[PATCH] D32954: [InstSimplify] restrict icmp fold with 2 sdiv exact operands (PR32949)

[Sanjay Patel via Phabricator via llvm-commits]

spatel created this revision.
Herald added a subscriber: mcrosier.

These folds were introduced with https://reviews.llvm.org/rL127064 as part of solving:
https://bugs.llvm.org/show_bug.cgi?id=9343

As shown here:
http://rise4fun.com/Alive/C8
...however, the sdiv exact case needs a stronger predicate.

I opted for duplicated code instead of adding another fallthrough because I think that's easier to read (and edit in case we need/want to restrict/loosen the predicates any more).

This should fix:
https://bugs.llvm.org/show_bug.cgi?id=32949
https://bugs.llvm.org/show_bug.cgi?id=32948


https://reviews.llvm.org/D32954

Files:
  lib/Analysis/InstructionSimplify.cpp
  test/Transforms/InstSimplify/compare.ll


Index: test/Transforms/InstSimplify/compare.ll
===================================================================
--- test/Transforms/InstSimplify/compare.ll
+++ test/Transforms/InstSimplify/compare.ll
@@ -598,11 +598,14 @@
   ret i1 %C
 }
 
-; FIXME: But not other preds: PR32949 - https://bugs.llvm.org/show_bug.cgi?id=32949
+; But not other preds: PR32949 - https://bugs.llvm.org/show_bug.cgi?id=32949
 
 define i1 @sdiv_exact_not_equality(i32 %Z) {
 ; CHECK-LABEL: @sdiv_exact_not_equality(
-; CHECK-NEXT:    ret i1 true
+; CHECK-NEXT:    [[A:%.*]] = sdiv exact i32 10, %Z
+; CHECK-NEXT:    [[B:%.*]] = sdiv exact i32 20, %Z
+; CHECK-NEXT:    [[C:%.*]] = icmp ult i32 [[A]], [[B]]
+; CHECK-NEXT:    ret i1 [[C]]
 ;
   %A = sdiv exact i32 10, %Z
   %B = sdiv exact i32 20, %Z
Index: lib/Analysis/InstructionSimplify.cpp
===================================================================
--- lib/Analysis/InstructionSimplify.cpp
+++ lib/Analysis/InstructionSimplify.cpp
@@ -2815,10 +2815,19 @@
       break;
     case Instruction::UDiv:
     case Instruction::LShr:
-      if (ICmpInst::isSigned(Pred))
+      if (ICmpInst::isSigned(Pred) || !LBO->isExact() || !RBO->isExact())
         break;
-      LLVM_FALLTHROUGH;
+      if (Value *V = SimplifyICmpInst(Pred, LBO->getOperand(0),
+                                      RBO->getOperand(0), Q, MaxRecurse - 1))
+          return V;
+      break;
     case Instruction::SDiv:
+      if (!ICmpInst::isEquality(Pred) || !LBO->isExact() || !RBO->isExact())
+        break;
+      if (Value *V = SimplifyICmpInst(Pred, LBO->getOperand(0),
+                                      RBO->getOperand(0), Q, MaxRecurse - 1))
+        return V;
+      break;
     case Instruction::AShr:
       if (!LBO->isExact() || !RBO->isExact())
         break;


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