[PATCH] InstCombine: merge constants in both operands of icmp.
Benjamin Kramer
benny.kra at gmail.com
Tue Mar 25 12:19:38 PDT 2014
On 25.03.2014, at 16:33, Erik Verbruggen <erik.verbruggen at me.com> wrote:
> From 5290972d0df27a30a789a3c7a56a794e4bdf059d Mon Sep 17 00:00:00 2001
> From: Erik Verbruggen <erik.verbruggen at me.com>
> Date: Mon, 17 Mar 2014 15:26:08 +0100
> Subject: [PATCH] InstCombine: merge constants in both operands of icmp.
>
> E.g.: x + 10 < 0 --> x < -10 (if add has nsw)
> x - 10 < 0 --> x < 10 (if sub has nsw)
> ---
> lib/Target/README.txt | 12 -----
> lib/Transforms/InstCombine/InstCombine.h | 2 +
> lib/Transforms/InstCombine/InstCombineCompares.cpp | 33 ++++++++++++++
> test/Transforms/InstCombine/icmp.ll | 53 ++++++++++++++++++++++
> 4 files changed, 88 insertions(+), 12 deletions(-)
>
> diff --git a/lib/Target/README.txt b/lib/Target/README.txt
> index a9aab86..4ecacf9 100644
> --- a/lib/Target/README.txt
> +++ b/lib/Target/README.txt
> @@ -930,18 +930,6 @@ optimized with "clang -emit-llvm-bc | opt -std-compile-opts".
>
> //===---------------------------------------------------------------------===//
>
> -int g(int x) { return (x - 10) < 0; }
> -Should combine to "x <= 9" (the sub has nsw). Currently not
> -optimized with "clang -emit-llvm-bc | opt -std-compile-opts".
> -
> -//===---------------------------------------------------------------------===//
> -
> -int g(int x) { return (x + 10) < 0; }
> -Should combine to "x < -10" (the add has nsw). Currently not
> -optimized with "clang -emit-llvm-bc | opt -std-compile-opts".
> -
> -//===---------------------------------------------------------------------===//
> -
> int f(int i, int j) { return i < j + 1; }
> int g(int i, int j) { return j > i - 1; }
> Should combine to "i <= j" (the add/sub has nsw). Currently not
> diff --git a/lib/Transforms/InstCombine/InstCombine.h b/lib/Transforms/InstCombine/InstCombine.h
> index 822e146..bc646db 100644
> --- a/lib/Transforms/InstCombine/InstCombine.h
> +++ b/lib/Transforms/InstCombine/InstCombine.h
> @@ -169,6 +169,8 @@ public:
> ConstantInt *DivRHS);
> Instruction *FoldICmpAddOpCst(Instruction &ICI, Value *X, ConstantInt *CI,
> ICmpInst::Predicate Pred);
> + Instruction *FoldIcmpBinopConst(BinaryOperator *BO, ConstantInt *Cst,
> + ICmpInst::Predicate Pred);
> Instruction *FoldGEPICmp(GEPOperator *GEPLHS, Value *RHS,
> ICmpInst::Predicate Cond, Instruction &I);
> Instruction *FoldShiftByConstant(Value *Op0, ConstantInt *Op1,
> diff --git a/lib/Transforms/InstCombine/InstCombineCompares.cpp b/lib/Transforms/InstCombine/InstCombineCompares.cpp
> index 8c0ad52..fd365ea 100644
> --- a/lib/Transforms/InstCombine/InstCombineCompares.cpp
> +++ b/lib/Transforms/InstCombine/InstCombineCompares.cpp
> @@ -795,6 +795,29 @@ Instruction *InstCombiner::FoldICmpAddOpCst(Instruction &ICI,
> return new ICmpInst(ICmpInst::ICMP_SLT, X, ConstantExpr::getSub(SMax, C));
> }
>
> +Instruction *InstCombiner::FoldIcmpBinopConst(BinaryOperator *BO,
> + ConstantInt *Cst,
> + ICmpInst::Predicate Pred) {
> + Value *X; ConstantInt *Cst2;
> + if (match(BO, m_Add(m_Value(X), m_ConstantInt(Cst2))) ||
> + match(BO, m_Add(m_ConstantInt(Cst2), m_Value(X)))) {
This case should never happen, InstCombine canonicalizes constants to the right side.
> + if (!BO->hasNoSignedWrap())
> + return nullptr;
> + // Transform:
> + // icmp X+Cst2, Cst
> + // or:
> + // icmp Cst2+X, Cst
> + // into:
> + // icmp X, Cst-Cst2
> + // when Cst-Cst2 does not overflow
> + bool overflow;
> + APInt newCst = Cst->getValue().ssub_ov(Cst2->getValue(), overflow);
I'd prefer to use consistent PascalCase variable names.
