[llvm-commits] [llvm] r122182 - in /llvm/trunk: lib/Target/README.txt lib/Transforms/InstCombine/InstCombineCompares.cpp test/Transforms/InstCombine/overflow.ll
Chris Lattner
sabre at nondot.org
Sun Dec 19 11:37:53 PST 2010
Author: lattner
Date: Sun Dec 19 13:37:52 2010
New Revision: 122182
URL: http://llvm.org/viewvc/llvm-project?rev=122182&view=rev
Log:
recognize an unsigned add with overflow idiom into uadd.
This resolves a README entry and technically resolves PR4916,
but we still get poor code for the testcase in that PR because
GVN isn't CSE'ing uadd with add, filed as PR8817.
Previously we got:
_test7: ## @test7
addq %rsi, %rdi
cmpq %rdi, %rsi
movl $42, %eax
cmovaq %rsi, %rax
ret
Now we get:
_test7: ## @test7
addq %rsi, %rdi
movl $42, %eax
cmovbq %rsi, %rax
ret
Modified:
llvm/trunk/lib/Target/README.txt
llvm/trunk/lib/Transforms/InstCombine/InstCombineCompares.cpp
llvm/trunk/test/Transforms/InstCombine/overflow.ll
Modified: llvm/trunk/lib/Target/README.txt
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Target/README.txt?rev=122182&r1=122181&r2=122182&view=diff
==============================================================================
--- llvm/trunk/lib/Target/README.txt (original)
+++ llvm/trunk/lib/Target/README.txt Sun Dec 19 13:37:52 2010
@@ -74,26 +74,7 @@
//===---------------------------------------------------------------------===//
We should recognized various "overflow detection" idioms and translate them into
-llvm.uadd.with.overflow and similar intrinsics. For example, we compile this:
-
-size_t add(size_t a,size_t b) {
- if (a+b<a)
- exit(0);
- return a+b;
-}
-
-into:
-
- addq %rdi, %rbx
- cmpq %rdi, %rbx
- jae LBB0_2
-
-when it would be better to generate:
-
- addq %rdi, %rbx
- jno LBB0_2
-
-Apparently some version of GCC knows this. Here is a multiply idiom:
+llvm.uadd.with.overflow and similar intrinsics. Here is a multiply idiom:
unsigned int mul(unsigned int a,unsigned int b) {
if ((unsigned long long)a*b>0xffffffff)
Modified: llvm/trunk/lib/Transforms/InstCombine/InstCombineCompares.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/InstCombine/InstCombineCompares.cpp?rev=122182&r1=122181&r2=122182&view=diff
==============================================================================
--- llvm/trunk/lib/Transforms/InstCombine/InstCombineCompares.cpp (original)
+++ llvm/trunk/lib/Transforms/InstCombine/InstCombineCompares.cpp Sun Dec 19 13:37:52 2010
@@ -1648,7 +1648,7 @@
// Put the new code above the original add, in case there are any uses of the
// add between the add and the compare.
- Builder->SetInsertPoint(OrigAdd->getParent(), BasicBlock::iterator(OrigAdd));
+ Builder->SetInsertPoint(OrigAdd);
Value *TruncA = Builder->CreateTrunc(A, NewType, A->getName()+".trunc");
Value *TruncB = Builder->CreateTrunc(B, NewType, B->getName()+".trunc");
@@ -1664,6 +1664,35 @@
return ExtractValueInst::Create(Call, 1, "sadd.overflow");
}
+static Instruction *ProcessUAddIdiom(Instruction &I, Value *OrigAddV,
+ InstCombiner &IC) {
+ // Don't bother doing this transformation for pointers, don't do it for
+ // vectors.
+ if (!isa<IntegerType>(OrigAddV->getType())) return 0;
+
+ // If the add is a constant expr, then we don't bother transforming it.
+ Instruction *OrigAdd = dyn_cast<Instruction>(OrigAddV);
+ if (OrigAdd == 0) return 0;
+
+ Value *LHS = OrigAdd->getOperand(0), *RHS = OrigAdd->getOperand(1);
+
+ // Put the new code above the original add, in case there are any uses of the
+ // add between the add and the compare.
