[PATCH] D143766: [InstCombine][WIP] Fix InstCombinerImpl::foldICmpMulConstant for nsw and nuw mul with unsigned compare.

[Craig Topper via Phabricator via llvm-commits]

craig.topper created this revision.
craig.topper added reviewers: spatel, nikic, lebedev.ri.
Herald added subscribers: StephenFan, hiraditya.
Herald added a project: All.
craig.topper requested review of this revision.
Herald added a project: LLVM.

If we have both an nsw and nuw flag, we would see the nsw flag
first and only handle signed comparisons.

This patch ignores the nsw flag if the comparison isn't signed.

Will look into adding a few more tests.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D143766

Files:
  llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
  llvm/test/Transforms/InstCombine/icmp-mul.ll


Index: llvm/test/Transforms/InstCombine/icmp-mul.ll
===================================================================
--- llvm/test/Transforms/InstCombine/icmp-mul.ll
+++ llvm/test/Transforms/InstCombine/icmp-mul.ll
@@ -946,9 +946,7 @@
 
 define i1 @splat_mul_unknown_lz(i32 %x) {
 ; CHECK-LABEL: @splat_mul_unknown_lz(
-; CHECK-NEXT:    [[Z:%.*]] = zext i32 [[X:%.*]] to i128
-; CHECK-NEXT:    [[M:%.*]] = mul nuw nsw i128 [[Z]], 18446744078004518913
-; CHECK-NEXT:    [[R:%.*]] = icmp ult i128 [[M]], 39614081257132168796771975168
+; CHECK-NEXT:    [[R:%.*]] = icmp sgt i32 [[X:%.*]], -1
 ; CHECK-NEXT:    ret i1 [[R]]
 ;
   %z = zext i32 %x to i128
Index: llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
===================================================================
--- llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
+++ llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
@@ -2061,15 +2061,12 @@
     }
   }
 
-  if (!Mul->hasNoSignedWrap() && !Mul->hasNoUnsignedWrap())
-    return nullptr;
-
   // With a matching no-overflow guarantee, fold the constants:
   // (X * MulC) < C --> X < (C / MulC)
   // (X * MulC) > C --> X > (C / MulC)
   // TODO: Assert that Pred is not equal to SGE, SLE, UGE, ULE?
   Constant *NewC = nullptr;
-  if (Mul->hasNoSignedWrap()) {
+  if (Mul->hasNoSignedWrap() && ICmpInst::isSigned(Pred)) {
     // MININT / -1 --> overflow.
     if (C.isMinSignedValue() && MulC->isAllOnes())
       return nullptr;
@@ -2082,8 +2079,7 @@
     if (Pred == ICmpInst::ICMP_SLE || Pred == ICmpInst::ICMP_SGT)
       NewC = ConstantInt::get(
           MulTy, APIntOps::RoundingSDiv(C, *MulC, APInt::Rounding::DOWN));
-  } else {
-    assert(Mul->hasNoUnsignedWrap() && "Expected mul nuw");
+  } else if (Mul->hasNoUnsignedWrap()) {
     if (Pred == ICmpInst::ICMP_ULT || Pred == ICmpInst::ICMP_UGE)
       NewC = ConstantInt::get(
           MulTy, APIntOps::RoundingUDiv(C, *MulC, APInt::Rounding::UP));


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