[llvm] r204912 - InstCombine: merge constants in both operands of icmp.
Benjamin Kramer
benny.kra at gmail.com
Thu Mar 27 12:30:44 PDT 2014
On 27.03.2014, at 20:23, Erik Verbruggen <erikjv at me.com> wrote:
> Actually, I'm wondering if it's better to revert my patch (and yours). The "nightly" test-suite pointed out a regression. If you have a tight for loop, like:
> for (i = 0; i <= 39; i++)
> doSomethingHere;
>
> then before the patch it would be:
> %indvars.iv.next = add nuw nsw i64 %indvars.iv, 1
> %exitcond = icmp eq i64 %indvars.iv.next, 40
>
> while with the patch it's:
> %indvars.iv.next = add nuw nsw i64 %indvars.iv, 1
> %exitcond = icmp eq i64 %indvars.iv, 39
>
> That keeps the "old" %indvars.iv alive. This causes some performance tests to fail, like MultiSource/Benchmarks/MiBench/telecomm-gsm.
>
> I Cc-ed d0k because he did the review, so what do you guys think?
A simple fix would be to check if the add has just one use. I was hoping that this kind of workaround wouldn't be necessary anymore but it looks like we still need it in this case :|
- Ben
>
> -- Erik.
>
>
> On 27 Mar 2014, at 18:56, Reid Kleckner <rnk at google.com> wrote:
>
>> This transform was broken for unsigned comparisons. I disabled it in r204948, which should fix the problem. See the commit message for the counterexample.
>>
>>
>> On Thu, Mar 27, 2014 at 4:16 AM, Erik Verbruggen <erikjv at me.com> wrote:
>> Author: erikjv
>> Date: Thu Mar 27 06:16:05 2014
>> New Revision: 204912
>>
>> URL: http://llvm.org/viewvc/llvm-project?rev=204912&view=rev
>> Log:
>> 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.
>>
>> Modified:
>> llvm/trunk/lib/Target/README.txt
>> llvm/trunk/lib/Transforms/InstCombine/InstCombineCompares.cpp
>> llvm/trunk/test/Transforms/InstCombine/icmp.ll
>>
>> Modified: llvm/trunk/lib/Target/README.txt
>> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Target/README.txt?rev=204912&r1=204911&r2=204912&view=diff
>> ==============================================================================
>> --- llvm/trunk/lib/Target/README.txt (original)
>> +++ llvm/trunk/lib/Target/README.txt Thu Mar 27 06:16:05 2014
>> @@ -930,18 +930,6 @@ optimized with "clang -emit-llvm-bc | op
>>
>> //===---------------------------------------------------------------------===//
>>
>> -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
>>
>> Modified: llvm/trunk/lib/Transforms/InstCombine/InstCombineCompares.cpp
>> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/InstCombine/InstCombineCompares.cpp?rev=204912&r1=204911&r2=204912&view=diff
>> ==============================================================================
>> --- llvm/trunk/lib/Transforms/InstCombine/InstCombineCompares.cpp (original)
>> +++ llvm/trunk/lib/Transforms/InstCombine/InstCombineCompares.cpp Thu Mar 27 06:16:05 2014
>> @@ -3008,6 +3008,19 @@ Instruction *InstCombiner::visitICmpInst
>> // 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;
>> }
>>
>> Modified: llvm/trunk/test/Transforms/InstCombine/icmp.ll
>> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/InstCombine/icmp.ll?rev=204912&r1=204911&r2=204912&view=diff
>> ==============================================================================
>> --- llvm/trunk/test/Transforms/InstCombine/icmp.ll (original)
>> +++ llvm/trunk/test/Transforms/InstCombine/icmp.ll Thu Mar 27 06:16:05 2014
>> @@ -1356,3 +1356,56 @@ define i1 @icmp_ashr_ashr_ne(i32 %a, i32
>> %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
>> +}
>>
>>
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