> + if (!overflow)
> + return new ICmpInst(Pred, X, ConstantInt::get(Cst->getType(), newCst));
> + }
> + return nullptr;
> +}
> +
> /// FoldICmpDivCst - Fold "icmp pred, ([su]div X, DivRHS), CmpRHS" where DivRHS
> /// and CmpRHS are both known to be integer constants.
> Instruction *InstCombiner::FoldICmpDivCst(ICmpInst &ICI, BinaryOperator *DivI,
> @@ -3008,6 +3031,16 @@ Instruction *InstCombiner::visitICmpInst(ICmpInst &I) {
> // icmp X, X+Cst
> if (match(Op1, m_Add(m_Value(X), m_ConstantInt(Cst))) && Op0 == X)
> return FoldICmpAddOpCst(I, X, Cst, I.getSwappedPredicate());
> +
> + if (match(Op1, m_ConstantInt(Cst))) {
> + if (BinaryOperator *BO = dyn_cast<BinaryOperator>(Op0))
> + // icmp binop, Cst
> + return FoldIcmpBinopConst(BO, Cst, I.getPredicate());
> + } else if (match(Op0, m_ConstantInt(Cst))) {
> + if (BinaryOperator *BO = dyn_cast<BinaryOperator>(Op1))
> + // icmp Cst, binop
> + return FoldIcmpBinopConst(BO, Cst, I.getInversePredicate());
> + }
> }
> return Changed ? &I : 0;
> }
> diff --git a/test/Transforms/InstCombine/icmp.ll b/test/Transforms/InstCombine/icmp.ll
> index 12a4744..a78d010 100644
> --- a/test/Transforms/InstCombine/icmp.ll
> +++ b/test/Transforms/InstCombine/icmp.ll
> @@ -1356,3 +1356,56 @@ define i1 @icmp_ashr_ashr_ne(i32 %a, i32 %b) nounwind {
> %z = icmp ne i32 %x, %y
> ret i1 %z
> }
> +
> +; CHECK-LABEL: icmp_add_const_const1
> +; CHECK: %cmp = icmp slt i32 %x, -10
> +; CHEKC-NOT: %add = add nsw i32 %x, 10
CHEKC?
- Ben
> +define i32 @icmp_add_const_const1(i32 %x) nounwind ssp uwtable {
> +entry:
> + %add = add nsw i32 %x, 10
> + %cmp = icmp slt i32 %add, 0
> + %conv = zext i1 %cmp to i32
> + ret i32 %conv
> +}
> +
> +; CHECK-LABEL: icmp_add_const_const2
> +; CHECK: %cmp = icmp slt i32 %x, -10
> +; CHEKC-NOT: %add = add nsw i32 %x, 10
> +define i32 @icmp_add_const_const2(i32 %x) nounwind ssp uwtable {
> +entry:
> + %add = add nsw i32 %x, 10
> + %cmp = icmp sgt i32 0, %add
> + %conv = zext i1 %cmp to i32
> + ret i32 %conv
> +}
> +
> +; CHECK-LABEL: icmp_add_const_intmin
> +; CHECK: %cmp = icmp ne i32 %x, 2147483638
> +define i32 @icmp_add_const_intmin(i32 %x) nounwind ssp uwtable {
> +entry:
> + %add = add nsw i32 %x, 10
> + %cmp = icmp sgt i32 %add, -2147483648
> + %conv = zext i1 %cmp to i32
> + ret i32 %conv
> +}
> +
> +; CHECK-LABEL: icmp_add_const_intmax
> +; CHECK: %cmp = icmp ne i32 %x, 2147483637
> +define i32 @icmp_add_const_intmax(i32 %x) nounwind ssp uwtable {
> +entry:
> + %add = add nsw i32 %x, 10
> + %cmp = icmp slt i32 %add, 2147483647
> + %conv = zext i1 %cmp to i32
> + ret i32 %conv
> +}
> +
> +; CHECK-LABEL: icmp_sub_const_const
> +; CHECK: %cmp = icmp slt i32 %x, 10
> +; CHECK-NOT: %sub = add nsw i32 %x, -10
> +define i32 @icmp_sub_const_const(i32 %x) nounwind ssp uwtable {
> +entry:
> + %sub = sub nsw i32 %x, 10
> + %cmp = icmp slt i32 %sub, 0
> + %conv = zext i1 %cmp to i32
> + ret i32 %conv
> +}
> --
> 1.8.5.4
>
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