Value *V, Value *Op, Value *RepOp,
const TargetData *TD) {
// Trivial replacement.
if (V == Op)
return RepOp;
Instruction *I = dyn_cast<Instruction>(V);
if (!I)
return 0;
// If this is a binary operator, try to simplify it with the replaced op.
if (BinaryOperator *B = dyn_cast<BinaryOperator>(I)) {
if (B->getOperand(0) == Op)
return SimplifyBinOp(B->getOpcode(), RepOp, B->getOperand(1), TD);
if (B->getOperand(1) == Op)
return SimplifyBinOp(B->getOpcode(), B->getOperand(0), RepOp, TD);
}
// If all operands are constant after substituting Op for RepOp then we can
// constant fold the instruction.
if (Constant *CRepOp = dyn_cast<Constant>(RepOp)) {
// Build a list of all constant operands.
SmallVector<Constant*, 8> ConstOps;
for (unsigned i = 0, e = I->getNumOperands(); i != e; ++i) {
if (I->getOperand(i) == Op)
ConstOps.push_back(CRepOp);
else if (Constant *COp = dyn_cast<Constant>(I->getOperand(i)))
ConstOps.push_back(COp);
else
break;
}
// All operands were constants, fold it.
if (ConstOps.size() == I->getNumOperands())
return ConstantFoldInstOperands(I->getOpcode(), I->getType(),
ConstOps.data(), ConstOps.size(), TD);
}
return 0;
}
/// visitSelectInstWithICmp - Visit a SelectInst that has an
/// ICmpInst as its first operand.
///
@ -416,25 +459,21 @@ Instruction *InstCombiner::visitSelectInstWithICmp(SelectInst &SI,
}
}
if (CmpLHS == TrueVal && CmpRHS == FalseVal) {
// Transform (X == Y) ? X : Y -> Y
if (Pred == ICmpInst::ICMP_EQ)
// If we have an equality comparison then we know the value in one of the
// arms of the select. See if substituting this value into the arm and
// simplifying the result yields the same value as the other arm.
if (Pred == ICmpInst::ICMP_EQ) {
if (SimplifyWithOpReplaced(FalseVal, CmpLHS, CmpRHS, TD) == TrueVal ||
SimplifyWithOpReplaced(FalseVal, CmpRHS, CmpLHS, TD) == TrueVal)
return ReplaceInstUsesWith(SI, FalseVal);
// Transform (X != Y) ? X : Y -> X
if (Pred == ICmpInst::ICMP_NE)
} else if (Pred == ICmpInst::ICMP_NE) {
if (SimplifyWithOpReplaced(TrueVal, CmpLHS, CmpRHS, TD) == FalseVal ||
SimplifyWithOpReplaced(TrueVal, CmpRHS, CmpLHS, TD) == FalseVal)
return ReplaceInstUsesWith(SI, TrueVal);
/// NOTE: if we wanted to, this is where to detect integer MIN/MAX
} else if (CmpLHS == FalseVal && CmpRHS == TrueVal) {
// Transform (X == Y) ? Y : X -> X
if (Pred == ICmpInst::ICMP_EQ)
return ReplaceInstUsesWith(SI, FalseVal);
// Transform (X != Y) ? Y : X -> Y
if (Pred == ICmpInst::ICMP_NE)
return ReplaceInstUsesWith(SI, TrueVal);
/// NOTE: if we wanted to, this is where to detect integer MIN/MAX
}
// NOTE: if we wanted to, this is where to detect integer MIN/MAX
if (isa<Constant>(CmpRHS)) {
if (CmpLHS == TrueVal && Pred == ICmpInst::ICMP_EQ) {
// Transform (X == C) ? X : Y -> (X == C) ? C : Y

40
test/Transforms/InstCombine/select.ll
View File

@ -749,3 +749,43 @@ define i1 @test55(i1 %X, i32 %Y, i32 %Z) {
; CHECK: icmp eq
; CHECK: ret i1
}
define i32 @test56(i16 %x) nounwind {
%tobool = icmp eq i16 %x, 0
%conv = zext i16 %x to i32
%cond = select i1 %tobool, i32 0, i32 %conv
ret i32 %cond
; CHECK: @test56
; CHECK-NEXT: zext
; CHECK-NEXT: ret
}
define i32 @test57(i32 %x, i32 %y) nounwind {
%and = and i32 %x, %y
%tobool = icmp eq i32 %x, 0
%.and = select i1 %tobool, i32 0, i32 %and
ret i32 %.and
; CHECK: @test57
; CHECK-NEXT: and i32 %x, %y
; CHECK-NEXT: ret
}
define i32 @test58(i16 %x) nounwind {
%tobool = icmp ne i16 %x, 1
%conv = zext i16 %x to i32
%cond = select i1 %tobool, i32 %conv, i32 1
ret i32 %cond
; CHECK: @test58
; CHECK-NEXT: zext
; CHECK-NEXT: ret
}
define i32 @test59(i32 %x, i32 %y) nounwind {
%and = and i32 %x, %y
%tobool = icmp ne i32 %x, %y
%.and = select i1 %tobool, i32 %and, i32 %y
ret i32 %.and
; CHECK: @test59
; CHECK-NEXT: and i32 %x, %y
; CHECK-NEXT: ret
}