+ InstCombiner::BuilderTy *Builder = IC.Builder;
+ Builder->SetInsertPoint(OrigAdd);
+
+ Module *M = I.getParent()->getParent()->getParent();
+ const Type *Ty = LHS->getType();
+ Value *F = Intrinsic::getDeclaration(M, Intrinsic::uadd_with_overflow, &Ty,1);
+ CallInst *Call = Builder->CreateCall2(F, LHS, RHS, "uadd");
+ Value *Add = Builder->CreateExtractValue(Call, 0);
+
+ IC.ReplaceInstUsesWith(*OrigAdd, Add);
+
+ // The original icmp gets replaced with the overflow value.
+ return ExtractValueInst::Create(Call, 1, "uadd.overflow");
+}
+
Instruction *InstCombiner::visitICmpInst(ICmpInst &I) {
bool Changed = false;
@@ -1726,11 +1755,11 @@
}
unsigned BitWidth = 0;
- if (TD)
- BitWidth = TD->getTypeSizeInBits(Ty->getScalarType());
- else if (Ty->isIntOrIntVectorTy())
+ if (Ty->isIntOrIntVectorTy())
BitWidth = Ty->getScalarSizeInBits();
-
+ else if (TD) // Pointers require TD info to get their size.
+ BitWidth = TD->getTypeSizeInBits(Ty->getScalarType());
+
bool isSignBit = false;
// See if we are doing a comparison with a constant.
@@ -2225,6 +2254,22 @@
if (match(Op0, m_Not(m_Value(A))) &&
match(Op1, m_Not(m_Value(B))))
return new ICmpInst(I.getPredicate(), B, A);
+
+ // (a+b) <u a --> llvm.uadd.with.overflow.
+ // (a+b) <u b --> llvm.uadd.with.overflow.
+ if (I.getPredicate() == ICmpInst::ICMP_ULT &&
+ match(Op0, m_Add(m_Value(A), m_Value(B))) &&
+ (Op1 == A || Op1 == B))
+ if (Instruction *R = ProcessUAddIdiom(I, Op0, *this))
+ return R;
+
+ // a >u (a+b) --> llvm.uadd.with.overflow.
+ // b >u (a+b) --> llvm.uadd.with.overflow.
+ if (I.getPredicate() == ICmpInst::ICMP_UGT &&
+ match(Op1, m_Add(m_Value(A), m_Value(B))) &&
+ (Op0 == A || Op0 == B))
+ if (Instruction *R = ProcessUAddIdiom(I, Op1, *this))
+ return R;
}
if (I.isEquality()) {
Modified: llvm/trunk/test/Transforms/InstCombine/overflow.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/InstCombine/overflow.ll?rev=122182&r1=122181&r2=122182&view=diff
==============================================================================
--- llvm/trunk/test/Transforms/InstCombine/overflow.ll (original)
+++ llvm/trunk/test/Transforms/InstCombine/overflow.ll Sun Dec 19 13:37:52 2010
@@ -97,3 +97,37 @@
; CHECK: ret i8
}
+; CHECK: @test5
+; CHECK: llvm.uadd.with.overflow
+; CHECK: ret i64
+define i64 @test5(i64 %a, i64 %b) nounwind ssp {
+entry:
+ %add = add i64 %b, %a
+ %cmp = icmp ult i64 %add, %a
+ %Q = select i1 %cmp, i64 %b, i64 42
+ ret i64 %Q
+}
+
+; CHECK: @test6
+; CHECK: llvm.uadd.with.overflow
+; CHECK: ret i64
+define i64 @test6(i64 %a, i64 %b) nounwind ssp {
+entry:
+ %add = add i64 %b, %a
+ %cmp = icmp ult i64 %add, %b
+ %Q = select i1 %cmp, i64 %b, i64 42
+ ret i64 %Q
+}
+
+; CHECK: @test7
+; CHECK: llvm.uadd.with.overflow
+; CHECK: ret i64
+define i64 @test7(i64 %a, i64 %b) nounwind ssp {
+entry:
+ %add = add i64 %b, %a
+ %cmp = icmp ugt i64 %b, %add
+ %Q = select i1 %cmp, i64 %b, i64 42
+ ret i64 %Q
+}
+
+
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