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InstCombine: merge constants in both operands of icmp. 

Transform:
    icmp X+Cst2, Cst
into:
    icmp X, Cst-Cst2
when Cst-Cst2 does not overflow, and the add has nsw.

llvm-svn: 204912
This commit is contained in:
Erik Verbruggen 2014-03-27 11:16:05 +00:00
parent d897b564ca
commit 59a1219846
3 changed files with 66 additions and 12 deletions
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12
llvm/lib/Target/README.txt
View File

@ -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

13
llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
View File

@ -3008,6 +3008,19 @@ 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());
ConstantInt *Cst2;
if (match(Op1, m_ConstantInt(Cst)) &&
match(Op0, m_Add(m_Value(X), m_ConstantInt(Cst2))) &&
cast<BinaryOperator>(Op0)->hasNoSignedWrap()) {
// icmp X+Cst2, Cst --> icmp X, Cst-Cst2
// iff Cst-Cst2 does not overflow
bool Overflow;
APInt NewCst = Cst->getValue().ssub_ov(Cst2->getValue(), Overflow);
if (!Overflow)
return new ICmpInst(I.getPredicate(), X,
ConstantInt::get(Cst->getType(), NewCst));
}
}
return Changed ? &I : 0;
}

53
llvm/test/Transforms/InstCombine/icmp.ll
View File

@ -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
; CHECK-NOT: %add = add nsw i32 %x, 10
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
; CHECK-NOT: %add = add nsw i32 %x, 10
define i32 @icmp_add_const_const2(i32 %x) nounwind ssp uwtable {
entry:
%add = add nsw i32 10, %x
%cmp = icmp sgt i32 0, %add
%conv = zext i1 %cmp to i32
ret i32 %conv
}
; CHECK-LABEL: icmp_add_const_const3
; CHECK: %cmp = icmp slt i32 %x, 20
; CHECK-NOT: %sub = add nsw i32 %x, -10
define i32 @icmp_add_const_const3(i32 %x) nounwind ssp uwtable {
entry:
%add = add nsw i32 -10, %x
%cmp = icmp sgt i32 10, %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
}